Java cơ bản, b

1. Introduction to
Java Programming
Y. Daniel Liang
Edited by Hoàng Văn Hậu – VTC Academy – THSoft co.,ltd
https://play.google.com/store/apps/developer?id=THSoft+Co.,Ltd

2. Introduction
 Course Objectives
 Organization of the Book
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3. Course Objectives
 Upon completing the course, you will understand
– Create, compile, and run Java programs
– Primitive data types
– Java control flow
– Methods
– Arrays (for teaching Java in two semesters, this could be the end)
– Object-oriented programming
– Core Java classes (Swing, exception, internationalization,
multithreading, multimedia, I/O, networking, Java
Collections Framework)
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4. Course Objectives, cont.
 You will be able to
– Develop programs using Eclipse IDE
– Write simple programs using primitive data
types, control statements, methods, and arrays.
– Create and use methods
– Write interesting projects
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5. Session 03: Method and Class
 Methods
 Object-Oriented Programming
 Classes
 Packages
 Subclassingand Inheritance
 Polymorphism
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6. Introducing Methods
Method Structure
A method is a
collection of
statements that are
grouped together
to perform an
operation.
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7. Introducing Methods, cont.
•parameter profile refers to the type, order, and
number of the parameters of a method.
•method signature is the combination of the
method name and the parameter profiles.
•The parameters defined in the method header
are known as formal parameters.
•When a method is invoked, its formal
parameters are replaced by variables or data,
which are referred to as actual parameters.
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8. Declaring Methods
public static int max(int num1,
int num2) {
if (num1 > num2)
return num1;
else
return num2;
}
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9. Calling Methods, cont.
pass i
pass j
public static void main(String[] args) { public static int max(int num1, int num2) {
int i = 5; int result;
int j = 2;
int k = max(i, j); if (num1 > num2)
result = num1;
System.out.println( else
"The maximum between " + i + result = num2;
" and " + j + " is " + k);
} return result;
}
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10. Calling Methods, cont.
The main method pass 5 The max method
i: 5 num1: 5
pass 2
parameters
j: 2 num2: 2
k: 5 result: 5
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11. CAUTION
A return statement is required for a nonvoid
method. The following method is logically
correct, but it has a compilation error, because the
Java compiler thinks it possible that this method
does not return any value.
public static int xMethod(int n) {
if (n > 0) return 1;
else if (n == 0) return 0;
else if (n < 0) return –1;
}
To fix this problem, delete if (n<0) in the code.
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12. Actions on Eclipse
 Open Eclipse IDE
– Create project: Session3Ex
– Create package: com.vtcacademy.exopp
– Create java class: Ex3WithOpp.java (with main method)
– Create java class: Circle.java
Source Run
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13. The Math Class
 Class constants:
– PI
–E
 Class methods:
– Trigonometric Methods
– Exponent Methods
– Rounding Methods
– min, max, abs, and random Methods
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14. Trigonometric Methods
 sin(double a)
 cos(double a)
 tan(double a)
 acos(double a)
 asin(double a)
 atan(double a)
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15. Exponent Methods
 exp(double a)
Returns e raised to the power of a.
 log(double a)
Returns the natural logarithm of a.
 pow(double a, double b)
Returns a raised to the power of b.
 sqrt(double a)
Returns the square root of a.
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16. Rounding Methods
 double ceil(double x)
x rounded up to its nearest integer. This integer is returned as a
double value.
 double floor(double x)
x is rounded down to its nearest integer. This integer is
returned as a double value.
 double rint(double x)
x is rounded to its nearest integer. If x is equally close to two
integers, the even one is returned as a double.
 int round(float x)
Return (int)Math.floor(x+0.5).
 long round(double x)
Return (long)Math.floor(x+0.5).
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17. min, max, abs, and random
 max(a, b)and min(a, b)
Returns the maximum or minimum of two
parameters.
 abs(a)
Returns the absolute value of the parameter.
 random()
Returns a random double value
in the range [0.0, 1.0).
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18. Example 3.1 Computing Mean
and Standard Deviation
Generate n random numbers and compute the mean
and standard deviation
n n
xi n ( xi )2
i 1 xi2 i 1
mean i 1 n
n deviation
n 1
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19. Example 3.2 Obtaining Random
Characters
Write the methods for generating random
characters. The program uses these methods to
generate 175 random characters between „!' and „~'
and displays 25 characters per line. To find out the
characters between „!' and „~', see Appendix B,
“The ASCII Character Set.”
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20. OO Programming Concepts
An object A Circle object
Data Field
data field 1
radius = 5
... State
Method
data field n findArea
method 1
... Behavior
method n
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21. Class and Objects
Circle UML Graphical notation for classes
radius: double UML Graphical notation for fields
UML Graphical notation for methods
findArea(): double
new Circle() new Circle()
circle1: Circle circlen: Circle UML Graphical notation
for objects
radius = 2 ... radius = 5
Illustration on code
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22. Class Declaration
class Circle {
double radius = 1.0;
double findArea(){
return radius * radius * 3.14159;
}
}
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23. Declaring Object Reference Variables
ClassName objectReference;
Example:
Circle myCircle;
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24. Creating Objects
objectReference = new ClassName();
Example:
myCircle = new Circle();
The object reference is assigned to the object
reference variable.
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25. Declaring/Creating Objects
in a Single Step
ClassName objectReference = new ClassName();
Example:
Circle myCircle = new Circle();
Circle myCircle2;
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26. Constructors
Circle(double r) {
radius = r;
} Constructors are a
special kind of
Circle() { methods that are
radius = 1.0; invoked to construct
} objects.
myCircle = new Circle(5.0);
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27. Constructors
Circle(double r) {
radius = r;
} Constructors are a
special kind of
Circle() { methods that are
radius = 1.0; invoked to construct
} objects.
myCircle = new Circle(5.0);
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28. Constructors, cont.
A constructor with no parameters is referred to
as a default constructor.
Constructors must have the same name
as the class itself.
Constructors do not have a return type—
not even void.
Constructors are invoked using the new
operator when an object is created.
Constructors play the role of initializing
objects.
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29. Example 3.3 Using Classes from
the Java Library
 Objective: Demonstrate using classes from the
Java library. Use the JFrame class in the
javax.swing package to create two frames;
use the methods in the JFrame class to set
the title, size and location of the frames and
to display the frames.
Illustration on code
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30. Subclassing and Inheritance
 private
 None
 protected
 Public
Illustration on code
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31. Example 3.4
Shape
TwoDimensionalShape ThreeDimensionalShape
Circle Square Triangle Sphere Cube Tetrahedron
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32. Example 3.4
 http://blogs.unsw.edu.au/comp1400/blog/20
11/09/tut-10/
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33. Abstract Classes and
Methods
 Abstract classes
– Are superclasses (called abstract superclasses)
– Cannot be instantiated
– Incomplete
 subclasses fill in "missing pieces"
 Concrete classes
– Can be instantiated
– Implement every method they declare
– Provide specifics
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34. Abstract Classes and Methods
(Cont.)
 Abstract classes not required, but reduce
client code dependencies
 To make a class abstract
– Declare with keyword abstract
– Contain one or more abstract methods
public abstract void draw();
– Abstract methods
 No implementation, must be overridden
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35. Abstract Classes and Methods
(Cont.)
 Application example
– Abstract class Shape
 Declares draw as abstract method
– Circle, Triangle, Rectangle extends Shape
 Each must implement draw
– Each object can draw itself
 Iterators
– Array, ArrayList (Chapter 22)
– Walk through list elements
– Used in polymorphic programming to traverse a collection
Illustration on code
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36. Case Study: Creating and Using
Interfaces
 Use interface Shape
– Replace abstract class Shape
 Interface
– Declaration begins with interface keyword
– Classes implement an interface (and its methods)
– Contains public abstract methods
 Classes (that implement the interface) must implement these
methods
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37. 1 // Fig. 10.18: Shape.java
2 // Shape interface declaration.
3
4 public interface Shape {
5 public double getArea(); // calculate area
6 public double getVolume(); // calculate volume
7 public String getName(); // return shape name
8
9 } // end interface Shape
Lines 5-7
Classes that implement Shape
must implement these methods
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38. 1 // Fig. 10.19: Point.java
2 // Point class declaration implements interface Shape.
3
4 public class Point extends Object implements Shape {
5 private int x; // x part of coordinate pair
6 private int y; // y part of coordinate pair
7
8 // no-argument constructor; x and y default to 0
9 public Point()
10 {
11 // implicit call to Object constructor occurs here
12 }
13
14 // constructor
15 public Point( int xValue, int yValue )
16 { Error compile
17 // implicit call to Object constructor occurs here
18 x = xValue; // no need for validation
19 y = yValue; // no need for validation
20 }
21
22 // set x in coordinate pair
23 public void setX( int xValue )
24 {
25 x = xValue; // no need for validation
26 }
27
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39. Action on class
 Teacher
– hauc2@yahoo.com
– 0984380003
– https://play.google.com/store/search?q=thsoft+co&c=apps
 Captions
 Members
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