This program is a demonstration of how to correctly declare loop variables for for-loops.

ForLoopIndexDemo.java

/**
 * This class is a demo of how to implement for-loops correctly, declaring the loop variables
 * inside of the for-loops, to limit their scope so that the loop variables can't be used outside
 * of the loop where the values are too big to be valid array indexes and an ArrayIndexOutOfBoundsException
 * is thrown.
 * 
 * @author kaydell
 *
 */
public class ForLoopIndexDemo {
  
	/**
	 * This method demonstrates the right way to declare the loop variable called "i".
	 */
	private static void runGoodLoop() {
		int[] array = { 1, 2, 3 };
		for (int i = 0; i < array.length; i++) {
			System.out.println(array[i]);
		}
		// i is defined inside of the for-loop, you can't use it outside of the for-loop, which is good
		// System.out.println(array[i]); // This won't compile.  array[i] would throw an exception anyways
	}
	
	/**
	 * This method demonstrates the wrong way to declare the loop variable called "i".
	 * Running this method will throw an ArrayIndexOutOfBoundsException.
	 */
	private static void runBadLoop() {
		int[] array = { 1, 2, 3 };
		int i;
		for (i = 0; i < array.length; i++) {
			System.out.println(array[i]);
		}
		System.err.println("An exception will be thrown next");
		System.out.println(array[i]); // This will compile but will throw an exception because after the loop, i is too big
	}

	public static void main(String[] args) {
		runGoodLoop();
		runBadLoop();
	}

}