What is the process of defining more than one method in a class with the same name but different number or type of parameters?

Overloading occurs when two or more methods in one class have the same method name but different parameters.

Overriding occurs when two methods have the same method name and parameters. One of the methods is in the parent class, and the other is in the child class. Overriding allows a child class to provide the specific implementation of a method that is already present in its parent class.​

The two examples below illustrate their differences:

The table below highlights their key differences:

• Must have at least two methods by the same name in the class.

• Must have a different number of parameters.

• If the number of parameters is the same, then it must have different types of parameters.

• Overloading is known as compile-time polymorphism.

• Must have at least one method by the same name in both parent and child classes.

• Must have the same number of parameters.

• Must have the same parameter types.

• Overriding is known as runtime polymorphism​.

Take a look at the code below:

class Dog{

public void bark(){

System.out.println("woof ");

}

}

class Hound extends Dog{

public void sniff(){

System.out.println("sniff ");

}

public void bark(){

System.out.println("bowl");

}

}

class OverridingTest{

public static void main(String [] args){

Dog dog = new Hound();

dog.bark();

}

}

In this overriding example, the dog variable is declared to be a Dog. During compile-time, the compiler checks if the Dog class has the bark() method. As long as the Dog class has the bark() method, the code compiles. At run-time, a Hound is created and assigned to dog, so, ​ it calls the bark() method of Hound.

Take a look at the code below:

class Dog{

public void bark(){

System.out.println("woof ");

}

//overloading method

public void bark(int num){

for(int i=0; i<num; i++)

System.out.println("woof ");

}

}

In this overloading example, the two bark methods can be invoked using different parameters. The compiler knows that they are different because they have different method signatures​ (method name and method parameter list).

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Here is an example of a typical method declaration:

public double calculateAnswer(double wingSpan, int numberOfEngines, double length, double grossTons) { //do the calculation here }

The only required elements of a method declaration are the method's return type, name, a pair of parentheses, (), and a body between braces, {}.

More generally, method declarations have six components, in order:

1. Modifiers—such as public, private, and others you will learn about later.
2. The return type—the data type of the value returned by the method, or void if the method does not return a value.
3. The method name—the rules for field names apply to method names as well, but the convention is a little different.
4. The parameter list in parenthesis—a comma-delimited list of input parameters, preceded by their data types, enclosed by parentheses, (). If there are no parameters, you must use empty parentheses.
5. An exception list—to be discussed later.
6. The method body, enclosed between braces—the method's code, including the declaration of local variables, goes here.

Modifiers, return types, and parameters will be discussed later in this lesson. Exceptions are discussed in a later lesson.

Definition: Two of the components of a method declaration comprise the method signature—the method's name and the parameter types.

The signature of the method declared above is:

calculateAnswer(double, int, double, double)

Naming a Method

Although a method name can be any legal identifier, code conventions restrict method names. By convention, method names should be a verb in lowercase or a multi-word name that begins with a verb in lowercase, followed by adjectives, nouns, etc. In multi-word names, the first letter of each of the second and following words should be capitalized. Here are some examples:

run runFast getBackground getFinalData compareTo setX isEmpty

Typically, a method has a unique name within its class. However, a method might have the same name as other methods due to method overloading.

Overloading Methods

The Java programming language supports overloading methods, and Java can distinguish between methods with different method signatures. This means that methods within a class can have the same name if they have different parameter lists (there are some qualifications to this that will be discussed in the lesson titled "Interfaces and Inheritance").

Suppose that you have a class that can use calligraphy to draw various types of data (strings, integers, and so on) and that contains a method for drawing each data type. It is cumbersome to use a new name for each method—for example, drawString, drawInteger, drawFloat, and so on. In the Java programming language, you can use the same name for all the drawing methods but pass a different argument list to each method. Thus, the data drawing class might declare four methods named draw, each of which has a different parameter list.

public class DataArtist { ... public void draw(String s) { ... } public void draw(int i) { ... } public void draw(double f) { ... } public void draw(int i, double f) { ... } }

Overloaded methods are differentiated by the number and the type of the arguments passed into the method. In the code sample, draw(String s) and draw(int i) are distinct and unique methods because they require different argument types.

You cannot declare more than one method with the same name and the same number and type of arguments, because the compiler cannot tell them apart.

The compiler does not consider return type when differentiating methods, so you cannot declare two methods with the same signature even if they have a different return type.

Note: Overloaded methods should be used sparingly, as they can make code much less readable.