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();
}
}
Creating Class with multiple constructors1465
