Differencebetween Method Overloading and Overriding

What is the difference between method overloading and overriding?

Method overloading deals with the notion of having two or more methods in the same class with the same name but different arguments.

void foo(int a)
void foo(int a, float b)

Method overriding means having two methods with the same arguments, but different implementations. One of them would exist in the parent class, while another will be in the derived, or child class. The @Override annotation, while not required, can be helpful to enforce proper overriding of a method at compile time.

class Parent {
    void foo(double d) {
        // do something
    }
}

class Child extends Parent {

    @Override
    void foo(double d){
        // this method is overridden.  
    }
}

How does JVM differentiates between method overloading and method overriding internally?

The JVM only deals with method overriding. A method is overridden by adding a method with the same signature in a derived class (the only allowed difference is in the return type, which is allowed to be more specific). The signature encodes the method's name, as well as the types of the parameters and the return type.

Method overloading means having multiple methods with the same "simple name" but different signatures. At compile time, the javac compiler chooses one of the same-named methods based on the types of the arguments and places its signature in the compiled .class file. A method invocation in compiled Java bytecode must specify the signature of the callee.

Difference between overriding and overloading of a function in C++

overloading means functions with same name having different parameters , it does not really depend whether you are using procedural language or object oriented language you can do overloading. well as far as over riding is concerned it means we are explicitly defining a function that exist in base class in derived class . obviously you need object oriented language to perform over riding as it is done between base and derived classes.

What is function overloading and overriding in php?

Overloading is defining functions that have similar signatures, yet have different parameters. Overriding is only pertinent to derived classes, where the parent class has defined a method and the derived class wishes to override that method.

In PHP, you can only overload methods using the magic method __call.

An example of overriding:

<?php

class Foo {
   function myFoo() {
      return "Foo";
   }
}

class Bar extends Foo {
   function myFoo() {
      return "Bar";
   }
}

$foo = new Foo;
$bar = new Bar;
echo($foo->myFoo()); //"Foo"
echo($bar->myFoo()); //"Bar"
?>

Differentiate between function overloading and function overriding

You are putting in place an overloading when you change the original types for the arguments in the signature of a method.

You are putting in place an overriding when you change the original Implementation of a method in a derived class.

Understanding method overloading and overriding in java

I know method overloading means defining a method in a subclass with the same name as in parent class but with different parameters

Incorrect. A method is overloaded if there is another method with the same name but different signatures in the same class.

Or more specifically I miss understanding or should I say a minimal set of rules which can dictate what will be the output in all examples.

The rules that the compiler and runtime applies when figuring out which method to call is described in section 15.12 of the Java Language Specification. The most relevant subsections to this question are 15.12.1, 15.12.2 and 15.12.4. This answer will essentially be a simplification of what is said there.

There are basically 3 things that the compiler and the runtime needs to decide:

1. Which class should I search in? (compile time)
2. Which overload should I call? (compile time)
3. Which implementation should I call? (runtime)

Step 1 is decided based on the compile time type of the object on which you are calling the method. The class to search is the compile time type of that object.

Step 2 is decided by looking at all the matching overloads found in the class from Step 1, and picking the most specific one.

Step 3 depends on the runtime type.

Let's apply these rules to Example 3, 4 and 5. In all three examples, the class to search is A.

Example 3

Two overloads of method are declared in A. method(A) is overridden in B

• a.method(b);

  Both method(A) and method(B) are applicable here, but method(B) is more specific, so method(B) is chosen in Step 2.

  method(B) is not overridden in B, so in Step 3 the implementation in A is chosen.

• a.method(a);

  Only method(A) is applicable so method(A) is chosen at Step 2, because the compiler doesn't know the runtime type of a. Note that Step 2 is carried out at compile time.

  method(A) is overridden in B, so the implementation in B is chosen in Step 3.

Example 4

Same as Example 3, except that method(B) is also overridden in B, so a.method(b); calls the implementation in B.

Example 5

Only one overload of method is declared in A. B declares 2 overloads. One of them overrides method(A) in A.

Unlike the other examples, in resolving a.method(b);, the compiler can't find a method(B) in A anymore, so the best applicable overload is method(A) in Step 2. And then the implementation in B is chosen in Step 3.

Resolving a.method(b); is similar to Example 4.

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