Java Methods

A Java method is a collection of statements that are grouped together to perform an operation. When you call the System.out.println method, for example, the system actually executes several statements in order to display a message on the console.

Creating a Method:

In general, a method has the following syntax:

modifier returnValueType methodName(list of parameters)

{

// Method body;

}

A method definition consists of a method header and a method body. Here are all the parts of a method:

  • Modifiers: The modifier, which is optional, tells the compiler how to call the method. This defines the access type of the method.
  • Return Type: A method may return a value. The returnValueType is the data type of the value the method returns. Some methods perform the desired operations without returning a value. In this case, the returnValueType is the keyword void.
  • Method Name: This is the actual name of the method. The method name and the parameter list together constitute the method signature.
  • Parameters: A parameter is like a placeholder. When a method is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a method. Parameters are optional; that is, a method may contain no parameters.
  • Method Body: The method body contains a collection of statements that define what the method does.

Note: In certain other languages, methods are referred to as procedures and functions. A method with a nonvoid return value type is called a function; a method with a void return value type is called a procedure.

Example:

Here is the source code of the above defined method called max(). This method takes two parameters num1 and num2 and returns the maximum between the two:

/** Return the max between two numbers */

public static int max(int num1, int num2) {

int result;

if (num1 > num2)

result = num1;

else

result = num2;

 

return result;

}

Calling a Method:

In creating a method, you give a definition of what the method is to do. To use a method, you have to call or invoke it. There are two ways to call a method; the choice is based on whether the method returns a value or not.

When a program calls a method, program control is transferred to the called method. A called method returns control to the caller when its return statement is executed or when its method-ending closing brace is reached.

If the method returns a value, a call to the method is usually treated as a value. For example:

int larger = max(30, 40);

If the method returns void, a call to the method must be a statement. For example, the method println returns void. The following call is a statement:

System.out.println("Welcome to Java!");

Example:

Following is the example to demonstrate how to define a method and how to call it:

public class TestMax {
   /** Main method */
   public static void main(String[] args) {
      int i = 5;
      int j = 2;
      int k = max(i, j);
      System.out.println("The maximum between " + i +
                    " and " + j + " is " + k);
   }

   /** Return the max between two numbers */
   public static int max(int num1, int num2) {
      int result;
      if (num1 > num2)
         result = num1;
      else
         result = num2;

      return result; 
   }
}

This would produce following result:

The maximum between 5 and 2 is 5

This program contains the main method and the max method. The main method is just like any other method except that it is invoked by the JVM.

 

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