比较2D阵列

Question

Im trying to compare two 2D arrays by using this. But I keep getting " Arrays are not the same. " even when they are the same.

     int i;
     int j = 0;
     int k;
     int l;

List<Integer> list = new ArrayList<Integer>();
List<Integer> list1 = new ArrayList<Integer>();
List<Integer> zero = new ArrayList<Integer>();

 for ( i = 1; i <= 16; i++) {
    list.add(i);


}

//System.out.println(list); //[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
Collections.shuffle(list.subList(1, 15));
System.out.println(list);

Collections.replaceAll(list, 16, 0);
   System.out.println(list);


// System.out.println(list); //[11, 5, 10, 9, 7, 0, 6, 1, 3, 14, 2, 4, 15, 13, 12, 8]

int[][] a2 = new int[4][4];
int [][] a3 = new int[4][4];
for ( i = 0; i < 4; i++) {
    for ( j = 0;  j< 4; j++) {


        a2[i][j] = list.get(i*4 + j);
        a3[i][j] = list.get(i*4 + j);
    }

}
for (int[] row : a2) {
System.out.print("[");
for (   int a : row)
    System.out.printf("%4d", a);
System.out.println("]");
}
for (int[] row : a3) {
System.out.print("[");
for (   int a : row)
    System.out.printf("%4d", a);
System.out.println("]");
}
 boolean check1 = Arrays.equals(a2, a3);
if(check1 == false)
System.out.println("Arrays are not same.");
else
System.out.println("Both Arrays are same.");

I can't do it like this either. boolean check1 = Arrays.equals(a2[i][j], a3[i][j]);

Answer 1

The first one does not work because a two-D int array is really an array of arrays (that is, an array of objects). The Arrays.equals() method for an array of objects uses equals() to test whether corresponding elements are equal. Unfortunately for your code, equals() for arrays is the default Object implementation: they are equal() only if they are the identical object. In your case, they are not.

In the second case, when you code Arrays.equals and pass two int values, the compiler can't match it to any signature of the Arrays class.

One way to check equality is to use deepEquals:

boolean check1 = Arrays.deepEquals(a2, a3);

Another way is to iterate the outer array explicitly:

boolean check1 = true;
for (int i = 0; check1 && i < a2.length; ++i) {
    check1 = Arrays.equals(a2[i], a3[i]);
}

Answer 2

boolean check1 = Arrays.deepEquals(a2, a3);

is definitely a possibility. The implementation of that uses Object[] , which may be appealing to you because it checks the types of the arrays you pass on-the-fly.

But if you want stronger typing and a little less overhead, you can write your own as follows.

import java.util.Arrays;

/**
 * Operations on multi-dimensional arrays.
 * 
 * @author stephen harrison
 */
public class ArrayUtils {
    private ArrayUtils() {
        // Static methods only
    }

    public static <T> boolean equals(final T[][] a, final T[][] b) {
        if (a == b) {
            return true;
        }

        if (a == null || b == null) {
            return false;
        }

        if (a.length != b.length) {
            return false;
        }

        for (int i = 0; i < a.length; ++i) {
            if (!Arrays.equals(a[i], b[i])) {
                return false;
            }
        }

        return true;
    }

    public static <T> boolean equals(final T[][][] a, final T[][][] b) {
        if (a == b) {
            return true;
        }

        if (a == null || b == null) {
            return false;
        }

        if (a.length != b.length) {
            return false;
        }

        for (int i = 0; i < a.length; ++i) {
            if (!equals(a[i], b[i])) {
                return false;
            }
        }

        return true;
    }
}

The first equals on 2D arrays calls Arrays.equals() . The 3D version similarly calls the 2D one.

I hope that helps.