交换方法，以数组和数组的两个整数索引为参数

Question

The following code is for a quick sort class. Towards the bottom, there is a method called swap which is supposed to take an array and swap two of the numbers in the array. Is this possible in Java? In other words is it possible to have a method in the format of swap(T[], int, int) that will work in this instance? I hope my question makes sense.

public class QuickSort {

public static <T extends Comparable<T>> void sort(T[] table) {
    quickSort(table, 0, table.length - 1);
}

private static <T extends Comparable<T>> void quickSort(T[] table, int first, int last) {
    if (first < last) {
        int pivIndex = partition(table, first, last);
        quickSort(table, first, pivIndex - 1);
        quickSort(table, pivIndex + 1, last);
    }
}

private static <T extends Comparable<T>> int partition(T[] table, int first, int last) {
    T pivot = table[first];
    int up = first;
    int down = last;
    do {
        while ((up < last) && (pivot.compareTo(table[up]) >= 0)) {
            up++;
        }
        while (pivot.compareTo(table[down]) < 0) {
            down--;
        }
        if (up < down) {
            swap(table, up, down);
        } 
    }

    while (up < down);
    swap(table, first, down);
    return down;
}

Answer 1

Yes, you can do this, because in Java an Array is an Object, so when you pass it, you're really passing its address in memory. The called function can then operate on it, and those changes will be reflected everywhere.

You might be thinking of something you can do in C++ that you can't do in java, which is swap(int x, int y) . Because primitive data values in java don't have addresses (not ones that are available to the programmer, anyway), there's no way to pass their addresses off so they can be modified non-locally.

Does that make sense?