METHODS - Introduction to Java Programming: Comprehensive Version - page 204

6.1 Introduction
Methods can be used to define reusable code and organize and simplify coding.

Key
Point

Suppose that you need to find the sum of integers from 1 to 10 , from 20 to 37 , and from 35
to 49 , respectively. You may write the code as follows:

problem

int sum = 0 ;
for ( int i = 1 ; i <= 10 ; i++)
sum += i;
System.out.println( "Sum from 1 to 10 is " + sum);

sum = 0 ;
for ( int i = 20 ; i <= 37 ; i++)
sum += i;
System.out.println( "Sum from 20 to 37 is " + sum);

sum = 0 ;
for ( int i = 35 ; i <= 49 ; i++)
sum += i;
System.out.println( "Sum from 35 to 49 is " + sum);

You may have observed that computing these sums from 1 to 10 , from 20 to 37 , and from
35 to 49 are very similar except that the starting and ending integers are different. Wouldn't
it be nice if we could write the common code once and reuse it? We can do so by defining a
method and invoking it.
The preceding code can be simplified as follows:

why methods?

1 public static int sum( int i1, int i2) {
2 int result = 0 ;
3 for ( int i = i1; i <= i2; i++)
4 result += i;
5
6

define sum method

return result;

7 }
8
9 public static void main(String[] args) {
10 System.out.println( "Sum from 1 to 10 is " + sum( 1 , 10 ));
11 System.out.println( "Sum from 20 to 37 is " + sum( 20 , 37 ));
12 System.out.println( "Sum from 35 to 49 is " + sum( 35 , 49 ));
13 }

main method
invoke sum

Lines 1-7 define the method named sum with two parameters i1 and i2 . The statements in
the main method invoke sum(1, 10) to compute the sum from 1 to 10 , sum(20, 37) to
compute the sum from 20 to 37 , and sum(35, 49) to compute the sum from 35 to 49 .
A method is a collection of statements grouped together to perform an operation. In earlier chap-
ters you have used predefined methods such as System.out.println , System.exit , Math
.pow , and Math.random . These methods are defined in the Java library. In this chapter, you will
learn how to define your own methods and apply method abstraction to solve complex problems.

method

6.2 Defining a Method
A method definition consists of its method name, parameters, return value type, and body.

Key
Point

The syntax for defining a method is as follows:

modifier returnValueType methodName(list of parameters) {
// Method body;
}