JAVA进阶19

1、冒泡排序

 package cn.zh.abstrac;

 import java.util.Arrays;

 //冒泡排序
 public class Demo019 {
     public static void main(String[] args) {
         int[] values = {22, 11, 33, 2, 4, 5, 66, 55, 44};
         int temp = 0;
         for (int j = 0; j < values.length - 1 - j; j++) {
             boolean flag = true;
             for (int i = 0; i < values.length - 1; i++) {
                 //比较大小，换顺序
                 if (values[i] > values[i + 1]) {
                     temp = values[i];
                     values[i] = values[i + 1];
                     values[i + 1] = temp;

                     flag = false;
                 }
             }
             if (flag) {
                 break;
             }
         }
         System.out.println(Arrays.toString(values));
     }
 }

运行结果图

2、二分法查找法

 package cn.zh.abstrac;

 import java.util.Arrays;

 //二分法查找
 public class TestBinarySearch {
     public static void main(String[] args) {
         int[] arr = {30, 20, 50, 10, 80, 9, 7, 12, 100, 40, 8};
         Arrays.sort(arr);
         System.out.println(Arrays.toString(arr));
         System.out.println(myBinarySearch(arr,40));
     }

     public static int myBinarySearch(int[] arr, int value){
         int low = 0;
         int high = arr.length - 1;

         while (low <= high) {
             int mid = (low + high) / 2;
             if (value == arr[mid]) {
                 return mid;
             }
             if (value > arr[mid]) {
                 low = mid + 1;
             }
             if (value < arr[mid]) {
                 high = mid - 1;
             }
         }
         return -1;
     }
 }

运行结果图

3、可变字符序列与不可变字符序列

注：循环累加用StringBuilder

 package cn.zh.abstrac;

 public class TestStringBuilder {
     public static void main(String[] args) {
         //使用String进行字符串的拼接
         String str1 = "";
         //本质上使用StringBuilder拼接，但是每次循环都会生成一个StringBuilder对象
         long num1 = Runtime.getRuntime().freeMemory(); //获取系统剩余内存空间
         //获取系统的当前时间
         long time1 = System.currentTimeMillis();
         for (int i = 0; i < 5000; i++) {
             //相当于产生了10000个对象
             str1 = str1 + i;
         }
         long num2 = Runtime.getRuntime().freeMemory();
         long time2 = System.currentTimeMillis();
         System.out.println("String占用内存：" + (num1 - num2));
         System.out.println("String占用时间：" + (time2 - time1));

         //使用StringBuilder进行字符串的拼接
         StringBuilder sb1 = new StringBuilder("");
         long num3 = Runtime.getRuntime().freeMemory();
         long time3 = System.currentTimeMillis();
         for (int i = 0; i < 5000; i++) {
             sb1.append(i);
         }
         long num4 = Runtime.getRuntime().freeMemory();
         long time4 = System.currentTimeMillis();
         System.out.println("StringBuilder占用内存：" + (num3 - num4));
         System.out.println("StringBuilder占用时间：" + (time4 - time3));
     }
 }

运行结果图

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