比较器

  1. // 任何比较器：
  2. // compare方法里，遵循一个统一的规范：
  3. // 返回负数的时候，认为第一个参数应该排在前面
  4. // 返回正数的时候，认为第二个参数应该排在前面
  5. // 返回0的时候，认为无所谓谁放前面
  6. public static class IdShengAgeJiangOrder implements Comparator<Student> {
  8.     // 根据id从小到大，但是如果id一样，按照年龄从大到小
  9.     @Override
  10.     public int compare(Student o1, Student o2) {
  11.         return o1.id != o2.id ? (o1.id - o2.id) : (o2.age - o1.age);
  12.     }
  14. }
  16. public static class IdAscendingComparator implements Comparator<Student> {
  18.     // 返回负数的时候，第一个参数排在前面
  19.     // 返回正数的时候，第二个参数排在前面
  20.     // 返回0的时候，谁在前面无所谓
  21.     @Override
  22.     public int compare(Student o1, Student o2) {
  23.         return o1.id - o2.id;
  24.     }
  26. }
  28. public static class IdDescendingComparator implements Comparator<Student> {
  30.     @Override
  31.     public int compare(Student o1, Student o2) {
  32.         return o2.id - o1.id;
  33.     }
  35. }
  37. // 先按照id排序，id小的，放前面；
  38. // id一样，age大的，前面；
  39. public static class IdInAgeDe implements Comparator<Student> {
  41.     @Override
  42.     public int compare(Student o1, Student o2) {
  43.         return o1.id != o2.id ? o1.id - o2.id : (o2.age - o1.age);
  44.     }
  46. }
  48. public static void printStudents(Student[] students) {
  49.     for (Student student : students) {
  50.         System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
  51.     }
  52. }
  54. public static void printArray(Integer[] arr) {
  55.     if (arr == null) {
  56.         return;
  57.     }
  58.     for (int i = 0; i < arr.length; i++) {
  59.         System.out.print(arr[i] + " ");
  60.     }
  61.     System.out.println();
  62. }
  64. public static class MyComp implements Comparator<Integer> {
  66.     @Override
  67.     public int compare(Integer o1, Integer o2) {
  68.         return o2 - o1;
  69.     }
  71. }
  73. public static class AComp implements Comparator<Integer> {
  75.     // 如果返回负数，认为第一个参数应该拍在前面
  76.     // 如果返回正数，认为第二个参数应该拍在前面
  77.     // 如果返回0，认为谁放前面都行
  78.     @Override
  79.     public int compare(Integer arg0, Integer arg1) {
  81.         return arg1 - arg0;
  83.         //            return 0;
  84.     }
  86. }
  88. public static void main(String[] args) {
  90.     Integer[] arr = { 5, 4, 3, 2, 7, 9, 1, 0 };
  92.     Arrays.sort(arr, new AComp());
  94.     for (int i = 0; i < arr.length; i++) {
  95.         System.out.println(arr[i]);
  96.     }
  98.     System.out.println("===========================");
  100.     Student student1 = new Student("A", 4, 40);
  101.     Student student2 = new Student("B", 4, 21);
  102.     Student student3 = new Student("C", 3, 12);
  103.     Student student4 = new Student("D", 3, 62);
  104.     Student student5 = new Student("E", 3, 42);
  105.     // D E C A B
  107.     Student[] students = new Student[] { student1, student2, student3, student4, student5 };
  108.     System.out.println("第一条打印");
  110.     Arrays.sort(students, new IdShengAgeJiangOrder());
  111.     for (int i = 0; i < students.length; i++) {
  112.         Student s = students[i];
  113.         System.out.println(s.name + "," + s.id + "," + s.age);
  114.     }
  116.     System.out.println("第二条打印");
  117.     ArrayList<Student> studentList = new ArrayList<>();
  118.     studentList.add(student1);
  119.     studentList.add(student2);
  120.     studentList.add(student3);
  121.     studentList.add(student4);
  122.     studentList.add(student5);
  123.     studentList.sort(new IdShengAgeJiangOrder());
  124.     for (int i = 0; i < studentList.size(); i++) {
  125.         Student s = studentList.get(i);
  126.         System.out.println(s.name + "," + s.id + "," + s.age);
  127.     }
  128.     // N * logN
  129.     System.out.println("第三条打印");
  130.     student1 = new Student("A", 4, 40);
  131.     student2 = new Student("B", 4, 21);
  132.     student3 = new Student("C", 4, 12);
  133.     student4 = new Student("D", 4, 62);
  134.     student5 = new Student("E", 4, 42);
  135.     TreeMap<Student, String> treeMap = new TreeMap<>((a, b) -> (a.id - b.id));
  136.     treeMap.put(student1, "我是学生1，我的名字叫A");
  137.     treeMap.put(student2, "我是学生2，我的名字叫B");
  138.     treeMap.put(student3, "我是学生3，我的名字叫C");
  139.     treeMap.put(student4, "我是学生4，我的名字叫D");
  140.     treeMap.put(student5, "我是学生5，我的名字叫E");
  141.     for (Student s : treeMap.keySet()) {
  142.         System.out.println(s.name + "," + s.id + "," + s.age);
  143.     }
  145. }