选择排序（java）

package class01;

import java.util.Arrays;

public class Code04_SelectionSort {

public static void selectionSort(int[] arr) {
	if (arr == null || arr.length < 2) {
		return;
	}
	for (int i = 0; i < arr.length - 1; i++) { 
		int minIndex = i;
		for (int j = i + 1; j < arr.length; j++) {
			if(arr[j] < arr[minIndex]) {
				minIndex = j;
			}
		}
		swap(arr, i, minIndex);
	}
}

public static void swap(int[] arr, int i, int j) {
	int tmp = arr[i];
	arr[i] = arr[j];
	arr[j] = tmp;
}

// for test
public static void comparator(int[] arr) {
	Arrays.sort(arr);
}

// for test
public static int[] generateRandomArray(int maxSize, int maxValue) {
	// Math.random() [0,1)
	// Math.random() * N [0,N)
	// (int)(Math.random() * N) [0, N-1]
	int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
	for (int i = 0; i < arr.length; i++) {
		// [-? , +?]
		arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
	}
	return arr;
}

// for test
public static int[] copyArray(int[] arr) {
	if (arr == null) {
		return null;
	}
	int[] res = new int[arr.length];
	for (int i = 0; i < arr.length; i++) {
		res[i] = arr[i];
	}
	return res;
}

// for test
public static boolean isEqual(int[] arr1, int[] arr2) {
	if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
		return false;
	}
	if (arr1 == null && arr2 == null) {
		return true;
	}
	if (arr1.length != arr2.length) {
		return false;
	}
	for (int i = 0; i < arr1.length; i++) {
		if (arr1[i] != arr2[i]) {
			return false;
		}
	}
	return true;
}

// for test
public static void printArray(int[] arr) {
	if (arr == null) {
		return;
	}
	for (int i = 0; i < arr.length; i++) {
		System.out.print(arr[i] + " ");
	}
	System.out.println();
}

// for test
public static void main(String[] args) {
	int testTime = 500000;
	int maxSize = 100;
	int maxValue = 100;
	boolean succeed = true;
	for (int i = 0; i < testTime; i++) {
		int[] arr1 = generateRandomArray(maxSize, maxValue);
		int[] arr2 = copyArray(arr1);
		selectionSort(arr1);
		comparator(arr2);
		if (!isEqual(arr1, arr2)) {
			succeed = false;
			printArray(arr1);
			printArray(arr2);
			break;
		}
	}
	System.out.println(succeed ? "Nice!" : "***ing ***ed!");

	int[] arr = generateRandomArray(maxSize, maxValue);
	printArray(arr);
	selectionSort(arr);
	printArray(arr);
}

}