Overriding in Java

Method Overriding in Java

Whenever same method name is existing in both base class and derived class with same types of parameters or same order of parameters is known as method Overriding. Here we will discuss about Overriding in Java.

Advantage of Java Method Overriding

• Method Overriding is used to provide specific implementation of a method that is already provided by its super class.
• Method Overriding is used for Runtime Polymorphism

Rules for Method Overriding

• Method must have same name as in the parent class.
• Method must have same parameter as in the parent class.
• Must be IS-A relationship (inheritance).
• The data types of the arguments along with their sequence must have to be preserved as it is in the overriding method.
• Any method which is overriding can throw any unchecked exceptions, in spite of whether the overridden method usually method of parent class might throw an exception or not.
• The private, static and final methods can't be overridden as they are local to the class.

Understanding the problem without method overriding

Lets understand the problem that we may face in the program if we do not use method overriding.

class Walking
{  
void walk()
{
System.out.println("Man walking fastly");
}  
}  
class OverridingDemo
{  
public static void main(String args[])
{  
Walking obj = new Walking();  
obj.walk();  
}
}

Man walking

Problem is that I have to provide a specific implementation of walk() method in subclass that is why we use method overriding.

Example of method overriding in Java

In this example, we have defined the walk method in the subclass as defined in the parent class but it has some specific implementation. The name and parameter of the method is same and there is IS-A relationship between the classes, so there is method overriding.

class Walking
{  
void walk()
{
System.out.println("Man walking fastly");
}  
}  
class Man extends walking
{  
void walk()
{
System.out.println("Man walking slowly");
}
}

class OverridingDemo
{  
public static void main(String args[])
{  
Walking obj = new Walking();  
obj.walk();  
}
}

Man walking slowly

Note: Whenever we are calling overridden method using derived class object reference the highest priority is given to current class (derived class). We can see in the above example high priority is derived class.

Note: super. (super dot) can be used to call base class overridden method in the derived class.

class A
{
int x;
void f1()
{
x=10;
System.out.println(x);
}
void f4()
{
System.out.println("this is f4()");
System.out.println("-----------------");
}
};
class B extends A
{
int y;
void f1()
{
int y=20;
System.out.println(y);
System.out.println("this is f1()");
System.out.println("------------------");
}
};
class C extends A
{
int z;
void f1()
{
z=10;
System.out.println(z);
System.out.println("this is f1()");
}
};
class Overide
{
public static void main(String[] args)
{
A a1=new B();
a1.f1();
a1.f4();
A c1=new C();
c1.f1();
c1.f4();
}
}

class Person
{
String name;
void sleep(String name)
{
this.name=name;
System.out.println(this.name +"is sleeping+8hr/day");
}
void walk()
{
System.out.println("this is walk()");
System.out.println("-----------------");
}
};
class Student extends Person
{
void writExams()
{
System.out.println("only student write the exam");
}
void sleep(String name)
{
super.name=name;
System.out.println(super.name +"is sleeping 6hr/day");
System.out.println("------------------");
}
};
class Developer extends Person
{
public void designProj()
{
System.out.println("Design the project");
}
void sleep(String name)
{
super.name=name;
System.out.println(super.name +"is sleeping 4hr/day");
System.out.println("------------------");
}
};
class OverideDemo
{
public static void main(String[] args)
{
Student s1=new Student();
s1.writExams();
s1.sleep("student");
s1.walk();
Developer d1=new Developer();
d1.designProj();
d1.sleep("developer");
}
}

Difference between Overloading and Overriding

Note: In overloading we have to check only methods names (must be same) and arguments types (must be different) except these the remaining like return type access modifiers etc. are not required to check
But in overriding every things check like method names arguments types return types access modifiers etc.