Arrays类的用法

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import java.util.Arrays;/* * Arrays:针对数组进行操作的工具类。比如说排序和查找。 * 1:public static String toString(int[] a) 把数组转成字符串 * 2:public static void sort(int[] a) 对数组进行排序 * 3:public static int binarySearch(int[] a,int key) 二分查找 */public class ArraysDemo {public static void main(String[] args) {// 定义一个数组int[] arr = { 24, 69, 80, 57, 13 };// public static String toString(int[] a) 把数组转成字符串System.out.println("排序前：" + Arrays.toString(arr)); //[24, 69, 80, 57, 13]// public static void sort(int[] a) 对数组进行排序Arrays.sort(arr);System.out.println("排序后：" + Arrays.toString(arr));//[13, 24, 57, 69, 80]// [13, 24, 57, 69, 80]// public static int binarySearch(int[] a,int key) 二分查找System.out.println("binarySearch:" + Arrays.binarySearch(arr, 57)); //2System.out.println("binarySearch:" + Arrays.binarySearch(arr, 577)); //-6}}

public static String toString(int[] a)public static void sort(int[] a) 底层是快速排序，知道就可以了。有空看，有问题再问我public static int binarySearch(int[] a,int key)开发原则：只要是对象，我们就要判断该对象是否为null。int[] arr = { 24, 69, 80, 57, 13 };System.out.println("排序前：" + Arrays.toString(arr));public static String toString(int[] a) {//a -- arr -- { 24, 69, 80, 57, 13 }    if (a == null)        return "null"; //说明数组对象不存在    int iMax = a.length - 1; //iMax=4;    if (iMax == -1)        return "[]"; //说明数组存在,但是没有元素。    StringBuilder b = new StringBuilder();    b.append('['); //"["    for (int i = 0; ; i++) {        b.append(a[i]); //"[24, 69, 80, 57, 13"        if (i == iMax)        //"[24, 69, 80, 57, 13]"            return b.append(']').toString();        b.append(", "); //"[24, 69, 80, 57, "    }}-----------------------------------------------------int[] arr = {13, 24, 57, 69, 80};System.out.println("binarySearch:" + Arrays.binarySearch(arr, 577));public static int binarySearch(int[] a, int key) {//a -- arr -- {13, 24, 57, 69, 80}//key -- 577    return binarySearch0(a, 0, a.length, key);}private static int binarySearch0(int[] a, int fromIndex, int toIndex,                                 int key) {    //a -- arr --  {13, 24, 57, 69, 80}    //fromIndex -- 0    //toIndex -- 5    //key -- 577                                                                                                 int low = fromIndex; //low=0    int high = toIndex - 1; //high=4    while (low <= high) {        int mid = (low + high) >>> 1; //mid=2,mid=3,mid=4        int midVal = a[mid]; //midVal=57,midVal=69,midVal=80        if (midVal < key)            low = mid + 1; //low=3,low=4,low=5        else if (midVal > key)            high = mid - 1;        else            return mid; // key found    }    return -(low + 1);  // key not found.}

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