• 初識Arrays類的API：

1     public static void main(String[] args) {
2         int[] arr = {5, 4, 6, 8, 0, 1, 3, 2};
3         System.out.println("陣列地址：" + arr);
4         System.out.println("陣列內容：" + Arrays.toString(arr));
5         Arrays.sort(arr);
6         System.out.println("排序（升序）：" + Arrays.toString(arr));
 
7         System.out.println("二分查詢位置：" + Arrays.binarySearch(arr, 2));
8         System.out.println("二分查詢位置：" + Arrays.binarySearch(arr, 10));
9     }

示例結果：

•  Comparator介面對應的比較器對應用：

 1 public static void main(String[] args) {
 2         //1、使用API完成陣列的升序
 3         int[] ages = {21,22,31,15};
 4         Arrays.sort(ages);
 
 5         System.out.println(Arrays.toString(ages));
 6         System.out.println("-------API只能升序，如何降序？-------");
 7         //自定義排序(只能支援引用型別)：降序
 8         Integer[] ages2 = {12,15,45,30,6};
 9         /**
10          * 引數一 : 被比較的陣列
11          * 引數兒 : 匿名內部欸，代表一個比較器物件
12          */
13         Arrays.sort(ages2, new
 
 Comparator<Integer>() {
14             @Override
15             public int compare(Integer o1, Integer o2) {
16 //                if(o1 > o2){
17 //                    return 1;
18 //                }
19 //                else if(o1 < o2){
20 //                    return -1;
21 //                }
22 //                else {
23 //                    return 0;
24 //                }
25                 //return o1 - o2;
26                 return -(o1 - o2);
27             }
28         });
29         System.out.println(Arrays.toString(ages2));
30 
31         System.out.println("-----------------");
32         Student[] students = new Student[3];
33         students[0] = new Student("張三",21,1.75);
34         students[1] = new Student("李四",19,1.68);
35         students[2] = new Student("王五",20,1.81);
36         System.out.println(Arrays.toString(students));
37 
38         //Arrays.sort(students)  //會程式崩潰
39         Arrays.sort(students, new Comparator<Student>() {
40             @Override
41             public int compare(Student o1, Student o2) {
42                 //return o1.getAge() - o2.getAge(); //按照年齡升序排序
43                 //return o2.getAge() - o1.getAge(); //按照年齡降序排序
44                 //return Double.compare(o1.getHeight(),o2.getHeight()); //按照身高升序
45                 return Double.compare(o2.getHeight(),o1.getHeight()); //按照升高降序
46             }
47         });
48         System.out.println(Arrays.toString(students));
49     }

Student類：

 1 public class Student {
 2     private String name;
 3     private int age;
 4     private double height;
 5 
 6     public String getName() {
 7         return name;
 8     }
 9 
10     public void setName(String name) {
11         this.name = name;
12     }
13 
14     public int getAge() {
15         return age;
16     }
17 
18     public void setAge(int age) {
19         this.age = age;
20     }
21 
22     public double getHeight() {
23         return height;
24     }
25 
26     public void setHeight(double height) {
27         this.height = height;
28     }
29 
30     public Student() {
31     }
32 
33     public Student(String name, int age, double height) {
34         this.name = name;
35         this.age = age;
36         this.height = height;
37     }
38 
39     @Override
40     public String toString() {
41         return "Student{" +
42                 "name='" + name + '\'' +
43                 ", age=" + age +
44                 ", height=" + height +
45                 '}';
46     }
47 }

示例結果：

•  常見演算法（選擇排序、二分查詢）
• 選擇排序：

 1 public static void main(String[] args) {
 2         int[] arr = {1,5,3,2};
 3         for (int i = 0; i < arr.length - 1; i++) { //外層迴圈控制輪數
 4             // i = 0  j: 0, 1, 2, 3
 5             // i = 1  j: 1, 2, 3
 6             // i = 2  j: 2, 3
 7             // i = 3  j: 3
 8             //相鄰兩數選出較小值排在左邊
 9             for (int j = i+1; j < arr.length; j++) {
10                 if(arr[i] > arr[j]){
11                     int tmp = arr[i];
12                     arr[i] = arr[j];
13                     arr[j] = tmp;
14                 }
15             }
16         }
17         System.out.println(Arrays.toString(arr));
18     }

示例結果：

•  二分查詢：

 1 public static void main(String[] args) {
 2         int[] arr = {1,6,51,98,121,150,194,201,205,255};
 3         int key = 201;
 4         //定義左右邊界
 5         int left = 0;
 6         int right = arr.length - 1;
 7         //迴圈條件
 8         while (left <= right){
 9             int midIndex = (left + right) / 2;
10             //中間元素的值大於所要查詢的資料
11             if(arr[midIndex] > key){
12                 right = midIndex - 1;
13             }
14             //中間元素的值小於所要查詢的資料
15             else if(arr[midIndex] < key){
16                 left = midIndex + 1;
17             }
18            //中間元素的值等於所要查詢的資料
19             else{
20                 System.out.println("找到了，索引為：" + midIndex);
21                 break;
22             }
23         }
24         if(left > right){
25             System.out.println("找不到");
26         }
27     }