Recipe 5.10 Operating on a Series of Integers

Problem

You need to work on a range of integers.

Solution

For a contiguous set, use a for loop.

Discussion

To process a contiguous set of integers, Java provides a for loop.^[3] Loop control for the for loop is in three parts: initialize, test, and change. If the test part is initially false, the loop will never be executed, not even once.

^[3] If the set of numbers is in an array or collection (see Chapter 7), use a "foreach" loop (see Recipe 8.2).

For discontinuous ranges of numbers, use a java.util.BitSet .

The following program demonstrates all of these techniques:

import java.util.BitSet; /** Operations on series of numbers */ public class NumSeries {     public static void main(String[] args) {         // When you want an ordinal list of numbers, use a for loop         // starting at 1.         for (int i = 1; i <= months.length; i++)             System.out.println("Month # " + i);              // When you want a set of array indexes, use a for loop         // starting at 0.         for (int i = 0; i < months.length; i++)             System.out.println("Month " + months[i]);         // For a discontiguous set of integers, try a BitSet         // Create a BitSet and turn on a couple of bits.         BitSet b = new BitSet( );         b.set(0);    // January         b.set(3);    // April         // Presumably this would be somewhere else in the code.         for (int i = 0; i<months.length; i++) {             if (b.get(i))                 System.out.println("Month " + months[i] + " requested");         }     }     /** The names of the months. See Dates/Times chapter for a better way */     protected static String months[] = {         "January", "February", "March", "April",         "May", "June", "July", "August",         "September", "October", "November", "December"     }; }