Chapter 2.3 : Java Class & Object

Class is a template for creating objects which defines its state and behaviour. A class contains field and method to define the state and behavior of its Object. 

Syntax for Declaring Class:

<Access Modifier> class <Class_Name> extends

                 <Super_Class_Name> implements <Interface_Name>

Access modifier define who in java world can access this Class and member of the class.

Class_Name

Unique name for the class in specific package.

Super_Class_Name

Name of class which above class extends.(Super class of the given class)

Interface_Name

Name of Inerface ‘Class_Name‘ class implements.(Implements keyword is used for this purpose)

Internal structure of Class

<Access Modifier> class <Class_Name> extends <Super_Class_Name> implements <Interface_Name>{

    <static initilizar block>

    <ananymous block>

    <constructor declarations>

    <field declarations (Static and Non-Static)>

    <method declarations (Static and Non-Static)>

    <Inner class declarations>

    <nested interface declarations>

    Access variables inside class

}

 

Example of  Java Class

Classes are written in Java source file. A source file can contain more then one Java class. Below are the rules related to Java source code file.

/*

* This is Multi Line Comment and Comment can appear at any place

*/

package com.jbt;

import java.lang.*;

/*

* As this file contains public class. Then the name of this file should be TestClass.java

*/

public class TestClass {

    public int i;

    static {

        System.out.println("This is static block");

    }

    {

        System.out.println("This is ananuymous block");

    }

    TestClass() {

        System.out.println("This is constructor");

    }

    void methid() {

        System.out.println("This is method");

    }

}

class AnotherClass {

}