SlideShare ist ein Scribd-Unternehmen logo
1 von 52
Downloaden Sie, um offline zu lesen
Building Java Programs 
Chapter 1 
Introduction to Java Programming 
Copyright (c) Pearson 2013. 
All rights reserved.
2 
What is computer science? 
• Computer Science 
– The study of theoretical foundations of information and 
computation and their implementation and application in computer 
systems. -- Wikipedia 
– Many subfields 
• Graphics, Computer Vision 
• Artificial Intelligence 
• Scientific Computing 
• Robotics 
• Databases, Data Mining 
• Computational Linguistics, Natural Language Processing ... 
• Computer Engineering 
– Overlap with CS and EE; emphasizes hardware
3 
The CS job market 
Computer science Biological science 
160,000 
140,000 
120,000 
100,000 
80,000 
60,000 
40,000 
20,000 
- 
PhD 
Master's 
Bachelor's 
Projected Job Openings 
SOURCES: Tabulated by National Science Foundation/Division of Science Resources Statistics; data from Department of Education/National Center for Education Statistics: 
Integrated Postsecondary Education Data System Completions Survey; and NSF/SRS: Sur
4 
What is programming? 
• program: A set of instructions 
to be carried out by a computer. 
• program execution: The act of 
carrying out the instructions 
contained in a program. 
• programming language: A systematic set of rules used to 
describe computations in a format that is editable by humans. 
– This textbook teaches programming in a language named Java.
5 
Programming languages 
• Some influential ones: 
– FORTRAN 
• science / engineering 
– COBOL 
• business data 
– LISP 
• logic and AI 
– BASIC 
• a simple language
6 
Some modern languages 
• procedural languages: programs are a series of commands 
– Pascal (1970): designed for education 
– C (1972): low-level operating systems and device drivers 
• functional programming: functions map inputs to outputs 
– Lisp (1958) / Scheme (1975), ML (1973), Haskell (1990) 
• object-oriented languages: programs use interacting "objects" 
– Smalltalk (1980): first major object-oriented language 
– C++ (1985): "object-oriented" improvements to C 
• successful in industry; used to build major OSes such as Windows 
– Java (1995): designed for embedded systems, web apps/servers 
• Runs on many platforms (Windows, Mac, Linux, cell phones...) 
• The language taught in this textbook
Basic Java programs with 
println statements
8 
Compile/run a program 
1. Write it. 
– code or source code: The set of instructions in a program. 
2. Compile it. 
• compile: Translate a program from one language to another. 
– byte code: The Java compiler converts your code into a format 
named byte code that runs on many computer types. 
3. Run (execute) it. 
– output: The messages printed to the user by a program. 
source code 
compile 
byte code 
run 
output
9 
A Java program 
public class Hello { 
public static void main(String[] args) { 
System.out.println("Hello, world!"); 
System.out.println(); 
System.out.println("This program produces"); 
System.out.println("four lines of output"); 
} 
}• 
Its output: 
Hello, world! 
This program produces 
four lines of output 
• console: Text box into which 
the program's output is printed.
10 
Structure of a Java 
program 
public class name { 
class: a program 
public static void main(String[] args) { 
statement;; 
statement;; 
...... 
statement;; 
} 
} 
method: a named group 
of statements 
statement: a command to be executed 
• Every executable Java program consists of a class, 
– that contains a method named main, 
• that contains the statements (commands) to be executed.
11 
System.out.println 
• A statement that prints a line of output on the console. 
– pronounced "print-linn" 
– sometimes called a "println statement" for short 
• Two ways to use System.out.println : 
• System.out.println("text"); 
Prints the given message as output. 
• System.out.println(); 
Prints a blank line of output.
12 
Names and identifiers 
• You must give your program a name. 
public class GangstaRap { 
– Naming convention: capitalize each word (e.g. MyClassName) 
– Your program's file must match exactly (GangstaRap.java) 
• includes capitalization (Java is "case-sensitive") 
• identifier: A name given to an item in your program. 
– must start with a letter or _ or $ 
– subsequent characters can be any of those or a number 
• legal: _myName TheCure ANSWER_IS_42 $bling$ 
• illegal: me+u 49ers side-swipe Ph.D's
13 
Keywords 
• keyword: An identifier that you cannot use because it already 
has a reserved meaning in Java. 
abstract default if private this 
boolean do implements protected throw 
break double import public throws 
byte else instanceof return transient 
case extends int short try 
catch final interface static void 
char finally long strictfp volatile 
class float native super while 
const for new switch 
continue goto package synchronized
14 
Syntax 
• syntax: The set of legal structures and commands that can be 
used in a particular language. 
– Every basic Java statement ends with a semicolon ; 
– The contents of a class or method occur between { and } 
• syntax error (compiler error): A problem in the structure of 
a program that causes the compiler to fail. 
– Missing semicolon 
– Too many or too few { } braces 
– Illegal identifier for class name 
– Class and file names do not match 
...
15 
Syntax error example 
1 public class Hello { 
2 pooblic static void main(String[] args) { 
3 System.owt.println("Hello, world!")_ 
4 } 
5 } 
• Compiler output: 
Hello.java:2: <identifier> expected 
pooblic static void main(String[] args) { 
^ 
Hello.java:3: ';' expected 
} 
^ 
2 errors 
– The compiler shows the line number where it found the error. 
– The error messages can be tough to understand!
16 
Strings 
• string: A sequence of characters to be printed. 
– Starts and ends with a " quote " character. 
• The quotes do not appear in the output. 
– Examples: 
"hello" 
"This is a string. It's very long!" 
• Restrictions: 
– May not span multiple lines. 
"This is not 
a legal String." 
– May not contain a " character. 
"This is not a "legal" String either."
17 
Escape sequences 
• escape sequence: A special sequence of characters used to 
represent certain special characters in a string. 
t tab character 
n new line character 
" quotation mark character 
 backslash character 
– Example: 
System.out.println("hellonhowtare "you"?"); 
– Output: 
hello 
how are "you"?
18 
Questions 
• What is the output of the following println statements? 
System.out.println("tatbtc"); 
System.out.println(""); 
System.out.println("'"); 
System.out.println("""""); 
System.out.println("C:ninthe downward spiral"); 
• Write a println statement to produce this output: 
/  //  ///
19 
Answers 
• Output of each println statement: 
a b c 
 
' 
""" 
C: 
in he downward spiral 
• println statement to produce the line of output: 
System.out.println("/  //  /// ");
20 
Questions 
• What println statements will generate this output? 
This program prints a 
quote from the Gettysburg Address. 
"Four score and seven years ago, 
our 'fore fathers' brought forth on 
this continent a new nation." 
• What println statements will generate this output? 
A "quoted" String is 
'much' better if you learn 
the rules of "escape sequences." 
Also, "" represents an empty String. 
Don't forget: use " instead of " ! 
'' is not the same as "
21 
Answers 
• println statements to generate the output: 
System.out.println("This program prints a"); 
System.out.println("quote from the Gettysburg Address."); 
System.out.println(); 
System.out.println(""Four score and seven years ago,"); 
System.out.println("our 'fore fathers' brought forth on"); 
System.out.println("this continent a new nation.""); 
• println statements to generate the output: 
System.out.println("A "quoted" String is"); 
System.out.println("'much' better if you learn"); 
System.out.println("the rules of "escape sequences.""); 
System.out.println(); 
System.out.println("Also, "" represents an empty String."); 
System.out.println("Don't forget: use " instead of " !"); 
System.out.println("'' is not the same as "");
22 
Comments 
• comment: A note written in source code by the programmer to 
describe or clarify the code. 
– Comments are not executed when your program runs. 
• Syntax: 
// comment text, on one line 
or, 
/* comment text; may span multiple lines */ 
• Examples: 
// This is a one-line comment. 
/* This is a very long 
multi-line comment. */
23 
Using comments 
• Where to place comments: 
– at the top of each file (a "comment header") 
– at the start of every method (seen later) 
– to explain complex pieces of code 
• Comments are useful for: 
– Understanding larger, more complex programs. 
– Multiple programmers working together, who must understand 
each other's code.
24 
Comments example 
/* Suzy Student, CS 101, Fall 2019 
This program prints lyrics about ... something. */ 
public class BaWitDaBa { 
public static void main(String[] args) { 
// first verse 
System.out.println("Bawitdaba"); 
System.out.println("da bang a dang diggy diggy"); 
System.out.println(); 
// second verse 
System.out.println("diggy said the boogy"); 
System.out.println("said up jump the boogy"); 
} 
}
Static methods
26 
Algorithms 
• algorithm: A list of steps for solving a problem. 
• Example algorithm: "Bake sugar cookies" 
– Mix the dry ingredients. 
– Cream the butter and sugar. 
– Beat in the eggs. 
– Stir in the dry ingredients. 
– Set the oven temperature. 
– Set the timer. 
– Place the cookies into the oven. 
– Allow the cookies to bake. 
– Spread frosting and sprinkles onto the cookies. 
– ...
27 
Problems with algorithms 
• lack of structure: Many tiny steps; tough to remember. 
• redundancy: Consider making a double batch... 
– Mix the dry ingredients. 
– Cream the butter and sugar. 
– Beat in the eggs. 
– Stir in the dry ingredients. 
– Set the oven temperature. 
– Set the timer. 
– Place the first batch of cookies into the oven. 
– Allow the cookies to bake. 
– Set the timer. 
– Place the second batch of cookies into the oven. 
– Allow the cookies to bake. 
– Mix ingredients for frosting. 
– ...
28 
Structured algorithms 
• structured algorithm: Split into coherent tasks. 
1 Make the cookie batter. 
– Mix the dry ingredients. 
– Cream the butter and sugar. 
– Beat in the eggs. 
– Stir in the dry ingredients. 
2 Bake the cookies. 
– Set the oven temperature. 
– Set the timer. 
– Place the cookies into the oven. 
– Allow the cookies to bake. 
3 Add frosting and sprinkles. 
– Mix the ingredients for the frosting. 
– Spread frosting and sprinkles onto the cookies. 
...
29 
Removing redundancy 
• A well-structured algorithm can describe repeated tasks with 
less redundancy. 
1 Make the cookie batter. 
– Mix the dry ingredients. 
– ... 
2a Bake the cookies (first batch). 
– Set the oven temperature. 
– Set the timer. 
– ... 
2b Bake the cookies (second batch). 
3 Decorate the cookies. 
– ...
30 
A program with redundancy 
public class BakeCookies { 
public static void main(String[] args) { 
System.out.println("Mix the dry ingredients."); 
System.out.println("Cream the butter and sugar."); 
System.out.println("Beat in the eggs."); 
System.out.println("Stir in the dry ingredients."); 
System.out.println("Set the oven temperature."); 
System.out.println("Set the timer."); 
System.out.println("Place a batch of cookies into the oven."); 
System.out.println("Allow the cookies to bake."); 
System.out.println("Set the oven temperature."); 
System.out.println("Set the timer."); 
System.out.println("Place a batch of cookies into the oven."); 
System.out.println("Allow the cookies to bake."); 
System.out.println("Mix ingredients for frosting."); 
System.out.println("Spread frosting and sprinkles."); 
} 
}
31 
Static methods 
• static method: A named group of statements. 
• denotes the structure of a program 
• eliminates redundancy by code reuse 
– procedural decomposition: 
dividing a problem into methods 
• Writing a static method is like 
adding a new command to Java. 
class 
method A 
 statement 
 statement 
 statement 
method B 
 statement 
 statement 
method C 
 statement 
 statement 
 statement
32 
Using static methods 
1. Design the algorithm. 
– Look at the structure, and which commands are repeated. 
– Decide what are the important overall tasks. 
2. Declare (write down) the methods. 
– Arrange statements into groups and give each group a name. 
3. Call (run) the methods. 
– The program's main method executes the other methods to 
perform the overall task.
33 
Design of an algorithm 
// This program displays a delicious recipe for baking cookies. 
public class BakeCookies2 { 
public static void main(String[] args) { 
// Step 1: Make the cake batter. 
System.out.println("Mix the dry ingredients."); 
System.out.println("Cream the butter and sugar."); 
System.out.println("Beat in the eggs."); 
System.out.println("Stir in the dry ingredients."); 
// Step 2a: Bake cookies (first batch). 
System.out.println("Set the oven temperature."); 
System.out.println("Set the timer."); 
System.out.println("Place a batch of cookies into the oven."); 
System.out.println("Allow the cookies to bake."); 
// Step 2b: Bake cookies (second batch). 
System.out.println("Set the oven temperature."); 
System.out.println("Set the timer."); 
System.out.println("Place a batch of cookies into the oven."); 
System.out.println("Allow the cookies to bake."); 
// Step 3: Decorate the cookies. 
System.out.println("Mix ingredients for frosting."); 
System.out.println("Spread frosting and sprinkles."); 
} 
}
34 
Gives your method a name so it can be executed 
• Syntax: 
public static void name() { 
statement; 
statement; 
... 
statement; 
} 
• Example: 
public static void printWarning() { 
System.out.println("This product causes cancer"); 
System.out.println("in lab rats and humans."); 
} 
Declaring a method
35 
Calling a method 
Executes the method's code 
• Syntax: 
name(); 
– You can call the same method many times if you like. 
• Example: 
printWarning(); 
– Output: 
This product causes cancer 
in lab rats and humans.
36 
Program with static method 
public class FreshPrince { 
public static void main(String[] args) { 
rap(); // Calling (running) the rap method 
System.out.println(); 
rap(); // Calling the rap method again 
} 
// This method prints the lyrics to my favorite song. 
public static void rap() { 
System.out.println("Now this is the story all about how"); 
System.out.println("My life got flipped turned upside-down"); 
} 
} 
Output: 
Now this is the story all about how 
My life got flipped turned upside-down 
Now this is the story all about how 
My life got flipped turned upside-down
37 
Final cookie program 
// This program displays a delicious recipe for baking cookies. 
public class BakeCookies3 { 
public static void main(String[] args) { 
makeBatter(); 
bake(); // 1st batch 
bake(); // 2nd batch 
decorate(); 
} 
// Step 1: Make the cake batter. 
public static void makeBatter() { 
System.out.println("Mix the dry ingredients."); 
System.out.println("Cream the butter and sugar."); 
System.out.println("Beat in the eggs."); 
System.out.println("Stir in the dry ingredients."); 
} 
// Step 2: Bake a batch of cookies. 
public static void bake() { 
System.out.println("Set the oven temperature."); 
System.out.println("Set the timer."); 
System.out.println("Place a batch of cookies into the oven."); 
System.out.println("Allow the cookies to bake."); 
} 
// Step 3: Decorate the cookies. 
public static void decorate() { 
System.out.println("Mix ingredients for frosting."); 
System.out.println("Spread frosting and sprinkles."); 
} 
}
38 
Methods calling methods 
public class MethodsExample { 
public static void main(String[] args) { 
message1(); 
message2(); 
System.out.println("Done with main."); 
} 
public static void message1() { 
System.out.println("This is message1."); 
} 
public static void message2() { 
System.out.println("This is message2."); 
message1(); 
System.out.println("Done with message2."); 
} 
} 
• Output: 
This is message1. 
This is message2. 
This is message1. 
Done with message2. 
Done with main.
39 
Control flow 
• When a method is called, the program's execution... 
– "jumps" into that method, executing its statements, then 
– "jumps" back to the point where the method was called. 
public class MethodsExample { 
public static void main(String[] args) { 
message1(); 
message2(); 
System.out.println("Done with main."); 
} 
... 
} 
public static void message1() { 
System.out.println("This is message1."); 
} 
public static void message2() { 
System.out.println("This is message2."); 
message1(); 
System.out.println("Done with message2."); 
} 
public static void message1() { 
System.out.println("This is message1."); 
}
40 
When to use methods 
• Place statements into a static method if: 
– The statements are related structurally, and/or 
– The statements are repeated. 
• You should not create static methods for: 
– An individual println statement. 
– Only blank lines. (Put blank printlns in main.) 
– Unrelated or weakly related statements. 
(Consider splitting them into two smaller methods.)
Drawing complex figures 
with static methods
42 
Static methods question 
• Write a program to print these figures using methods. 
______ 
/  
/  
 / 
______/ 
 / 
______/ 
+--------+ 
______ 
/  
/  
| STOP | 
 / 
______/ 
______ 
/  
/  
+--------+
43 
Development strategy 
______ 
/  
/  
 / 
______/ 
 / 
______/ 
+--------+ 
______ 
/  
/  
| STOP | 
 / 
______/ 
______ 
/  
/  
+--------+ 
First version (unstructured): 
 Create an empty program and main method. 
 Copy the expected output into it, surrounding 
each line with System.out.println syntax. 
 Run it to verify the output.
44 
Program version 1 
public class Figures1 { 
public static void main(String[] args) { 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
System.out.println(" /"); 
System.out.println(" ______/"); 
System.out.println(); 
System.out.println(" /"); 
System.out.println(" ______/"); 
System.out.println("+--------+"); 
System.out.println(); 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
System.out.println("| STOP |"); 
System.out.println(" /"); 
System.out.println(" ______/"); 
System.out.println(); 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
System.out.println("+--------+"); 
} 
}
45 
Development strategy 2 
______ 
/  
/  
 / 
______/ 
 / 
______/ 
+--------+ 
______ 
/  
/  
| STOP | 
 / 
______/ 
______ 
/  
/  
+--------+ 
Second version (structured, with redundancy): 
 Identify the structure of the output. 
 Divide the main method into static methods 
based on this structure.
46 
Output structure 
______ 
/  
/  
 / 
______/ 
 / 
______/ 
+--------+ 
______ 
/  
/  
| STOP | 
 / 
______/ 
______ 
/  
/  
+--------+ 
The structure of the output: 
 initial "egg" figure 
 second "teacup" figure 
 third "stop sign" figure 
 fourth "hat" figure 
This structure can be represented by methods: 
 egg 
 teaCup 
 stopSign 
 hat
47 
Program version 2 
public class Figures2 { 
public static void main(String[] args) { 
egg(); 
teaCup(); 
stopSign(); 
hat(); 
} 
public static void egg() { 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
System.out.println(" /"); 
System.out.println(" ______/"); 
System.out.println(); 
} 
public static void teaCup() { 
System.out.println(" /"); 
System.out.println(" ______/"); 
System.out.println("+--------+"); 
System.out.println(); 
} 
...
48 
Program version 2, cont'd. 
... 
public static void stopSign() { 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
System.out.println("| STOP |"); 
System.out.println(" /"); 
System.out.println(" ______/"); 
System.out.println(); 
} 
public static void hat() { 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
System.out.println("+--------+"); 
} 
}
49 
Development strategy 3 
______ 
/  
/  
 / 
______/ 
 / 
______/ 
+--------+ 
______ 
/  
/  
| STOP | 
 / 
______/ 
______ 
/  
/  
+--------+ 
Third version (structured, without redundancy): 
 Identify redundancy in the output, and create 
methods to eliminate as much as possible. 
 Add comments to the program.
50 
Output redundancy 
The redundancy in the output: 
 egg top: reused on stop sign, hat 
 egg bottom: reused on teacup, stop sign 
 divider line: used on teacup, hat 
This redundancy can be fixed by methods: 
 eggTop 
 eggBottom 
 line 
______ 
/  
/  
 / 
______/ 
 / 
______/ 
+--------+ 
______ 
/  
/  
| STOP | 
 / 
______/ 
______ 
/  
/  
+--------+
51 
Program version 3 
// Suzy Student, CSE 138, Spring 2094 
// Prints several figures, with methods for structure and redundancy. 
public class Figures3 { 
public static void main(String[] args) { 
egg(); 
teaCup(); 
stopSign(); 
hat(); 
} 
// Draws the top half of an an egg figure. 
public static void eggTop() { 
System.out.println(" ______"); 
System.out.println(" / "); 
System.out.println("/ "); 
} 
// Draws the bottom half of an egg figure. 
public static void eggBottom() { 
System.out.println(" /"); 
System.out.println(" ______/"); 
} 
// Draws a complete egg figure. 
public static void egg() { 
eggTop(); 
eggBottom(); 
System.out.println(); 
} 
...
52 
Program version 3, cont'd. 
... 
// Draws a teacup figure. 
public static void teaCup() { 
eggBottom(); 
line(); 
System.out.println(); 
} 
// Draws a stop sign figure. 
public static void stopSign() { 
eggTop(); 
System.out.println("| STOP |"); 
eggBottom(); 
System.out.println(); 
} 
// Draws a figure that looks sort of like a hat. 
public static void hat() { 
eggTop(); 
line(); 
} 
// Draws a line of dashes. 
public static void line() { 
System.out.println("+--------+"); 
} 
}

Weitere ähnliche Inhalte

Was ist angesagt? (19)

Java tutorial PPT
Java tutorial PPTJava tutorial PPT
Java tutorial PPT
 
Java Tutorial
Java TutorialJava Tutorial
Java Tutorial
 
Java 101 intro to programming with java
Java 101  intro to programming with javaJava 101  intro to programming with java
Java 101 intro to programming with java
 
Java Basics
Java BasicsJava Basics
Java Basics
 
Java tutorials
Java tutorialsJava tutorials
Java tutorials
 
Introduction to java Programming
Introduction to java ProgrammingIntroduction to java Programming
Introduction to java Programming
 
Introduction to Java Programming
Introduction to Java ProgrammingIntroduction to Java Programming
Introduction to Java Programming
 
Java Notes
Java Notes Java Notes
Java Notes
 
Unit 8 Java
Unit 8 JavaUnit 8 Java
Unit 8 Java
 
Java history, versions, types of errors and exception, quiz
Java history, versions, types of errors and exception, quiz Java history, versions, types of errors and exception, quiz
Java history, versions, types of errors and exception, quiz
 
Learn Java Part 2
Learn Java Part 2Learn Java Part 2
Learn Java Part 2
 
Java Tutorial
Java Tutorial Java Tutorial
Java Tutorial
 
Java basic tutorial by sanjeevini india
Java basic tutorial by sanjeevini indiaJava basic tutorial by sanjeevini india
Java basic tutorial by sanjeevini india
 
Presentation to java
Presentation  to  javaPresentation  to  java
Presentation to java
 
Java Tutorial | My Heart
Java Tutorial | My HeartJava Tutorial | My Heart
Java Tutorial | My Heart
 
Java features
Java featuresJava features
Java features
 
Core Java introduction | Basics | free course
Core Java introduction | Basics | free course Core Java introduction | Basics | free course
Core Java introduction | Basics | free course
 
Java 101 Intro to Java Programming
Java 101 Intro to Java ProgrammingJava 101 Intro to Java Programming
Java 101 Intro to Java Programming
 
Java Presentation For Syntax
Java Presentation For SyntaxJava Presentation For Syntax
Java Presentation For Syntax
 

Andere mochten auch

Andere mochten auch (17)

Simple Java Programs
Simple Java ProgramsSimple Java Programs
Simple Java Programs
 
Java programming-examples
Java programming-examplesJava programming-examples
Java programming-examples
 
Java Simple Programs
Java Simple ProgramsJava Simple Programs
Java Simple Programs
 
Java codes
Java codesJava codes
Java codes
 
Introduction to java
Introduction to javaIntroduction to java
Introduction to java
 
Java Programming Basics
Java Programming BasicsJava Programming Basics
Java Programming Basics
 
Chapter 4 flow control structures and arrays
Chapter 4 flow control structures and arraysChapter 4 flow control structures and arrays
Chapter 4 flow control structures and arrays
 
Java: Collections
Java: CollectionsJava: Collections
Java: Collections
 
Preparing Java 7 Certifications
Preparing Java 7 CertificationsPreparing Java 7 Certifications
Preparing Java 7 Certifications
 
Java simple programs
Java simple programsJava simple programs
Java simple programs
 
Advance java practicalty bscit sem5
Advance java practicalty bscit sem5Advance java practicalty bscit sem5
Advance java practicalty bscit sem5
 
java collections
java collectionsjava collections
java collections
 
Java collections
Java collectionsJava collections
Java collections
 
Java Collections Tutorials
Java Collections TutorialsJava Collections Tutorials
Java Collections Tutorials
 
Introduction to Java Programming
Introduction to Java ProgrammingIntroduction to Java Programming
Introduction to Java Programming
 
Auto insurance final presentation
Auto insurance final presentationAuto insurance final presentation
Auto insurance final presentation
 
Java Certification by HUJAK - 2015-05-12 - at JavaCro'15 conference
Java Certification by HUJAK - 2015-05-12 - at JavaCro'15 conferenceJava Certification by HUJAK - 2015-05-12 - at JavaCro'15 conference
Java Certification by HUJAK - 2015-05-12 - at JavaCro'15 conference
 

Ähnlich wie Ch01 basic-java-programs

ch01-basic-java-programs.ppt
ch01-basic-java-programs.pptch01-basic-java-programs.ppt
ch01-basic-java-programs.pptMahyuddin8
 
JAVA Programming notes.ppt
JAVA Programming notes.pptJAVA Programming notes.ppt
JAVA Programming notes.pptAravindSiva19
 
Topic2IntroductionToJavaProgramming.ppt
Topic2IntroductionToJavaProgramming.pptTopic2IntroductionToJavaProgramming.ppt
Topic2IntroductionToJavaProgramming.pptralph581247
 
Fundamentals of Data Structures Unit 1.pptx
Fundamentals of Data Structures Unit 1.pptxFundamentals of Data Structures Unit 1.pptx
Fundamentals of Data Structures Unit 1.pptxVigneshkumar Ponnusamy
 
Chapter 2.4
Chapter 2.4Chapter 2.4
Chapter 2.4sotlsoc
 
Big Java Chapter 1
Big Java Chapter 1Big Java Chapter 1
Big Java Chapter 1Maria Joslin
 
Intro To C++ - Class 03 - An Introduction To C++ Programming, Part II
Intro To C++ - Class 03 - An Introduction To C++ Programming, Part IIIntro To C++ - Class 03 - An Introduction To C++ Programming, Part II
Intro To C++ - Class 03 - An Introduction To C++ Programming, Part IIBlue Elephant Consulting
 
Week1 Electronic System-level ESL Design and SystemC Begin
Week1 Electronic System-level ESL Design and SystemC BeginWeek1 Electronic System-level ESL Design and SystemC Begin
Week1 Electronic System-level ESL Design and SystemC Begin敬倫 林
 
introduction to c #
introduction to c #introduction to c #
introduction to c #Sireesh K
 
Chelberg ptcuser 2010
Chelberg ptcuser 2010Chelberg ptcuser 2010
Chelberg ptcuser 2010Clay Helberg
 
Csharp introduction
Csharp introductionCsharp introduction
Csharp introductionSireesh K
 
Introduction to C programming
Introduction to C programmingIntroduction to C programming
Introduction to C programmingRokonuzzaman Rony
 
Whole c++ lectures ITM1 Th
Whole c++ lectures ITM1 ThWhole c++ lectures ITM1 Th
Whole c++ lectures ITM1 ThAram Mohammed
 
01 introduction to cpp
01   introduction to cpp01   introduction to cpp
01 introduction to cppManzoor ALam
 
Introduction to Software Development
Introduction to Software DevelopmentIntroduction to Software Development
Introduction to Software DevelopmentZeeshan MIrza
 

Ähnlich wie Ch01 basic-java-programs (20)

ch01-basic-java-programs.ppt
ch01-basic-java-programs.pptch01-basic-java-programs.ppt
ch01-basic-java-programs.ppt
 
JAVA Programming notes.ppt
JAVA Programming notes.pptJAVA Programming notes.ppt
JAVA Programming notes.ppt
 
Java
JavaJava
Java
 
Topic2IntroductionToJavaProgramming.ppt
Topic2IntroductionToJavaProgramming.pptTopic2IntroductionToJavaProgramming.ppt
Topic2IntroductionToJavaProgramming.ppt
 
Fundamentals of Data Structures Unit 1.pptx
Fundamentals of Data Structures Unit 1.pptxFundamentals of Data Structures Unit 1.pptx
Fundamentals of Data Structures Unit 1.pptx
 
Chapter 2.4
Chapter 2.4Chapter 2.4
Chapter 2.4
 
Introduction to java programming part 1
Introduction to java programming   part 1Introduction to java programming   part 1
Introduction to java programming part 1
 
Big Java Chapter 1
Big Java Chapter 1Big Java Chapter 1
Big Java Chapter 1
 
Intro To C++ - Class 3 - Sample Program
Intro To C++ - Class 3 - Sample ProgramIntro To C++ - Class 3 - Sample Program
Intro To C++ - Class 3 - Sample Program
 
Intro To C++ - Class 03 - An Introduction To C++ Programming, Part II
Intro To C++ - Class 03 - An Introduction To C++ Programming, Part IIIntro To C++ - Class 03 - An Introduction To C++ Programming, Part II
Intro To C++ - Class 03 - An Introduction To C++ Programming, Part II
 
Week1 Electronic System-level ESL Design and SystemC Begin
Week1 Electronic System-level ESL Design and SystemC BeginWeek1 Electronic System-level ESL Design and SystemC Begin
Week1 Electronic System-level ESL Design and SystemC Begin
 
introduction to c #
introduction to c #introduction to c #
introduction to c #
 
Chelberg ptcuser 2010
Chelberg ptcuser 2010Chelberg ptcuser 2010
Chelberg ptcuser 2010
 
C intro
C introC intro
C intro
 
Csharp introduction
Csharp introductionCsharp introduction
Csharp introduction
 
Introduction to C programming
Introduction to C programmingIntroduction to C programming
Introduction to C programming
 
Whole c++ lectures ITM1 Th
Whole c++ lectures ITM1 ThWhole c++ lectures ITM1 Th
Whole c++ lectures ITM1 Th
 
01 introduction to cpp
01   introduction to cpp01   introduction to cpp
01 introduction to cpp
 
Introduction to Software Development
Introduction to Software DevelopmentIntroduction to Software Development
Introduction to Software Development
 
Intro to .NET and Core C#
Intro to .NET and Core C#Intro to .NET and Core C#
Intro to .NET and Core C#
 

Kürzlich hochgeladen

Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesMohammad Hassany
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapitolTechU
 
UKCGE Parental Leave Discussion March 2024
UKCGE Parental Leave Discussion March 2024UKCGE Parental Leave Discussion March 2024
UKCGE Parental Leave Discussion March 2024UKCGE
 
P4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdf
P4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdfP4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdf
P4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdfYu Kanazawa / Osaka University
 
Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.raviapr7
 
M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxDr. Santhosh Kumar. N
 
How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17Celine George
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICESayali Powar
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...
CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...
CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...Nguyen Thanh Tu Collection
 
CAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxCAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxSaurabhParmar42
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17Celine George
 
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxPractical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxKatherine Villaluna
 
Benefits & Challenges of Inclusive Education
Benefits & Challenges of Inclusive EducationBenefits & Challenges of Inclusive Education
Benefits & Challenges of Inclusive EducationMJDuyan
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxDr. Asif Anas
 
How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17Celine George
 
How to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 SalesHow to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 SalesCeline George
 
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfMaximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfTechSoup
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxAditiChauhan701637
 

Kürzlich hochgeladen (20)

Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming Classes
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptx
 
UKCGE Parental Leave Discussion March 2024
UKCGE Parental Leave Discussion March 2024UKCGE Parental Leave Discussion March 2024
UKCGE Parental Leave Discussion March 2024
 
P4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdf
P4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdfP4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdf
P4C x ELT = P4ELT: Its Theoretical Background (Kanazawa, 2024 March).pdf
 
Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.
 
M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptx
 
How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17
 
Prelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quizPrelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quiz
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICE
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...
CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...
CHUYÊN ĐỀ DẠY THÊM TIẾNG ANH LỚP 11 - GLOBAL SUCCESS - NĂM HỌC 2023-2024 - HK...
 
CAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxCAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptx
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17
 
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxPractical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
 
Benefits & Challenges of Inclusive Education
Benefits & Challenges of Inclusive EducationBenefits & Challenges of Inclusive Education
Benefits & Challenges of Inclusive Education
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptx
 
How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17
 
How to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 SalesHow to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 Sales
 
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfMaximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptx
 

Ch01 basic-java-programs

  • 1. Building Java Programs Chapter 1 Introduction to Java Programming Copyright (c) Pearson 2013. All rights reserved.
  • 2. 2 What is computer science? • Computer Science – The study of theoretical foundations of information and computation and their implementation and application in computer systems. -- Wikipedia – Many subfields • Graphics, Computer Vision • Artificial Intelligence • Scientific Computing • Robotics • Databases, Data Mining • Computational Linguistics, Natural Language Processing ... • Computer Engineering – Overlap with CS and EE; emphasizes hardware
  • 3. 3 The CS job market Computer science Biological science 160,000 140,000 120,000 100,000 80,000 60,000 40,000 20,000 - PhD Master's Bachelor's Projected Job Openings SOURCES: Tabulated by National Science Foundation/Division of Science Resources Statistics; data from Department of Education/National Center for Education Statistics: Integrated Postsecondary Education Data System Completions Survey; and NSF/SRS: Sur
  • 4. 4 What is programming? • program: A set of instructions to be carried out by a computer. • program execution: The act of carrying out the instructions contained in a program. • programming language: A systematic set of rules used to describe computations in a format that is editable by humans. – This textbook teaches programming in a language named Java.
  • 5. 5 Programming languages • Some influential ones: – FORTRAN • science / engineering – COBOL • business data – LISP • logic and AI – BASIC • a simple language
  • 6. 6 Some modern languages • procedural languages: programs are a series of commands – Pascal (1970): designed for education – C (1972): low-level operating systems and device drivers • functional programming: functions map inputs to outputs – Lisp (1958) / Scheme (1975), ML (1973), Haskell (1990) • object-oriented languages: programs use interacting "objects" – Smalltalk (1980): first major object-oriented language – C++ (1985): "object-oriented" improvements to C • successful in industry; used to build major OSes such as Windows – Java (1995): designed for embedded systems, web apps/servers • Runs on many platforms (Windows, Mac, Linux, cell phones...) • The language taught in this textbook
  • 7. Basic Java programs with println statements
  • 8. 8 Compile/run a program 1. Write it. – code or source code: The set of instructions in a program. 2. Compile it. • compile: Translate a program from one language to another. – byte code: The Java compiler converts your code into a format named byte code that runs on many computer types. 3. Run (execute) it. – output: The messages printed to the user by a program. source code compile byte code run output
  • 9. 9 A Java program public class Hello { public static void main(String[] args) { System.out.println("Hello, world!"); System.out.println(); System.out.println("This program produces"); System.out.println("four lines of output"); } }• Its output: Hello, world! This program produces four lines of output • console: Text box into which the program's output is printed.
  • 10. 10 Structure of a Java program public class name { class: a program public static void main(String[] args) { statement;; statement;; ...... statement;; } } method: a named group of statements statement: a command to be executed • Every executable Java program consists of a class, – that contains a method named main, • that contains the statements (commands) to be executed.
  • 11. 11 System.out.println • A statement that prints a line of output on the console. – pronounced "print-linn" – sometimes called a "println statement" for short • Two ways to use System.out.println : • System.out.println("text"); Prints the given message as output. • System.out.println(); Prints a blank line of output.
  • 12. 12 Names and identifiers • You must give your program a name. public class GangstaRap { – Naming convention: capitalize each word (e.g. MyClassName) – Your program's file must match exactly (GangstaRap.java) • includes capitalization (Java is "case-sensitive") • identifier: A name given to an item in your program. – must start with a letter or _ or $ – subsequent characters can be any of those or a number • legal: _myName TheCure ANSWER_IS_42 $bling$ • illegal: me+u 49ers side-swipe Ph.D's
  • 13. 13 Keywords • keyword: An identifier that you cannot use because it already has a reserved meaning in Java. abstract default if private this boolean do implements protected throw break double import public throws byte else instanceof return transient case extends int short try catch final interface static void char finally long strictfp volatile class float native super while const for new switch continue goto package synchronized
  • 14. 14 Syntax • syntax: The set of legal structures and commands that can be used in a particular language. – Every basic Java statement ends with a semicolon ; – The contents of a class or method occur between { and } • syntax error (compiler error): A problem in the structure of a program that causes the compiler to fail. – Missing semicolon – Too many or too few { } braces – Illegal identifier for class name – Class and file names do not match ...
  • 15. 15 Syntax error example 1 public class Hello { 2 pooblic static void main(String[] args) { 3 System.owt.println("Hello, world!")_ 4 } 5 } • Compiler output: Hello.java:2: <identifier> expected pooblic static void main(String[] args) { ^ Hello.java:3: ';' expected } ^ 2 errors – The compiler shows the line number where it found the error. – The error messages can be tough to understand!
  • 16. 16 Strings • string: A sequence of characters to be printed. – Starts and ends with a " quote " character. • The quotes do not appear in the output. – Examples: "hello" "This is a string. It's very long!" • Restrictions: – May not span multiple lines. "This is not a legal String." – May not contain a " character. "This is not a "legal" String either."
  • 17. 17 Escape sequences • escape sequence: A special sequence of characters used to represent certain special characters in a string. t tab character n new line character " quotation mark character backslash character – Example: System.out.println("hellonhowtare "you"?"); – Output: hello how are "you"?
  • 18. 18 Questions • What is the output of the following println statements? System.out.println("tatbtc"); System.out.println(""); System.out.println("'"); System.out.println("""""); System.out.println("C:ninthe downward spiral"); • Write a println statement to produce this output: / // ///
  • 19. 19 Answers • Output of each println statement: a b c ' """ C: in he downward spiral • println statement to produce the line of output: System.out.println("/ // /// ");
  • 20. 20 Questions • What println statements will generate this output? This program prints a quote from the Gettysburg Address. "Four score and seven years ago, our 'fore fathers' brought forth on this continent a new nation." • What println statements will generate this output? A "quoted" String is 'much' better if you learn the rules of "escape sequences." Also, "" represents an empty String. Don't forget: use " instead of " ! '' is not the same as "
  • 21. 21 Answers • println statements to generate the output: System.out.println("This program prints a"); System.out.println("quote from the Gettysburg Address."); System.out.println(); System.out.println(""Four score and seven years ago,"); System.out.println("our 'fore fathers' brought forth on"); System.out.println("this continent a new nation.""); • println statements to generate the output: System.out.println("A "quoted" String is"); System.out.println("'much' better if you learn"); System.out.println("the rules of "escape sequences.""); System.out.println(); System.out.println("Also, "" represents an empty String."); System.out.println("Don't forget: use " instead of " !"); System.out.println("'' is not the same as "");
  • 22. 22 Comments • comment: A note written in source code by the programmer to describe or clarify the code. – Comments are not executed when your program runs. • Syntax: // comment text, on one line or, /* comment text; may span multiple lines */ • Examples: // This is a one-line comment. /* This is a very long multi-line comment. */
  • 23. 23 Using comments • Where to place comments: – at the top of each file (a "comment header") – at the start of every method (seen later) – to explain complex pieces of code • Comments are useful for: – Understanding larger, more complex programs. – Multiple programmers working together, who must understand each other's code.
  • 24. 24 Comments example /* Suzy Student, CS 101, Fall 2019 This program prints lyrics about ... something. */ public class BaWitDaBa { public static void main(String[] args) { // first verse System.out.println("Bawitdaba"); System.out.println("da bang a dang diggy diggy"); System.out.println(); // second verse System.out.println("diggy said the boogy"); System.out.println("said up jump the boogy"); } }
  • 26. 26 Algorithms • algorithm: A list of steps for solving a problem. • Example algorithm: "Bake sugar cookies" – Mix the dry ingredients. – Cream the butter and sugar. – Beat in the eggs. – Stir in the dry ingredients. – Set the oven temperature. – Set the timer. – Place the cookies into the oven. – Allow the cookies to bake. – Spread frosting and sprinkles onto the cookies. – ...
  • 27. 27 Problems with algorithms • lack of structure: Many tiny steps; tough to remember. • redundancy: Consider making a double batch... – Mix the dry ingredients. – Cream the butter and sugar. – Beat in the eggs. – Stir in the dry ingredients. – Set the oven temperature. – Set the timer. – Place the first batch of cookies into the oven. – Allow the cookies to bake. – Set the timer. – Place the second batch of cookies into the oven. – Allow the cookies to bake. – Mix ingredients for frosting. – ...
  • 28. 28 Structured algorithms • structured algorithm: Split into coherent tasks. 1 Make the cookie batter. – Mix the dry ingredients. – Cream the butter and sugar. – Beat in the eggs. – Stir in the dry ingredients. 2 Bake the cookies. – Set the oven temperature. – Set the timer. – Place the cookies into the oven. – Allow the cookies to bake. 3 Add frosting and sprinkles. – Mix the ingredients for the frosting. – Spread frosting and sprinkles onto the cookies. ...
  • 29. 29 Removing redundancy • A well-structured algorithm can describe repeated tasks with less redundancy. 1 Make the cookie batter. – Mix the dry ingredients. – ... 2a Bake the cookies (first batch). – Set the oven temperature. – Set the timer. – ... 2b Bake the cookies (second batch). 3 Decorate the cookies. – ...
  • 30. 30 A program with redundancy public class BakeCookies { public static void main(String[] args) { System.out.println("Mix the dry ingredients."); System.out.println("Cream the butter and sugar."); System.out.println("Beat in the eggs."); System.out.println("Stir in the dry ingredients."); System.out.println("Set the oven temperature."); System.out.println("Set the timer."); System.out.println("Place a batch of cookies into the oven."); System.out.println("Allow the cookies to bake."); System.out.println("Set the oven temperature."); System.out.println("Set the timer."); System.out.println("Place a batch of cookies into the oven."); System.out.println("Allow the cookies to bake."); System.out.println("Mix ingredients for frosting."); System.out.println("Spread frosting and sprinkles."); } }
  • 31. 31 Static methods • static method: A named group of statements. • denotes the structure of a program • eliminates redundancy by code reuse – procedural decomposition: dividing a problem into methods • Writing a static method is like adding a new command to Java. class method A  statement  statement  statement method B  statement  statement method C  statement  statement  statement
  • 32. 32 Using static methods 1. Design the algorithm. – Look at the structure, and which commands are repeated. – Decide what are the important overall tasks. 2. Declare (write down) the methods. – Arrange statements into groups and give each group a name. 3. Call (run) the methods. – The program's main method executes the other methods to perform the overall task.
  • 33. 33 Design of an algorithm // This program displays a delicious recipe for baking cookies. public class BakeCookies2 { public static void main(String[] args) { // Step 1: Make the cake batter. System.out.println("Mix the dry ingredients."); System.out.println("Cream the butter and sugar."); System.out.println("Beat in the eggs."); System.out.println("Stir in the dry ingredients."); // Step 2a: Bake cookies (first batch). System.out.println("Set the oven temperature."); System.out.println("Set the timer."); System.out.println("Place a batch of cookies into the oven."); System.out.println("Allow the cookies to bake."); // Step 2b: Bake cookies (second batch). System.out.println("Set the oven temperature."); System.out.println("Set the timer."); System.out.println("Place a batch of cookies into the oven."); System.out.println("Allow the cookies to bake."); // Step 3: Decorate the cookies. System.out.println("Mix ingredients for frosting."); System.out.println("Spread frosting and sprinkles."); } }
  • 34. 34 Gives your method a name so it can be executed • Syntax: public static void name() { statement; statement; ... statement; } • Example: public static void printWarning() { System.out.println("This product causes cancer"); System.out.println("in lab rats and humans."); } Declaring a method
  • 35. 35 Calling a method Executes the method's code • Syntax: name(); – You can call the same method many times if you like. • Example: printWarning(); – Output: This product causes cancer in lab rats and humans.
  • 36. 36 Program with static method public class FreshPrince { public static void main(String[] args) { rap(); // Calling (running) the rap method System.out.println(); rap(); // Calling the rap method again } // This method prints the lyrics to my favorite song. public static void rap() { System.out.println("Now this is the story all about how"); System.out.println("My life got flipped turned upside-down"); } } Output: Now this is the story all about how My life got flipped turned upside-down Now this is the story all about how My life got flipped turned upside-down
  • 37. 37 Final cookie program // This program displays a delicious recipe for baking cookies. public class BakeCookies3 { public static void main(String[] args) { makeBatter(); bake(); // 1st batch bake(); // 2nd batch decorate(); } // Step 1: Make the cake batter. public static void makeBatter() { System.out.println("Mix the dry ingredients."); System.out.println("Cream the butter and sugar."); System.out.println("Beat in the eggs."); System.out.println("Stir in the dry ingredients."); } // Step 2: Bake a batch of cookies. public static void bake() { System.out.println("Set the oven temperature."); System.out.println("Set the timer."); System.out.println("Place a batch of cookies into the oven."); System.out.println("Allow the cookies to bake."); } // Step 3: Decorate the cookies. public static void decorate() { System.out.println("Mix ingredients for frosting."); System.out.println("Spread frosting and sprinkles."); } }
  • 38. 38 Methods calling methods public class MethodsExample { public static void main(String[] args) { message1(); message2(); System.out.println("Done with main."); } public static void message1() { System.out.println("This is message1."); } public static void message2() { System.out.println("This is message2."); message1(); System.out.println("Done with message2."); } } • Output: This is message1. This is message2. This is message1. Done with message2. Done with main.
  • 39. 39 Control flow • When a method is called, the program's execution... – "jumps" into that method, executing its statements, then – "jumps" back to the point where the method was called. public class MethodsExample { public static void main(String[] args) { message1(); message2(); System.out.println("Done with main."); } ... } public static void message1() { System.out.println("This is message1."); } public static void message2() { System.out.println("This is message2."); message1(); System.out.println("Done with message2."); } public static void message1() { System.out.println("This is message1."); }
  • 40. 40 When to use methods • Place statements into a static method if: – The statements are related structurally, and/or – The statements are repeated. • You should not create static methods for: – An individual println statement. – Only blank lines. (Put blank printlns in main.) – Unrelated or weakly related statements. (Consider splitting them into two smaller methods.)
  • 41. Drawing complex figures with static methods
  • 42. 42 Static methods question • Write a program to print these figures using methods. ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+
  • 43. 43 Development strategy ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+ First version (unstructured):  Create an empty program and main method.  Copy the expected output into it, surrounding each line with System.out.println syntax.  Run it to verify the output.
  • 44. 44 Program version 1 public class Figures1 { public static void main(String[] args) { System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); System.out.println(" /"); System.out.println(" ______/"); System.out.println(); System.out.println(" /"); System.out.println(" ______/"); System.out.println("+--------+"); System.out.println(); System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); System.out.println("| STOP |"); System.out.println(" /"); System.out.println(" ______/"); System.out.println(); System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); System.out.println("+--------+"); } }
  • 45. 45 Development strategy 2 ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+ Second version (structured, with redundancy):  Identify the structure of the output.  Divide the main method into static methods based on this structure.
  • 46. 46 Output structure ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+ The structure of the output:  initial "egg" figure  second "teacup" figure  third "stop sign" figure  fourth "hat" figure This structure can be represented by methods:  egg  teaCup  stopSign  hat
  • 47. 47 Program version 2 public class Figures2 { public static void main(String[] args) { egg(); teaCup(); stopSign(); hat(); } public static void egg() { System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); System.out.println(" /"); System.out.println(" ______/"); System.out.println(); } public static void teaCup() { System.out.println(" /"); System.out.println(" ______/"); System.out.println("+--------+"); System.out.println(); } ...
  • 48. 48 Program version 2, cont'd. ... public static void stopSign() { System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); System.out.println("| STOP |"); System.out.println(" /"); System.out.println(" ______/"); System.out.println(); } public static void hat() { System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); System.out.println("+--------+"); } }
  • 49. 49 Development strategy 3 ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+ Third version (structured, without redundancy):  Identify redundancy in the output, and create methods to eliminate as much as possible.  Add comments to the program.
  • 50. 50 Output redundancy The redundancy in the output:  egg top: reused on stop sign, hat  egg bottom: reused on teacup, stop sign  divider line: used on teacup, hat This redundancy can be fixed by methods:  eggTop  eggBottom  line ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+
  • 51. 51 Program version 3 // Suzy Student, CSE 138, Spring 2094 // Prints several figures, with methods for structure and redundancy. public class Figures3 { public static void main(String[] args) { egg(); teaCup(); stopSign(); hat(); } // Draws the top half of an an egg figure. public static void eggTop() { System.out.println(" ______"); System.out.println(" / "); System.out.println("/ "); } // Draws the bottom half of an egg figure. public static void eggBottom() { System.out.println(" /"); System.out.println(" ______/"); } // Draws a complete egg figure. public static void egg() { eggTop(); eggBottom(); System.out.println(); } ...
  • 52. 52 Program version 3, cont'd. ... // Draws a teacup figure. public static void teaCup() { eggBottom(); line(); System.out.println(); } // Draws a stop sign figure. public static void stopSign() { eggTop(); System.out.println("| STOP |"); eggBottom(); System.out.println(); } // Draws a figure that looks sort of like a hat. public static void hat() { eggTop(); line(); } // Draws a line of dashes. public static void line() { System.out.println("+--------+"); } }