package foo;public class Main {    public static void bubbleSort(int[] a, int len) {        int in, out;        for (out = len - 1; out > 0; --out) {            for (in = 0; in < out; ++in) {                if (a[in] > a[in+1]) {                    swap(a, in, in + 1);                }            }        }    }    public static void swap(int[] a, int index1, int index2) {        int temp = a[index1];        a[index1] = a[index2];        a[index2] = temp;    }    public static void main(String[] args) {        int[] a = new int[] {3, 2, 1, 5, 4};        bubbleSort(a, a.length);    }}

冒泡排序的效率O（N*N），比较N*N/2，交换N*N/4