Understanding Inheritance in Java

Understanding inheritance with private, public , protected  and default/package access specifier in Java

Public  accessibility modifier rules are same for instance methods and instance variables.

packageA
├── ClientClassAInSamePackage.java
├── SubClassAInSamePackage.java
├── subPackageA
│   ├── ClientClassAinSameSubPackage.java
│   └── SubClassAinSameSubPackage.java
└── SuperClassA.java

packageB
├── ClientClassBInDifferentPackage.java
├── SubClassBInDifferentPackage.java
└── subPackageB
├── ClientClassBInDifferentSubPackage.java
└── SubClassBInDifferentSubPackage.java

 

Is SuperClassA  Accessible :

Package private accessibility public accessibility Protected accessibility Default accessibility
SubClassAInSamePackage No YES YES YES
ClientClassAInSamePackage No YES YES YES
SubClassAinSameSubPackage No YES YES NO
ClientClassAinSameSubPackage No YES NO NO
SubClassBInDifferentPackage No YES YES NO
ClientClassBInDifferentPackage No YES NO NO
SubClassBInDifferentSubPackage No YES YES NO
ClientClassBInDifferentSubPackage No YES NO NO

 

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ChildClass extends from the SuperClass   SubClassAInSamePackage Example :

 

 

package com.big.data.java.packageA;

public class SubClassAInSamePackage extends SuperClassA {

    private int subClassAState = 20;

    //getPrivateState() private method is not visible

    @Override
    public String getPublicState() {
        return "SubClassAInSamePackage value is  " + subClassAState;
    }

    @Override
    protected String getProtectedState() {
        return "SubClassAInSamePackage value is  " + subClassAState;
    }

    @Override
    String getDefaultState() { return "SubClassAInSamePackage value is  " + subClassAState; }

    public static void main(String[] args) {
        // parent refrence pointing to the child class , SuperClassA and SubClassA are in same package
        SuperClassA superVar = new SubClassAInSamePackage();

        System.out.println("Parent class method call output for Public is :  " + superVar.getPublicState());

        System.out.println("Parent class method call output for Protected is :  " + superVar.getProtectedState());

        System.out.println("Parent class method call output for Private is :  " + superVar.getDefaultState());

        // Child refrence pointing to its own object
        SubClassAInSamePackage child = (SubClassAInSamePackage) superVar;
        System.out.println("Child class method call output for Public is  " + child.getPublicState());

        System.out.println("Child class method call output for Protected is  " + child.getProtectedState());

        System.out.println("Child class method call output for Private is  " + child.getDefaultState());

    }
}

 

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Client Class :  uses the reference and object of the SuperClass  Example :

 

package com.big.data.java.packageA;

public class ClientClassAInSamePackage {

    public static void main(String[] args) {

        // accessing superClassA from a client class in the same package as that of the superClass
        SuperClassA superClassA = new SuperClassA();
        // Private is not accessible. 

        System.out.println("Parent class method call output for Public is :  " + superClassA.getPublicState());

        System.out.println("Parent class method call output for Protected is :  " + superClassA.getProtectedState());

        System.out.println("Parent class method call output for Default is :  " + superClassA.getDefaultState());

         //superClassA.getPrivateState() getPrivateState() private method is not visible

    }
}
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