Method Overriding

1. Method Overriding

2. Method Overriding
 If a method of the subclass has the same
signature(name and parameter list) and return type
as that of the method in super class then we say that
the methods are overrided.
 The process is known as “Method Overriding”
 The ability of a subclass to override a method allows
a class to modify behavior as needed.
 It is also a method of implementing
“polymorphism”

3. Example
public Class OverrideSuper
{
void test( )
{
System.out.println(“No parameters”);
}
void test(int a)
{
System.out.println(“a: ”+a);
}
}

4. Example cont..
public Class OverrideSub extends OverrideSuper
{
void test( )
{
int x,y,z;
x=10;
y=20;
z=x+y;
System.out.println(z);
}
void test(int a)
{
a=a+10;
System.out.println(“a: ”+a);
}
}

5. Example Cont..
public class OverrideDriver
{
public static void main(String args[])
{
OverrideSuper o=new OverrideSuper( );
o.test( );
o.test(10);
OverrideSub s=new OverrideSub( );
s.test( );
s.test(10);
}
}

6. Accessing Super class Members
 If your method overrides one of its superclass's
methods, you can invoke the overridden method
through the use of the keyword super.

7. Example
public Class OverrideSuper
{
void test( )
{
System.out.println(“No parameters”);
}
void test(int a)
{
System.out.println(“a: ”+a);
}
}

8. Example cont..
public Class OverrideSub extends OverrideSuper
{
void test( )
{
super.test();
int x,y,z;
x=10;
y=20;
z=x+y;
System.out.println(z);
}
void test(int a)
{
super.test(20);
a=a+10;
System.out.println(“a: ”+a);
}
}

9. Example cont..
public class OverrideDriver
{
public static void main(String args[])
{
OverrideSuper o=new OverrideSuper( );
o.test( );
o.test(10);
OverrideSub s=new OverrideSub( );
s.test( );
s.test(10);
}
}

10. Accessing Super class Data Members
 Like methods we can have data members in the
subclass having the same name as that of the super
class.
 Use super keyword to access the data members as
well.
 Example: super.datamember_name

11. Example
public Class OverrideSuper
{
int b;
void test( )
{
System.out.println(“No parameters”);
}
void test(int a)
{
System.out.println(“a: ”+a);
}
}

12. Example cont..
public Class OverrideSub extends OverrideSuper
{
int b;
void test( )
{
super.test();
int x,y,z;
x=10;
y=20;
z=x+y;
System.out.println(z);
}
void test(int a)
{
super.test(20);
super.b=30;
a=a+10;
System.out.println(“a: ”+a);
System.out.println(“b: ”+super.b);
}
}

13. Example cont..
public class OverrideDriver
{
public static void main(String args[])
{
OverrideSuper o=new OverrideSuper( );
o.test( );
o.test(10);
OverrideSub s=new OverrideSub( );
s.test( );
s.test(10);
}
}

14. Lab Task
 Use the following class hierarchy:
Shape
Circle Square Triangle
• All of the classes contain a method known as printValues.
• The printValues method of the sub class should call the method of the super
class.
• Note: Use the classes that you have coded in the previous lab.

15. Calling constructor of the super class
 The syntax for calling a superclass constructor is
 super();
 super(parameter list);
 With super(), the superclass no-argument
constructor is called. With super(parameter list),
the superclass constructor with a matching
parameter list is called.
 Note: Invocation of a superclass constructor
must be the first line in the subclass
constructor.

16. Example
public Class OverrideSuper
{
int b;
OverrideSuper( )
{
System.out.println(“super class”);
}
OverrideSuper(int a)
{
b=a;
System.out.println(“b: ”+b);
System.out.println(“super class”);
}
}

17. Example cont..
public Class OverrideSub extends OverrideSuper
{
int c;
OverrideSub( )
{
super();
c=20;
System.out.println(“sub class”);
}
OverrideSub (int a)
{
super(20);
c=a;
System.out.println(“sub class”);
}
}

18. Example cont..
public class OverrideDriver
{
public static void main(String args[])
{
OverrideSuper o=new OverrideSuper( );
OverrideSuper o=new OverrideSuper(30 );
OverrideSub s=new OverrideSub( );
OverrideSub s=new OverrideSub(40 );
}
}

19. Lab Task 2
 Add call to the super class constructor in all the sub
class constructors.