coreJava : Access Modifiers in Java

Access Modifiers in Java

The access modifiers in java specifies scope of a data member, method, constructor or class.

there are 4 types of java access modifiers :

       private

       default

       protected

       public

Understanding all java access modifiers

Let's understand the access modifiers by a simple table.

Access Modifier	within class	within package	outside package	outside package by subclass only
Private	Y	N	N	N
Default	Y	Y	N	N
Protected	Y	Y	N	Y
Public	Y	Y	Y	Y

Access control modifier

Java language has four access modifier to control access levels for classes, variable methods and constructor.

1.Default - Default has scope only inside the same package

2.Public - Public scope is visible everywhere

3.Protected - Protected has scope within the package and all sub classes

4.Private - Private has scope only within the classes

save as A.java

package com.mypack1;

//All data members are accessible within the class.

 public class A {

           

           public int i =10;

           protected int k =11            

           int l=12;

           private int j=13;              

            public void m1(){               }     

            protected void m2(){                    }     

            void m3(){              }     

            private void m4(){    }     

                      

          public static void main(String[] args) {

                   A a1 = new A();

                  

                   a1.m1();a1.m2();a1.m3();a1.m4();

                   System.out.println(a1.i+" "+a1.j+ " "+a1.k+" "+a1.l);

          }

}

save as  C.java

package com.mypack1;

import com.mypack1.*;

//private members are not accessible from other classes.

public class C {

          public static void main(String[] args) {

                  

                  

                   A a1 = new A();

                   a1.m1();

                   a1.m2();

                   a1.m3();

                   // a1.m4();

                   //System.out.println(a1.j);

                   System.out.println(a1.i);              

                   System.out.println(a1.k);

                   System.out.println(a1.l);

          }

}

save as B.java

package com.mypack2;

import com.mypack1.A;

/*  private,default and protected members are not accessible from other packages.

 *  but protected members are accessible from sub class objects.

 *

 */

public class B extends A{

          public static void main(String[] args) {

                   A a1 = new A();

                   a1.m1();                

                   //a1.m2();

                   //a1.m3();

                   // a1.m4();

                   //System.out.println(a1.j);

                   System.out.println(a1.i);              

                   //System.out.println(a1.k);

                   //System.out.println(a1.l);

                   B b1 = new B();

                  

                   b1.m1();                

                   b1.m2();

                   //b1.m3();

                   // b1.m4();

                   //System.out.println(b1.j);

                   System.out.println(b1.i);              

                   System.out.println(b1.k);

                   //System.out.println(b1.l);

          }

}

save as D.java

package com.mypack2;

//  private,default and protected members are not accessible from other packages.

import com.mypack1.A;

public class D {

          public static void main(String[] args) {

                   A a1 = new A();

                   a1.m1();                

                   //a1.m2();

                   //a1.m3();

                   // a1.m4();

                   //System.out.println(a1.j);

                   System.out.println(a1.i);              

                   //System.out.println(a1.k);

                   //System.out.println(a1.l);

          }

}

save as A.java

package com.mypack3;

//All data members are accessible within the class.

 public class A {

            public A(){}

            protected A(int i){}

            A(int i,int j){}

            private A(int i,int j,int k){}

           

          public static void main(String[] args) {

                   A a1 = new A();

                   A a2 = new A(11);

                   A a3 = new A(11,22);

                   A a4 = new A(11,22,33);

                  

          }

}

save as  C.java

package com.mypack3;

import com.mypack3.*;

//private members are not accessible from other classes.

public class C {

          public static void main(String[] args) {

                   A a1 = new A();

                   A a2 = new A(11);

                   A a3 = new A(11,22);

                   //A a4 = new A(11,22,33);

                  

                  

          }

}

save as B.java

package com.mypack4;

import com.mypack3.A;

/*  private,default and protected members are not accessible from other packages.

 *  but protected members are accessible from sub class objects.

 *

 */

public class B extends A{

          B(int i){

                   super(i);

                   }

          public static void main(String[] args) {

                   A a1 = new A();

                   //A a2 = new A(11);

                   //A a3 = new A(11,22);

                   //A a4 = new A(11,22,33);

                  

                   B b1 = new B(11);            

                  

          }

}

save as D.java

package com.mypack4;

//  private,default and protected members are not accessible from other packages.

import com.mypack3.A;

public class D {

          public static void main(String[] args) {

                   A a1 = new A();

                   //A a2 = new A(11);

                   //A a3 = new A(11,22);

                   //A a4 = new A(11,22,33);

                  

                  

          }

}