package com.heima.array;
import java.util.Arrays;
public class Demo3_Arrays {
/**
* public static String toString(int[] a)
* public static void sort(int[] a)
* public static int binarySearch(int[] a,int key)
*
* public static String toString(int[] a) {
if (a == null) //如果传入的数组是null
return "null"; //返回null
int iMax = a.length - 1; //iMax最大索引
if (iMax == -1) //如果数组中没有元素
return "[]"; //返回[]
StringBuilder b = new StringBuilder(); //线程不安全,效率高
b.append('['); //将[添加到字符串缓冲区中
for (int i = 0; ; i++) { //遍历数组,判断语句没有写默认是true
b.append(a[i]); //把第一个元素添加进字符串缓冲区
if (i == iMax) //如果索引等于了最大索引值
return b.append(']').toString(); //将]添加到字符串缓冲区,在转换成字符串并返回
b.append(", "); //如果不等于最大索引就将, 添加到缓冲区
}
}
private static int binarySearch0(int[] a, int fromIndex, int toIndex,
int key) {
int low = fromIndex; //最小索引0
int high = toIndex - 1; //最大索引数组长度-1
while (low <= high) { //最小索引小于等于最大索引可以循环判断
int mid = (low + high) >>> 1; //求出中间索引值,(最小+最大)/2
int midVal = a[mid]; //通过中间索引获取中间值
if (midVal < key) //中间索引对应的值小于查找的值
low = mid + 1; //最小索引变化
else if (midVal > key) //中间索引对应的值大于查找的值
high = mid - 1; //最大索引变化
else
return mid; // key found //找到了
}
return -(low + 1); // key not found.//-插入点 - 1
}
*/
public static void main(String[] args) {
int[] arr = {33,22,11,44,66,55};
System.out.println(Arrays.toString(arr)); //数组转字符串
Arrays.sort(arr); //排序
System.out.println(Arrays.toString(arr));
int[] arr2 = {11,22,33,44,55,66};
System.out.println(Arrays.binarySearch(arr2, 22));
System.out.println(Arrays.binarySearch(arr2, 66));
System.out.println(Arrays.binarySearch(arr2, 9)); //-插入点-1
}
}
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