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

4、