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Interfaces, Packages and Access Control >
Siva Nookala - 03 Mar 2017
Access Control Example included from the book 'Java - The Complete Reference' Eighth Edition, demonstrates the various levels of access.

// File : p1\Protection.java

package p1;

class Protection
{
    int n = 1;
    private int n_pri = 2;
    protected int n_pro = 3;
    public int n_pub = 4;

    public Protection()
    {
        System.out.println("base constructor");
        System.out.println("n = " + n);
        System.out.println("n_pri = " + n_pri);
        System.out.println("n_pro = " + n_pro);
        System.out.println("n_pub = " + n_pub);
    }
}
// File : p1\Derived.java

package p1;

class Derived extends Protection
{
    public Derived()
    {
        System.out.println("derived constructor");
        System.out.println("n = " + n);
        // System.out.println("n_pri = " + n_pri); // WILL NOT WORK
        System.out.println("n_pro = " + n_pro);
        System.out.println("n_pub = " + n_pub);
    }
}
// File : p1\SamePackage.java

package p1;

class SamePackage
{
    public SamePackage()
    {
        Protection p = new Protection();

        System.out.println("same package constructor");
        System.out.println("n = " + p.n);
        // System.out.println("n_pri = " + p.n_pri); // WILL NOT WORK
        System.out.println("n_pro = " + p.n_pro);
        System.out.println("n_pub = " + p.n_pub);
    }
}
// File : p2\Protection2.java

package p2;

class Protection2 extends p1.Protection
{
    public Protection2()
    {
        System.out.println("derived other package constructor");
        // System.out.println("n = " + n); // WILL NOT WORK
        // System.out.println("n_pri = " + n_pri); // WILL NOT WORK
        System.out.println("n_pro = " + n_pro);
        System.out.println("n_pub = " + n_pub);
    }
}
// File : p2\OtherPackage.java

package p2;

class OtherPackage
{
    public OtherPackage()
    {
        p1.Protection p = new p1.Protection();
        System.out.println("other package constructor");
        // System.out.println("n = " + n); // WILL NOT WORK
        // System.out.println("n_pri = " + n_pri); // WILL NOT WORK
        // System.out.println("n_pro = " + n_pro); // WILL NOT WORK
        System.out.println("n_pub = " + n_pub);
    }
}
If you want try this program, first create the files Protection.java, Derived.java and SamePackage.java in the directory p1 and Protection2.java and OtherPackage.java in the directory p2. Then copy the respective code into those java files.
Create the following Demo.java file to test the classes in package p1.
// File : p1\Demo.java

package p1;

class Demo
{
    public static void main(String s[])
    {
        Protection ob1 = new Protection();
        Derived ob2 = new Derived();
        SamePackage ob3 = new SamePackage();
    }
}

Create the following Demo.java file to test the classes in package p2.
// File : p2\Demo.java

package p2;

class Demo
{
    public static void main(String s[])
    {
        Protection2 ob1 = new Protection2();
        OtherPackage ob2 = new OtherPackage();
    }
}

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