Method Overloading in java

When a class has more than one method with same name, then we call that method is overloaded. The overloaded methods will have different number of arguments or different types of arguments, but name of the methods remains same.

Compiler checks method signature for duplicate methods or for method overloading. method signature consist of three things,

 1) Method Name   

 2) Number Of Arguments  

 3) Types of arguments.

If these three things are same for any two methods in a class, then compiler gives duplicate method error.

Compiler first checks method name. If it is same, then it checks number of arguments. If methods differs in number of arguments, then it does not check types of argument. It treats as methods are overloaded. If number of arguments are same then compiler checks types of arguments. If types of arguments are also same, then compiler will give duplicate method error. If types of arguments are not same, then compiler will treat them as methods are overloaded.
For method overloading to be successful, method name must be same and methods must have different number of arguments or different types of arguments. If method names are different, then those methods will be treated as two different methods.
Go through this example,

public class MethodOverloading
{
void methodOverloaded()
{
//No argument method
}
void methodOverloaded(int i)
{
//One argument is passed
}
void methodOverloaded(double d)
{
//One argument is passed but type of argument is different
}
void methodOverloaded(int i, double d)
{
//Two argument method
//Method signature of this method is methodOverloaded(int, double)
}
void methodOverloaded(double d, int i)
{
//It is also two argument method but type of arguments changes
//Method signature of this method is methodOverloaded(double, int)
}
void methodOverloaded(double d1, int i1)
{
                //It has same method signature methodOverloaded(double, int) as of above method
//So, it is a Duplicate method, You will get compile time error here
}
    void differentMethod()
{
//Different method
}
}

Overloaded methods may have same return types or different return types. It does not effect method overloading.

public class MethodOverloading
{
void methodOverloaded()
{
//No argument method, return type is void
}
int methodOverloaded(int i)
{
        //Returns int type
return i;
}
int methodOverloaded(double d)
{
        //Same return type as of above method
return 0;
}
void methodOverloaded(double d)
{
//Duplicate method because it has same method signature as of above method
}
}

Important Note :

 If two methods have same signature and different return types, then those methods will not be treated as two different methods or methods overloaded. For duplication, compiler checks only method signature not return types. If method signature is same, straight away it gives duplicate method error.
Overloaded methods may have same access modifiers or different access modifiers. It also does not effect method overloading.

public class MethodOverloading
{
private void methodOverloaded()
{
//No argument, private method
}
private int methodOverloaded(int i)
{
//One argument private method
return i;
}
protected int methodOverloaded(double d)
{
//Protected Method
return 0;
}
public void methodOverloaded(int i, double d)
{
//Public Method
}
}

Overloaded methods may be static or non-static. This also does not effect method overloading.

public class MethodOverloading
{
private static void methodOverloaded()
{
//No argument, private static method
}
private int methodOverloaded(int i)
{
//One argument private non-static method
return i;
}
static int methodOverloaded(double d)
{
//static Method
return 0;
}
public void methodOverloaded(int i, double d)
{
//Public non-static Method
}
}

From the above examples, it is clear that compiler will check only method signature for method overloading or for duplicate methods. It does not check return types, access modifiers and static or non-static.