Java Comparator class to sort arrays

Question

Say, we have the following 2-dimensional array:

int camels[][] = new int[n][2]; 

How should Java Comparator class be declared to sort the arrays by their first elements in decreasing order using Arrays.sort(camels, comparator)? The compare function for reference is:

@Override public int compare(int[] a, int [] b) {     return b[0] - a[0]; } 

Answer 1

[...] How should Java Comparator class be declared to sort the arrays by their first elements in decreasing order [...]

Here's a complete example using Java 8:

import java.util.*;  public class Test {      public static void main(String args[]) {          int[][] twoDim = { {1, 2}, {3, 7}, {8, 9}, {4, 2}, {5, 3} };          Arrays.sort(twoDim, Comparator.comparingInt(a -> a[0])                                       .reversed());          System.out.println(Arrays.deepToString(twoDim));     } } 

Output:

[[8, 9], [5, 3], [4, 2], [3, 7], [1, 2]] 

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For Java 7 you can do:

Arrays.sort(twoDim, new Comparator<int[]>() {     @Override     public int compare(int[] o1, int[] o2) {         return Integer.compare(o2[0], o1[0]);     } }); 

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If you unfortunate enough to work on Java 6 or older, you'd do:

Arrays.sort(twoDim, new Comparator<int[]>() {     @Override     public int compare(int[] o1, int[] o2) {         return ((Integer) o2[0]).compareTo(o1[0]);     } });