Creating Multidimensional Arrays

package com.bruceeckel;
 
//: c04:MultiDimArray.java
//Creating multidimensional arrays.
//From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
//www.BruceEckel.com. See copyright notice in CopyRight.txt.
 
import java.util.Random;
 
public class MultiDimArray {
 
    static Random rand = new Random();
 
    public static void main(String[] args) {
	int[][] a1 = { { 1, 2, 3, }, { 4, 5, 6, }, };
	for (int i = 0; i < a1.length; i++)
	    for (int j = 0; j < a1[i].length; j++)
		System.out.println("a1[" + i + "][" + j + "] = " + a1[i][j]);
	// 3-D array with fixed length:
	int[][][] a2 = new int[2][2][4];
	for (int i = 0; i < a2.length; i++)
	    for (int j = 0; j < a2[i].length; j++)
		for (int k = 0; k < a2[i][j].length; k++)
		    System.out.println("a2[" + i + "][" + j + "][" + k + "] = " + a2[i][j][k]);
	// 3-D array with varied-length vectors:
	int[][][] a3 = new int[rand.nextInt(7)][][];
	for (int i = 0; i < a3.length; i++) {
	    a3[i] = new int[rand.nextInt(5)][];
	    for (int j = 0; j < a3[i].length; j++)
		a3[i][j] = new int[rand.nextInt(5)];
	}
	for (int i = 0; i < a3.length; i++)
	    for (int j = 0; j < a3[i].length; j++)
		for (int k = 0; k < a3[i][j].length; k++)
		    System.out.println("a3[" + i + "][" + j + "][" + k + "] = " + a3[i][j][k]);
	// Array of nonprimitive objects:
	Integer[][] a4 = { { new Integer(1), new Integer(2) }, { new Integer(3), new Integer(4) }, { new Integer(5), new Integer(6) }, };
	for (int i = 0; i < a4.length; i++)
	    for (int j = 0; j < a4[i].length; j++)
		System.out.println("a4[" + i + "][" + j + "] = " + a4[i][j]);
	Integer[][] a5;
	a5 = new Integer[3][];
	for (int i = 0; i < a5.length; i++) {
	    a5[i] = new Integer[3];
	    for (int j = 0; j < a5[i].length; j++)
		a5[i][j] = new Integer(i * j);
	}
	for (int i = 0; i < a5.length; i++)
	    for (int j = 0; j < a5[i].length; j++)
		System.out.println("a5[" + i + "][" + j + "] = " + a5[i][j]);
	// Output test
	int ln = 0;
	for (int i = 0; i < a3.length; i++)
	    for (int j = 0; j < a3[i].length; j++)
		for (int k = 0; k < a3[i][j].length; k++)
		    ln++;
 
    }
}