JAVA進階19

一、冒泡排序

 1 package cn.zh.abstrac;  2 
 3 import java.util.Arrays;  4 
 5 //冒泡排序
 6 public class Demo019 {  7     public static void main(String[] args) {  8         int[] values = {22, 11, 33, 2, 4, 5, 66, 55, 44};  9         int temp = 0; 10         for (int j = 0; j < values.length - 1 - j; j++) { 11             boolean flag = true; 12             for (int i = 0; i < values.length - 1; i++) { 13                 //比較大小，換順序
14                 if (values[i] > values[i + 1]) { 15                     temp = values[i]; 16                     values[i] = values[i + 1]; 17                     values[i + 1] = temp; 18 
19                     flag = false; 20  } 21  } 22             if (flag) { 23                 break; 24  } 25  } 26  System.out.println(Arrays.toString(values)); 27  } 28 }

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二、二分法查找法

 1 package cn.zh.abstrac;  2 
 3 import java.util.Arrays;  4 
 5 //二分法查找
 6 public class TestBinarySearch {  7     public static void main(String[] args) {  8         int[] arr = {30, 20, 50, 10, 80, 9, 7, 12, 100, 40, 8};  9  Arrays.sort(arr); 10  System.out.println(Arrays.toString(arr)); 11         System.out.println(myBinarySearch(arr,40)); 12  } 13 
14     public static int myBinarySearch(int[] arr, int value){ 15         int low = 0; 16         int high = arr.length - 1; 17 
18         while (low <= high) { 19             int mid = (low + high) / 2; 20             if (value == arr[mid]) { 21                 return mid; 22  } 23             if (value > arr[mid]) { 24                 low = mid + 1; 25  } 26             if (value < arr[mid]) { 27                 high = mid - 1; 28  } 29  } 30         return -1; 31  } 32 }

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運行結果圖

三、可變字符序列與不可變字符序列

注：循環累加用StringBuilder

 1 package cn.zh.abstrac;  2 
 3 public class TestStringBuilder {  4     public static void main(String[] args) {  5         //使用String進行字符串的拼接
 6         String str1 = "";  7         //本質上使用StringBuilder拼接，可是每次循環都會生成一個StringBuilder對象
 8         long num1 = Runtime.getRuntime().freeMemory(); //獲取系統剩餘內存空間  9         //獲取系統的當前時間
10         long time1 = System.currentTimeMillis(); 11         for (int i = 0; i < 5000; i++) { 12             //至關於產生了10000個對象
13             str1 = str1 + i; 14  } 15         long num2 = Runtime.getRuntime().freeMemory(); 16         long time2 = System.currentTimeMillis(); 17         System.out.println("String佔用內存：" + (num1 - num2)); 18         System.out.println("String佔用時間：" + (time2 - time1)); 19 
20         //使用StringBuilder進行字符串的拼接
21         StringBuilder sb1 = new StringBuilder(""); 22         long num3 = Runtime.getRuntime().freeMemory(); 23         long time3 = System.currentTimeMillis(); 24         for (int i = 0; i < 5000; i++) { 25  sb1.append(i); 26  } 27         long num4 = Runtime.getRuntime().freeMemory(); 28         long time4 = System.currentTimeMillis(); 29         System.out.println("StringBuilder佔用內存：" + (num3 - num4)); 30         System.out.println("StringBuilder佔用時間：" + (time4 - time3)); 31  } 32 }

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運行結果圖

四、