Java basic

Object Oriented
Programming in JAVA

Introduction
Java is a powerful, cross-platform, object-
oriented programming language originally
developed by James Gosling at Sun Microsystems
and released in 1995 as a core component of Sun
Microsystems' Java platform. Java was originally
called OAK, and was designed for advanced
software for consumer electronics.
Java is an object-oriented language similar to C++.
The language derives much of its syntax from C
and C++ programming language.
2/3/2015 Object Oriented Programming using JAVA 2

Features of Java
• Simple
• Object-oriented
• Network-savvy
• Robust
• Interpreted
• Secure
• Architecture neutral
• Portable
• High-performance
• Multithreaded

Why Java is Important
• Two reasons :
– Trouble with C/C++ language is that they are not
portable and are not platform independent
languages.
– Emergence of World Wide Web, which demanded
portable programs
• Portability and security necessitated the
invention of Java

History
• James Gosling - Sun Microsystems
• Co founder – Vinod Khosla
• Oak - Java, May 20, 1995, Sun World
• JDK Evolutions
– JDK 1.0 (January 23, 1996)
– JDK 1.1 (February 19, 1997)
– J2SE 1.2 (December 8, 1998)
– J2SE 1.3 (May 8, 2000)
– J2SE 1.4 (February 6, 2002)
– J2SE 5.0 (September 30, 2004)
– Java SE 6 (December 11, 2006)
– Java SE 7 (July 28, 2011)

Cont..
• Java Editions.
J2SE(Java 2 Standard Edition) - to develop
client-side standalone applications or applets.
J2ME(Java 2 Micro Edition ) - to develop
applications for mobile devices such as cell
phones.
J2EE(Java 2 Enterprise Edition ) - to develop
server-side applications such as Java servlets
and Java ServerPages.

What is java?
• A general-purpose object-oriented language.
• Write Once Run Anywhere (WORA).
• Designed for easy Web/Internet applications.
• Widespread acceptance.

How is Java different from C…
• C Language:
– Major difference is that C is a structure oriented language and
Java is an object oriented language and has mechanism to
define classes and objects.
– Java does not support an explicit pointer type
– Java does not have preprocessor, so we cant use #define,
#include and #ifdef statements.
– Java does not include structures, unions and enum data types.
– Java does not include keywords like goto, sizeof and typedef.
– Java adds labeled break and continue statements.
– Java adds many features required for object oriented
programming.

How is Java different from C++…
• C++ language
Features removed in java:
Java doesn’t support pointers to avoid unauthorized access
of memory locations.
Java does not include structures, unions and enum data
types.
Java does not support operator over loading.
Preprocessor plays less important role in C++ and so
eliminated entirely in java.
Java does not perform automatic type conversions that
result in loss of precision.

Cont…
 Java does not support global variables. Every method
and variable is declared within a class and forms part of
that class.
 Java does not allow default arguments.
 Java does not support inheritance of multiple super
classes by a sub class (i.e., multiple inheritance). This is
accomplished by using ‘interface’ concept.
 It is not possible to declare unsigned integers in java.
 In java objects are passed by reference only. In C++
objects may be passed by value or reference.

Cont …
New features added in Java:
 Multithreading, that allows two or more pieces of the
same program to execute concurrently.
 C++ has a set of library functions that use a common
header file. But java replaces it with its own set of API
classes.
 It adds packages and interfaces.
 Java supports automatic garbage collection.
 break and continue statements have been enhanced in
java to accept labels as targets.
 The use of unicode characters ensures portability.

Cont …
Features that differ:
 Though C++ and java supports Boolean data type, C++ takes
any nonzero value as true and zero as false. True and false in
java are predefined literals that are values for a boolean
expression.
 Java has replaced the destructor function with a finalize()
function.
 C++ supports exception handling that is similar to java's.
However, in C++ there is no requirement that a thrown
exception be caught.

Characteristics of Java
• Java is simple
• Java is object-oriented
• Java is distributed
• Java is interpreted
• Java is robust
• Java is architecture-neutral
• Java is portable
• Java’s performance
• Java is multithreaded
• Java is dynamic
• Java is secure

Java Environment
• Java includes many development tools, classes and
methods
– Development tools are part of Java Development Kit (JDK) and
– The classes and methods are part of Java Standard Library (JSL),
also known as Application Programming Interface (API).
• JDK constitutes of tools like java compiler, java
interpreter and many.
• API includes hundreds of classes and methods grouped
into several packages according to their functionality.

Java is architecture-neutral
JAVA Program Execution

WORA(Write Once Run Anywhere)

Java Variable
–In Java Objects store there states in
variables. Variable are used as
container to hold some kind of
value(int, long, string…) during life of
application.

Java Types of Variable
• Variable in Java can be defined in different parts
of code(Inside class, Inside method, As Method
Argument) and can have different modifiers.
Depending on these conditions variables can be
divided as 4 types.
• Instance Variable
• Static Variable
• Local Variable
• Method Parameter

Instance Variable
Instance variables are used by Objects to store
there states. Variables which are defined
without STATIC keyword and Outside any
method declaration are object specific and
known as Instance variable. Variables are
known as instance variables because there
values are instance specific and values of
these variables are not shared among
instances.

Java Data types
Data types: It define the natures of value in
programing, Based on the data type of a variable,
the operating system allocates memory and
decides what can be stored in the reserved
memory. Therefore, by assigning different data
types to variables, you can store integers,
decimals, or characters in these variables.
There are two data types available in Java:
• Primitive Data Types
• Reference/Object Data Types

Java Data types
Primitive Data Types
• There are eight primitive data types supported by Java. Primitive data
types are predefined by the language and named by a keyword. Let us
now look into detail about the eight primitive data types.
1. Char
2. Boolean
3. Byte
4. Short
5. Int
6. Long
7. Doubble
8. Float

Java Data types
Primitive Data Types
• There are eight primitive data types supported by Java. Primitive data types are
predefined by the language and named by a keyword. Let us now look into detail
about the eight primitive data types.
1. Char
2. Boolean
3. Byte
4. Short
5. Int
6. Long
7. Doubble
8. Float
Reference Data Types:
• Reference variables are created using defined constructors of the classes. They are
used to access objects. These variables are declared to be of a specific type that
cannot be changed. For example, Employee, Puppy etc.

Java Operator
Operators are used to perform specific kind of operation like they do in
other programming language.
Types of Operator:
• Arithmetic Operators
• Relational Operators
• Post increment/Pre increment
• Post decrement/pre decrement
• Logical Operators
• Assignment Operators
• Misc Operators

The if statement
The if-else statement
The if-else-if statement
The ? : Conditional operator
Decision Control in Java
The switch-case statements

Java : if statement
if(this condition is true)
Execute this statement;
import java.util.Scanner;
public class Test
{
public static void main(String[] args)
{
Scanner s = new Scanner(System.in);
System.out.print("Enter age number: ");
int age = s.nextInt();
if(age>18)
{
System.out.println(“You are able for vote….”);
}
}

else
Execute this
public class Test
{
{
if(age>18)
{
}
else
{
System.out.println(“You are not able for vote….”);
}
}

else
Execute this
public class Test
{
{
if(age>18)
{
}
else
{
System.out.println(“You are not able for vote….”);
}
}
Scanner reader = new Scanner(System.in); char c = reader.nextChar();
System.out.println("nEnter the first character: ");
ch1 = (char)s.nextInt();

Loops in C
A loop is a part of the program through which the control
moves several times during the execution of program.
The part which is executed again and again is known as
the body of the loop.
In C we have three types of loops.
The for loop
The while loop
The do while loop

ForLoops
The C for statement has the following form:
for (initializes; terminate test;modifier)

While loop
The general format of the while loop is
while (expression)
{
statement a;
statement b;
}
Note:- There will be no semicolon at the end of the line containing the
keyword while.

D0..While loop
The general format of the do while loop is
do
{
statement a;
statement b:
}
while(expression);

Foreach loop
Syntax:
Syntax : for(data-type variable_name:array-name)
public class Foreach {
public static void main(String args[])
{
int[] a={10,20,30,40,50};
for(int x:a)
{
System.out.println(x);
}
}
}

The Java Jump Statement
Jump statements are used to transfer control to other parts of the program.
There are three types of Jump statement in java:
1. Break
2. Continue
3. Return
The break statement can be used in 3 ways in java.
a. Firstly, as we have seen in the switch statement, it ends the statement
sequence.
b. Secondly, it can be used as a form of goto statement to pass control to some
specific location in your program.
c. Thirdly, it is also used to exit from some loop. it is used inside the loop along
with some conditional statement and if that conditional statement
evaluates to true, then the break gets executed and the loop gets
terminated immediately.

Break Example
class BreakLoop
{
public static void main (String args[])
{
for(int x=0;x<50;x++)
{
if (x==5)
{
break;
System.out.println(“Value of x is : ” +x);
}
}
System.out.println(“Breaked out of loop”);
}
}

Continue
class BreakLoop
{
public static void main (String args[])
{
for(int x=0;x<50;x++)
{
if (x==5)
{
continue;
System.out.println(“Value of x is : ” +x);
}
}
System.out.println(“Breaked out of loop”);
}
}

Label with goto :
Label break statement is used to transfer control unconditionally from
one place to another place in program.
class labetest1{
public static void main(String arng[]){
int num;
go:{
Scanner data = new Scanner(System.in);
System.out.println("Enter a number");
num=data.nextInt();
if(num>20)
{
System.out.println("You are not a");
break go;
}
}
System.out.println("smart person"); } }

Return :
The return statement is the last jump statement. The return statement is used to
end the execution of a specific method and then return a value.
This is used in class concept with method
in next syllabus.

Array:
Array is a data structure in java that can hold one or more values in a single variable.
Array is a collection of similar type of values.
Java has two types of arrays, single dimensional and multidimensional arrays.
A few main points about arrays in Java:
Single Dimensional Array
Multi Dimensional Array
To declare a one-dimensional array, you will
use this general form:
type[ ] array-name = new type[size];

Array:Assigning Values to an Array
You can assign values to individual array elements, by using the index number, like:
double[] balance = new double[10];
balance[0] = 4500.0;
You can assign values to the array at the time of declaration, like:
double[] balance = { 2340.0, 4523.69, 3421.0};
You can also create and initialize an array, like:
int [] marks = new int[5] { 99, 98, 92, 97, 95};
In the preceding case, you may also omit the size of the array, like:
int [] marks = new int[] { 99, 98, 92, 97, 95};
int[] score = marks;

Array:Example of Single Dim Array
class MainClass
{
{
int[] arr ={ 10, 20, 30, 40, 50 };
for(i=0;i<arr.length;i++)
{
SOP("Value is: " + arr[i]);
}
}
}

Array:Input Array element and sum
class group{
public static void main(String arng[]){
int total = 0;
int sum[]=new int[5];
Scanner data = new Scanner(System.in);
System.out.println("Enter 5 element of array");
for(int i=0; i<5;i++)
sum[i] = data.nextInt();
for(int i=0; i < 5;i++)
total = total +sum[i];
System.out.println("Sum of array element is:"+total);
}
}

Soring in java
 Definition: Sorting means to put data in order;
either numerically or alphabetically.
Ways to sort arrays:
1. Array with Method
2. Bubble Sort

Soring in java
 Bubble Sort Method
In the bubble sort, as elements are sorted they gradually "bubble"
(or rise) to their proper location in the array, like bubbles rising in a
glass of soda. The bubble sort repeatedly compares adjacent
elements of an array. The first and second elements are compared
and swapped if out of order. Then the second and third elements
are compared and swapped if out of order. This sorting process
continues until the last two elements of the array are compared and
swapped if out of order

Array:Sort the Array elements with Method
import java.util.Arrays;
class Sort
{
{
int data[] = { 4, -5, 2, 6, 1 };
Arrays.sort(data);
for (int c: data)
{
System.out.println(c);
}
}
}

Array:Sort the Array elements using bubble sort
class BubbleSort {
public static void main(String []args) {
int n, c, d, swap;
Scanner in = new Scanner(System.in);
System.out.println("Input number of integers to sort");
n = in.nextInt();
int array[] = new int[n];
System.out.println("Enter " + n + " integers");
for (c = 0; c < n; c++)
array[c] = in.nextInt();

Array: bubble sort Continue…….
for (c = 0; c < ( n - 1 ); c++) {
for (d = 0; d < n - c - 1; d++) {
if (array[d] < array[d+1]) /* For ascscending order use < */
{
swap = array[d];
array[d] = array[d+1];
array[d+1] = swap;
}
}
}
System.out.println("Sorted list of numbers");
for (c = 0; c < n; c++)
System.out.println(array[c]);
}
}

Array: 2D Array
Two-dimensional arrays are defined as "an array of arrays". Since an array type is a first-class Java
type, we can have an array of ints, an array of Strings, or an array of Objects.
Syntax:
int[][] a2 = new int[10][5]
E.G
public class two
{
public static void main(String[] args) {
int[][] a2 = new int[10][5];
for (int i=0; i<a2.length; i++) {
for (int j=0; j<a2[i].length; j++) {
a2[i][j] = i;
System.out.print(" " + a2[i][j]);
}
System.out.println("");
} } }

Array: 2D Array Sum of Matrix
class Array1
{
{
int m, n, c, d;
System.out.println("Enter the number of rows and columns of matrix");
m = in.nextInt();
n = in.nextInt();
int first[][] = new int[m][n];
int second[][] = new int[m][n];
int sum[][] = new int[m][n];

Array: 2D Array Continue…..
System.out.println("Enter the elements of first matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
first[c][d] = in.nextInt();
System.out.println("Enter the elements of second matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
second[c][d] = in.nextInt();
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
sum[c][d] = first[c][d] + second[c][d];
System.out.println("Sum of entered matrices:-");
for ( c = 0 ; c < m ; c++ )
{
for ( d = 0 ; d < n ; d++ )
System.out.print(sum[c][d]+"t");
System.out.println();
}
} }

Array: 2D Array with transpose
class TransposeAMatrix
{
{
int m, n, c, d;
System.out.println("Enter the number of rows and columns of
matrix");
m = in.nextInt();
n = in.nextInt();
int matrix[][] = new int[m][n];
System.out.println("Enter the elements of matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
matrix[c][d] = in.nextInt();

Array: 2D Array with transpose Continue….
int transpose[][] = new int[n][m];
for ( c = 0 ; c < m ; c++ )
{
for ( d = 0 ; d < n ; d++ )
transpose[d][c] = matrix[c][d];
}
System.out.println("Transpose of entered matrix:-");
for ( c = 0 ; c < n ; c++ )
{
for ( d = 0 ; d < m ; d++ )
System.out.print(transpose[c][d]+"t");
System.out.print("n");
}
}
}

Array: Array with String
Java Strings are combination of characters that are widely used in java
programming.
char[] array = { 'z', 'a', 'b' };
String [] name={“amit”,”ravi”,”shyam”}
class Str
{
static String[] firstnames={ “Mohit", “Rohit", “Gopal", "Mary","Anne"
};
{
for(int i=0;i<5;i++){
System.out.println(firstnames[i]);
}
}
}

Array: Find the length of string
programming.
char[] array = { 'z', 'a', 'b' };
String [] name={“amit”,”ravi”,”shyam”}
public class stringtest
{
String Strex = "Strings are supported in java by using String class";
String strex1 = new String();
strex1 = "Java comes up with string class";
System.out.println("String length=" + Strex.length());
System.out.println("String length=" + strex1.length());
}

Array: java string replace method
programming.
public class two {
String Strex = "Strings are supported in java by using String java class"; // creating simple
Strex = "Java comes up with string class";
System.out.println("The actual string: " + Strex);
System.out.println("String after replace: " + Strex.replace('c', 'C'));
}
}

Array: java string split method
java split string method of String class and breaks string completely by a given
regular expression.
public class splittest {
String Strex;
Strex ="name is: Gopal and age is: 30 and salary is: Rs.5000";
for (String Strsplit: Strex.split(" and "))
{
System.out.println(Strsplit);
}
}
}

The Java Oops
Object Oriented Programming (OOP) is a programming concept used in several modern programming
languages, like C++, Java and Python. Before Object Oriented Programming programs were viewed as
procedures that accepted data and produced an output.
What is Class: Java is a purly an Object Oriented Language. Everything in java is an
object. These objects are created from classes which are either user-defined or built n.
Classes are also called as Templates because they provide the basic framework of an
object. A Class does not hold any value unless and until it is used for object creation.

The Java Class Example
class A
{
private static int addIntegers(int a, int b)
{
return (a+b);
}
}
{
int val1 = 10;
int val2 = 20;
System.out.println("Answer = " + addIntegers(val1, val2));
}
}

The Java Class with method and parameter
class rectangle
{
double l,w;
void get()
{
l=5;
w=5;
}
void area()
{
double a;
a=l*w;
System.out.println("Area is:"+a);
}
class Callmethod
{
{
rectangle r=new rectangle();
r.get();
r.area();
}
}

The Java Class with method and parameter
class Rectangle
{
int length,width;
void getData(int x, int y)//method
{
length=x;
width=y;
}
int rectArea()
{
int area=length*width;
return(area);
}
}
class GradeBook
{
{
Rectangle rect1= new Rectangle();
//one way of passing values to object
rect1.length=15;
rect1.width=10;
int area1=rect1.length*rect1.width;
System.out.println("Area1="+area1);
} }

The Java Constructor
Constructor:- A Constructor is a special method that does not
have a return type and a has the same name as that of the
class name. It means that a constructor can act as a normal
method or function but it cannot return any value.
Every class must have at least one constructor.
If there are no constructors for your class, the compiler will
supply a default constructor (no-arg constructor).
A constructor is used to construct an object.
A constructor looks like a method and is sometimes called a
constructor method.
A constructor never returns a value

The Java Default Constructor Example
class box
{
int l,w;
box()
{
l=5;
w=5;
}
void show()
{
System.out.println("Length is:"+l);
System.out.println("width is:"+w);
} }
class GradeBook
{
{
box b=new box();
b.show(); } }

The Java Constructor Example
class Rectangle
{
int length, width;
Rectangle(int x, int y)//define constru
{
length=x;
width=y;
}
int rectArea()//method
{
return(length*width); } }
class GradeBook
{
{
Rectangle rect1= new Rectangle(10,20);//calling constr.
int area1=rect1.rectArea();
System.out.println("Area1="+area1);
} }

• Constructor can take value, value is called
“Argument”.
• Argument can be of many types i.e integer,
character, array or any object.
• Constructor can take any no of arguments.
Java Parameterized constructor

class Rectangle {
int length; int breadth;
Rectangle(int len,int bre) {
length = len; breadth = bre;
} }
class RectangleDemo {
public static void main(String args[]) {
Rectangle r1 = new Rectangle(20,10);
System.out.println("Length of Rectangle : " + r1.length);
System.out.println("Breadth of Rectangle : " + r1.breadth);
} }
Parameterized constructor: example

Constructor chaining occurs when a class inherits
another class i.e. in inheritance, as in inheritance
sub class inherits the properties of super class.
Both the super and sub class may have
constructor methods, when an object of sub class
is created it's constructor is invoked it initializes
sub class attributes, now super class constructor
needs to be invoked, to achieve this java provides
a super keyword through which we can pass
arguments to super class constructor.
Java Constructor Chaining

• class Vehicle{
• int speed=50;
• }
•
• class Bike extends Vehicle{
• int speed=100;
•
• void display(){
• System.out.println(super.speed);//will print speed of Vehicle now
• }
• public static void main(String args[]){
• Bike b=new Bike();
• b.display();
•
• }
• }
Java Constructor Chaining Example

• this keyword is used to refer current object
in java programming.
• We can use this keyword in any method or
constructor.
• Use this method referes to the current object
that calls a method or invokes constructor.
Use of this

class Rectangle {
int length; int breadth;
void setDiamentions(int ln,int br) {
this.length = ln;
this.breadth = br;
} }
Rectangle r1 = new Rectangle(); r1.setDiamentions(20,10);
System.out.println("Length of Rectangle : " + r1.length);
System.out.println("Breadth of Rectangle : " + r1.breadth);
} }
Example

• Object is created using new operator.
• Object gets memory inside the “heap”.
• In C++ , After using object, Memory for objects
gets deallocated by delete().
• In Java deallocation can be done automatically.
• Automatic technique used to deallocate memory
is called “Garbage Collections”.
• Java is smart enough to identify the unused
object or unless objects.
Garbage Collections:Destroying Objects in Java

• Garbage collection is done automatically in java
• As soon as compiler detects that-object is no
longer needed inside the program, Garbage
collection algorithm gets executed automatically
to free up memory from the heap so that free
memory can be used by another objects.
• Different Java Runtimes may have different
approaches for garbage collection.
How garbage collection works?

• In java we can define many number of
methods in a class with same name.
• Defining two or more method with same
name is known as “Method overloading”.
• Compiler determines which method has to
execute automatically.
Method Overloading

class Rectangle {
double length; double breadth;
void area(int length, int width) {
int areaOfRectangle = length * width;
System.out.println("Area of Rectangle : " + areaOfRectangle); }
void area(double length, double width) {
double areaOfRectangle = length * width;
System.out.println("Area of Rectangle : " + areaOfRectangle); } }
Rectangle r1 = new Rectangle();
r1.area(10, 20); r1.area(10.50, 20.50);
} }
Method Overloading Example

Class Rectangle{
Int length;
Int width;
Rectangle(int l, int w){
Length=l;
Width=w; }
Void area(Rectangle r1){
Areaofrec= r1.length*r1.breadth;
S.o.p(“area is:” +areaofrec);
}}
Class RectangleDemo{
Psvm{
Rectangle r1=new Rectangle(10,20);
R1.area(r1);
}}
Java Passing an object as parameter

• Packages are used in Java in order to prevent naming conflicts, to
control access, to
• make searching/locating and usage of classes, interfaces,
enumerations and
• annotations easier, etc.
• A Package can be defined as a grouping of related types(classes,
interfaces,
• enumerations and annotations ) providing access protection and
name space
• management.
• Some of the existing packages in Java are::
• java.lang - bundles the fundamental classes
• java.io - classes for input , output functions are bundled in this
package
Packages in Java

• When creating a package, you should choose a name
for the package and put a
• package statement with that name at the top of every
source file that contains the
• classes, interfaces, enumerations, and annotation
types that you want to include in the
• package.
• The package statement should be the first line in the
source file. There can be only one
• package statement in each source file, and it applies to
all types in the file.
How to create Package in Java

• package MyPack;
• class Balance {
• String name;
• double bal;
• Balance(String n, double b) {
• name = n;
• bal = b;
• }
• void show() {
• if(bal<0)
• System.out.print("--> ");
• System.out.println(name + ": $" + bal);
• }
• }
Package Example

• class AccountBalance {
• public static void main(String args[]) {
• Balance current[] = new Balance[3];
• System.out.println(name + ": $" + bal);
• }
• }
• class AccountBalance {
• Balance current[] = new Balance[3];
• current[0] = new Balance("K. J. Fielding", 123.23);
• current[1] = new Balance("Will Tell", 157.02);
• current[2] = new Balance("Tom Jackson", -12.33);
• for(int i=0; i<3; i++) current[i].show();
• }
• }
Package Example Continue

The import Keyword:
• If a class wants to use another class in the same package, the package name does not
• need to be used. Classes in the same package find each other without any special
• syntax.
• Example:
• Here, a class named Boss is added to the payroll package that already contains
• Employee. The Boss can then refer to the Employee class without using the payroll
• prefix, as demonstrated by the following Boss class.
• package payroll;
• public class Boss
• {
• public void payEmployee(Employee e)
• {
• e.mailCheck();
• }
• }
How Packages are import in Java

Continue..
• What happens if Boss is not in the payroll package? The Boss class must
then use one
• of the following techniques for referring to a class in a different package.
• The fully qualified name of the class can be used. For example:
• payroll.Employee
• The package can be imported using the import keyword and the wild card
(*).
• For example:
• import payroll.*;
• The class itself can be imported using the import keyword. For example:
• import payroll.Employee;
• Note: A class file can contain any number of import statements. The
import
• statements must appear after the package statement and before the class
declaration.

class A
{
int i;int j;
void showij(){
System.out.println("i and j:" +i+" "+j);
} }
class B extends A {
int k;
void showk() {
System.out.println("K:" +k);
}
void sum() {
System.out.println("i+j+k:" +(i+j+k));
}
}
Inheritance in Java

class SimpleInheritance {
public static void main(String arg[]){
A superOb=new A();
B subOb=new B();
superOb.i=10; superOb.j=20;
System.out.println("Contents of SuperOb:");
superOb.showij();
subOb.i=7; subOb.j=8; subOb.k=9;
System.out.println("contents of subob:");
subOb.showij();
subOb.showk();
System.out.println("Sum of i,j and k in subOb:");
subOb.sum();
}
}2/3/2015 Object Oriented Programming using JAVA 82
Inheritance in Java…

• class A {
• int i;
• private int j;
• void setij(int x, int y) {
• i = x; j = y; } }
• class B extends A {
• int total;
• void sum() {
• total = i + j; } }
• class Access {
• B subOb = new B();
• subOb.setij(10, 12);
• subOb.sum();s
• System.out.println("Total is " + subOb.total);
• } }
Method Access in Java

Using super to overcome name hiding.
class A {
int i; }
class B extends A {
int i;
B(int a, int b) {
super.i = a;
i = b; }
void show() {
System.out.println("i in superclass: " + super.i);
System.out.println("i in subclass: " + i);
} }
class UseSuper {
B subOb = new B(1, 2);
subOb.show();
} }2/3/2015 Object Oriented Programming using JAVA 84
A second use of Super

• class A {
• A() {
• System.out.println("Inside A's constructor.");
• } }
• B() {
• System.out.println("Inside B's constructor.");
• } }
• class C extends B {
• C() {
• System.out.println("Inside C's constructor.");
• } }
• class CallingCons {
• C c = new C();
• } }
Constructor in Inheritance

class A {
int i, j;
A(int a, int b) {
i = a; j = b; }
void show() {
System.out.println("i and j: " + i + " " + j); } }
class B extends A {
int k;
B(int a, int b, int c) {
super(a, b);
k = c; }
void show() {
System.out.println("k: " + k); } }
class Override {
B subOb = new B(1, 2, 3);
subOb.show();
} }
Method Overriding

Continue..
If you want to access super class variable you can access using super.
• int k;
• B(int a, int b, int c) {
• super(a, b);
• k = c;
• }
• void show() {
• super.show();
• System.out.println("k: " + k);
• }
• }

• abstract class A {
• abstract void callme();
• void callmetoo() {
• System.out.println("This is a concrete method.");
• } }
• void callme() {
• System.out.println("B's implementation of callme.");
• } }
• class AbstractDemo {
• B b = new B();
• b.callme();
• b.callmetoo();
• } }
Object Oriented Programming using JAVA 88
Using Abstract Classes

• An exception is an abnormal condition that arises
in a code sequence at run time. In other words,
an exception is a run-time error.
• In computer languages that do not support
exception handling, errors must be checked and
handled manually.
• Java’s exception handling avoids these problems
and, in the process, brings run-time error
management into the object oriented world.
Exception Handling

• Java exception handling is managed via five keywords: try, catch, throw,
throws, and finally.
• Program statements that you want to monitor for exceptions are
contained within a try block.
• If an exception occurs within the try block, it is thrown. Your code can
catch this exception (using catch) and handle it in some rational manner.
• System-generated exceptions are automatically thrown by the Java run-
time system. To manually throw an exception, use the keyword throw.
• Any exception that is thrown out of a method must be specified as such
by a throws clause.
• Any code that absolutely must be executed after a try block completes is
put in a finally block.
Exception Handling continue..

try {
// block of code to monitor for errors
}
catch (ExceptionType1 exOb) {
// exception handler for ExceptionType1
}
catch (ExceptionType2 exOb) {
// exception handler for ExceptionType2
}
// ...
finally {
// block of code to be executed after try block ends
}
Exception Handling Syntax

All exception types are subclasses of the built-in
class Throwable. It includes
Exception: This class is used for exceptional
conditions that user programs should catch. This
is also the class that you will subclass to create
your own custom exception types.
Runtime Exception: Exceptions of this type are
automatically defined for the programs that you
write and include things such as division by zero
and invalid array indexing
Exception Types

class Exc {
int d, a;
try {
d = 0;
a = 42 / d;
System.out.println("This will not be printed.");
} catch (ArithmeticException e) {
System.out.println("Division by zero.");
}
System.out.println("After catch statement.");
}
}
Run Time Exception Example

class MultiCatch {
try {
int a = 0;
System.out.println("a = " + a);
int b = 42 / a;
int c[] = { 1 };
c[42] = 99;
} catch(ArithmeticException e) {
System.out.println("Divide by 0: " + e);
} catch(ArrayIndexOutOfBoundsException e) {
System.out.println("Array index oob: " + e);
}
System.out.println(“exception found");
}
}
Multiple Catch Clauses

class NestTry {
try {
int a = 0;
int b = 42 / a;
System.out.println("a = " + a);
try {
if(a==1) a = a/(a-a);
if(a==2) {
int c[] = { 1 };
c[42] = 99;
}} catch(ArrayIndexOutOfBoundsException e) {
System.out.println("Array index out-of-bounds: " + e);
}} catch(ArithmeticException e) {
System.out.println("Divide by 0: " + e);
}}}
Multiple try Statement

It is possible for your program to throw an
exception explicitly, using the throw statement.
The general form of throw is shown here:
throw ThrowableInstance;
new is used to construct an object of exception.
e.g. To create a exception for Null pointer we will
declare as in try block:
throw new NullPointerException("demo");
Use of throw

class ThrowDemo {
static void exception() {
try {
throw new NullPointerException("demo");
} catch(NullPointerException e) {
System.out.println("Caught inside demoproc.");
throw e;
} }
try {
exception();
} catch(NullPointerException e) {
System.out.println("Recaught: " + e);
}}}
Use of throw example

class ThrowsDemo {
static void throwOne() throws IllegalAccessException {
System.out.println("Inside throwOne.");
throw new IllegalAccessException("demo");
}
try {
throwOne();
} catch (IllegalAccessException e) {
System.out.println("Caught " + e);
}}}
Use of throws

• finally creates a block of code that will be
executed after a try/catch block has completed
and before the code following the try/catch
block. The finally block will execute whether or
not an exception is thrown.
• This can be useful for closing file handles and
freeing up any other resources that might have
been allocated at the beginning of a method.
• The finally clause is optional. However, each try
statement requires at least one catch or a finally
clause.
finally

class FinallyDemo {
static void procA() {
try {
System.out.println("inside procA");
throw new RuntimeException("demo");
} finally {
System.out.println("procA's finally");
}}
static void procB() {
try {
System.out.println("inside procB");
return;
} finally {
System.out.println("procB's finally");
} }
Finally with example

static void procC() {
try {
System.out.println("inside procC");
} finally {
System.out.println("procC's finally");
} }
try {
procA();
} catch (Exception e) {
System.out.println("Exception caught");
}
procB();
procC(); } }
Finally with example continue..

• Scanner reads formatted input and converts it
into its binary form.
• Scanner can be used to read input from the
console, a file, a string, or any source that user
gives on runtime.
• To define scanner class
• Scanner name= new Scanner(System.in);
Use of hasNext()
Scanner classes

Scanner classe Example
else {
String str = conin.next();
if(str.equals("done")) break;
else {
System.out.println("Data format error.");
return;
}
}
}
System.out.println("Average is " + sum / count);
}
}
import java.util.*;
class AvgNums {
public static void main(String
args[]) {
Scanner conin = new
Scanner(System.in);
int count = 0;
double sum = 0.0;
System.out.println("Enter
numbers to average.");
while(conin.hasNext()) {
if(conin.hasNextDouble()) {
sum += conin.nextDouble();
count++;
}

• A string is a sequence of characters.
• Java implements strings as objects of type
Strings.
• Java performs string handling by methods to
compare two string, search for a substring,
concatenate two string, and change the case
of letters within strings.
• String Buffer, String Builder are classes are
defined in java.lang
String Handling

class MakeString {
char c[] = {'J', 'a', 'v', 'a'};
String s1 = new String(c);
String s2 = new String(s1);
System.out.println(s1);
System.out.println(s2);
}
}
String Object creation

• String length: length()
• String concatenation
• String conversion and toString()
• charAt()
• getChars()
• getBytes()
• toCharArray()
• Equals() and equalsIgnoreCase
• compareTo()
• indexOf() & lastIndexOf()
METHODS used in strings

• Substring()
• Concat()
• Replace()
• Trim()
• StringtoLowerCase/StringtoUpperCase
MODIFYING a String

• Length() and capacity
• setLength()
• charAt()& setCharAt()
• getChars()
• Append()
• Insert()
• Reverse()
• Delete() and deleteCharAt()
• Replace()Substring()
String Buffer

Java basic

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (15)

Andere mochten auch

Andere mochten auch (20)

Ähnlich wie Java basic

Ähnlich wie Java basic (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Java basic