Instance field vs static field - Java Object Oriented Design

Java examples for Object Oriented Design:Field

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Description

Instance field vs static field

Demo Code

import java.util.*;

public class AClass {

    public int instanceInteger = 0;

    public int instanceMethod() {
        return instanceInteger;
    }/*  www . ja  va 2  s.  c  o  m*/

    public static int classInteger = 0;

    public static int classMethod() {
        return classInteger;
    }

    public static void main(String[] args) {
        AClass anInstance = new AClass();
        AClass anotherInstance = new AClass();

        //Refer to instance members through an instance.
        anInstance.instanceInteger = 1;
        anotherInstance.instanceInteger = 2;
        System.out.format("%s%n", anInstance.instanceMethod());
        System.out.format("%s%n", anotherInstance.instanceMethod());

        //Illegal to refer directly to instance members from a class method
        //System.out.format("%s%n", instanceMethod());    //illegal
        //System.out.format("%s%n", instanceInteger);     //illegal

        //Refer to class members through the class...
        AClass.classInteger = 7;
        System.out.format("%s%n", classMethod());

        //...or through an instance.
        System.out.format("%s%n", anInstance.classMethod());

        //Instances share class variables
        anInstance.classInteger = 9;
        System.out.format("%s%n", anInstance.classMethod());
        System.out.format("%s%n", anotherInstance.classMethod());
    }
}

/*
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 *
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 *
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 *
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 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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Result


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