Sorting 2D Arrays in Java Using Arrays.sort

One way to sort a 2D array based on the values of without implementing your own sorting algorithm is to use the overloaded Arrays#Sort(T[] a, Comparator c) method.

double[][] array = {
        {1, 5},
        {13, 1.55},
        {12, 100.6},
        {12.1, .85}
};

java.util.Arrays.sort(array, new java.util.Comparator() {
    public int compare(double[] a, double[] b) {
        return Double.compare(a[0], b[0]);
    }
});

This method takes a Comparator as its second argument, allowing you to define your own sorting criteria. In this case, the Comparator we've provided compares the first element of each double[] array and returns an integer indicating whether it's less than, greater than, or equal to 0.

Using Lambda Functions in Java 8

Java 8 introduces lambda functions, which provide a concise way to define Comparators. We can rewrite the previous code using a lambda function as follows:

Arrays.sort(array, Comparator.comparingDouble(o -> o[0]));

This lambda function takes a double[] array as its input and returns the value of the first element as a double. By sorting the array using this Comparator, we achieve the desired result.