Access Modifier Visibility
Modifier
|
Class
|
Package
|
Subclass
|
Everywhere
|
public
|
Yes
|
Yes
|
Yes
|
Yes
|
protected
|
Yes
|
Yes
|
Yes
|
No
|
default
|
Yes
|
Yes
|
No
|
No
|
private
|
Yes
|
No
|
No
|
No
|
public - Members are visible in same class, same package, sub classes and in other classes.
protected - Members are visible in same class, same package, sub classes but not in other classes.
default - Members are visible in same class, same package but not in sub classes and other classes.
private - Members are visible only in same class but not in same package, sub classes and other classes.
Access Modifier Level Applicability
Modifier
|
Member Field
|
Member Method
|
Nested Class
|
Top Level Class
|
public
|
Yes
|
Yes
|
Yes
|
Yes
|
default
|
Yes
|
Yes
|
Yes
|
Yes
|
private
|
Yes
|
Yes
|
Yes
|
No
|
protected
|
Yes
|
Yes
|
Yes
|
No
|
public, default - These modifiers can be applied to members of the class and also to the top class.
private, protected - These modifiers can be applied to member of a class only but not to the top class.
Simple Inheritance
parent.java
package r1;
public class parent
{
int x;
public parent()
{
x=10;
}
public static void main(String args[])
{
parent p = new parent();
System.out.println("parent main x="+p.x);
}
}
Output
parent main x=10
sub1.java
package r1;
public class sub1 extends parent // a subclass of parent
{
sub1()
{
x=20;
}
public static void main(String args[])
{
sub1 s1 = new sub1();
System.out.println("In r1 pckg, sub1 class, main fn, sub1.x = "+s1.x);
}
}
Output
In r1 pckg, sub1 class, main fn, sub1.x = 20
Examples of Access Modifiers
Following are the errors that occurs if access modifiers are not used properly:
private - The field parent.x is not visible
parent.java
package r1;
public class parent
{
private int x; // private access modifier
}
sub1.java
package r1; // same package as the parent
public class sub1 extends parent // a subclass of parent
{
sub1()
{
x=20;
}
public static void main(String args[])
{
sub1 s1 = new sub1();
System.out.println("In r1 pckg, sub1 class, main fn, sub1.x = "+s1.x);
}
}
Output
The field parent.x is not visible
Because: sub1.java is not the same class where x is declared.
Because: sub1.java is not the same class where x is declared.
default - The field parent.x is not visible
parent.java
package r1;
public class parent
{
int x; // no access modifier is default
}
sub2.java
// sub2 class is not part of r1 package
import r1.parent; // so its imported
public class sub2 extends parent // a subclass of parent
{
sub2()
{
x=30;
}
public static void main(String args[])
{
sub2 s2 = new sub2();
System.out.println("In no pckg, sub2 class, main fn, sub2.x = "+s2.x);
}
}
Output
The field parent.x is not visibleBecause: sub2.java is not in the same package of parent where x is declared.
protected - The field parent.x is not visible
parent.java
package r1;
public class parent
{
protected int x; // protected access modifier
}
some1.java
// some1 class is not part of r1 package
import r1.parent;
public class some1 // not a subclass of parent
{
public static void main(String args[])
{
parent p = new parent();
System.out.println("In no pckg, some1 class, main fn, parent.x = "+p.x);
}
}
Output
The field parent.x is not visibleBecause: some1.java is neither in the same package nor in subclass of parent where x is declared.
Nested Class
A nested class has access to all the private members of its enclosing class.
public class parent{ public static void main(String args[]) { sub nestedsub1 = new sub(); int disp = nestedsub1.show(); System.out.println("Access to pvt nested subClass's pvt show() = "+disp); } private static class sub // Nested subclass of parent { private int y; private int show() { y=20; return y; } }} |
public class parent
{
public static void main(String args[])
{
sub nestedsub1 = new sub();
int disp = nestedsub1.show();
System.out.println("Access to pvt nested subClass's pvt show() = "+disp);
}
private static class sub // Nested subclass of parent
{
private int y;
private int show()
{
y=20;
return y;
}
}
}
The parent class has access to all members of the nested sub class even private members like show() method
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