1 import java.util.Arrays; //通过API查找，并不属于long包，所以需要导包 2 public class ArraysDemo { 3 public static void main(String[] args) { 4 // 定义一个数组 5 int[] arr = { 24, 69, 80, 57, 13 }; 6  7 // public static String toString(int[] a) 把数组转成字符串 8 System.out.println("排序前：" + Arrays.toString(arr)); 9 10 // public static void sort(int[] a) 对数组进行排序11 Arrays.sort(arr);12 System.out.println("排序后：" + Arrays.toString(arr));13 14 // [13, 24, 57, 69, 80] 为了演示二分查找方法的效果才先对数组进行排序，正常来说不能这样。15 // public static int binarySearch(int[] a,int key) 二分查找16 System.out.println("binarySearch:" + Arrays.binarySearch(arr, 57));17 System.out.println("binarySearch:" + Arrays.binarySearch(arr, 577));18 }19 }

 1 int[] arr = { 24, 69, 80, 57, 13 }; 2 System.out.println("排序前：" + Arrays.toString(arr)); 3  4 toString的源码： 5 public static String toString(int[] a) { 6 //a -- arr -- { 24, 69, 80, 57, 13 } 7  8 if (a == null) 9 return "null"; //说明数组对象不存在10 int iMax = a.length - 1; //iMax=4;11 if (iMax == -1)12 return "[]"; //说明数组存在,但是没有元素。13 14 StringBuilder b = new StringBuilder();15 b.append(‘[‘); //"["16 for (int i = 0; ; i++) { //中间为空，则默认为true，永远进行17 b.append(a[i]); //"[24, 69, 80, 57, 13"18 if (i == iMax) //限制了循环次数19 //"[24, 69, 80, 57, 13]"20 return b.append(‘]‘).toString();21 b.append(", "); //"[24, 69, 80, 57, "22 }23 }24 -----------------------------------------------------25 写的代码：26 int[] arr = {13, 24, 57, 69, 80};27 System.out.println("binarySearch:" + Arrays.binarySearch(arr, 577));28 29 binarySearch的源码：30 public static int binarySearch(int[] a, int key) {31 //a -- arr -- {13, 24, 57, 69, 80}32 //key -- 57733 return binarySearch0(a, 0, a.length, key);34 }35 36 private static int binarySearch0(int[] a, int fromIndex, int toIndex,37 int key) {38 //a -- arr -- {13, 24, 57, 69, 80}39 //fromIndex -- 040 //toIndex -- 541 //key -- 577 42 43 44 int low = fromIndex; //最小索引low=045 int high = toIndex - 1; //最大索引high=446 47 while (low <= high) {48 //无符号右移，相当于(low+hith)/249 int mid = (low + high) >>> 1; //mid=2,mid=3,mid=450 int midVal = a[mid]; //midVal=57,midVal=69,midVal=8051 52 if (midVal < key)53 low = mid + 1; //low=3,low=4,low=554 else if (midVal > key)55 high = mid - 1;56 else57 return mid; // key found58 }59 return -(low + 1); // key not found.60 }