In Java, what’s the difference between method overloading and method overriding?

The difference between overriding and overloading in Java is a common source of confusion – but it is fairly simple to understand. Let’s start the discussion by talking more about method overloading. Overloading in Java can occur when two or more methods in the same class share the same name or even if a child class shares a method with the same name as one of it’s parent classes. But, in order to actually have overloaded methods, the methods not only have to have the same name, but there are other conditions that must be satisfied – read below to see what those conditions are.
Suppose we have a class called TestClass which has 2 methods, and both methods have the same name – let’s say that name is “someMethod” – this would be considered to be method overloading if  
 at least one of these 2 things is true:
1.) The number of parameters is different for the methods   
2.) The parameter types are different.  

How to NOT overload methods:

It’s important to understand that method overloading is NOT something you can accomplish by doing these 2 things:
1.  Changing the return type of the method   
2.  Changing the name of the method parameters, but 
    not changing the parameter types.  
Confused? Well, here are some very helpful examples of where overloading would be both valid and invalid:

Examples of Method Overloading in Java – both valid and invalid:

//compiler error - can't overload based on the   
//type returned -
//(one method returns int, the other returns a float):    

int changeDate(int Year) ;  
float changeDate (int Year);    

//compiler error - can't overload by changing just 
//the name of the parameter (from Month to Year):    

int changeDate(int Month) ;  
float changeDate(int Year);    

//valid case of overloading, since there is an   
//extra parameter in the first method:        

int changeDate(int Year, int Month) ;  
int changeDate(int Year);    

//also a valid case of overloading, since the   
//parameters are of different types:    

int changeDate(float Year) ;  
int changeDate(int Year); 
 
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What about method overriding?

Overriding methods is completely different from overloading methods. If a derived class requires a different definition for an inherited method, then that method can be redefined in the derived class. This would be considered overriding. An overridden method would have the exact same method name, return type, number of parameters, and types of parameters as the method in the parent class, and the only difference would be the definition of the method.
Let’s summarize the differences between overloading and overriding. When overloading, one must change either the type or the number of parameters for a method that belongs to the same class. But, overriding a method means that a method inherited from a base class is what’s being changed.
 

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