通俗来说就是自定义比较
- 比较器的实质就是重载比较运算符(在C++中叫重载比较运算符)
- 比较器可以很好的应用在特殊标准的排序上
- 比较器可以很好的应用在根据特殊标准排序的结构上
基本使用:
对于任意比较器,首先指定两个对象，o1，o2，
返回值有统一的规范：
当返回负数时：认为o1应该排在o2的前面；
当返回负数时：认为o2应该排在o1的前面；
当返回0时:认为谁排前面都行；
核心代码
public static class Student {
public String name;
public int id;
public int age;
public Student(String name, int id, int age) {
this.name = name;
this.id = id;
this.age = age;
}
}
public static class IdAscendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.id - o2.id;
}
}
public static class IdDescendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o2.id - o1.id;
}
}
public static class AgeAscendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.age - o2.age;
}
}
public static class AgeDescendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o2.age - o1.age;
}
}
public static void printStudents(Student[] students) {
for (Student student : students) {
System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
}
}
public static void printArray(Integer[] arr) {
if (arr == null) {
return;
}
for (int i = 0; i < arr.length; i++) {
System.out.print(arr[i] + " ");
}
System.out.println();
}
public static class MyComp implements Comparator<Integer> {
@Override
public int compare(Integer o1, Integer o2) {
return o2 - o1;
}
}
全部代码
package class03;
import java.util.Arrays;
import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.TreeSet;
public class Code03_Comparator {
public static class Student {
public String name;
public int id;
public int age;
public Student(String name, int id, int age) {
this.name = name;
this.id = id;
this.age = age;
}
}
public static class IdAscendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.id - o2.id;
}
}
public static class IdDescendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o2.id - o1.id;
}
}
public static class AgeAscendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.age - o2.age;
}
}
public static class AgeDescendingComparator implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o2.age - o1.age;
}
}
public static void printStudents(Student[] students) {
for (Student student : students) {
System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
}
}
public static void printArray(Integer[] arr) {
if (arr == null) {
return;
}
for (int i = 0; i < arr.length; i++) {
System.out.print(arr[i] + " ");
}
System.out.println();
}
public static class MyComp implements Comparator<Integer> {
@Override
public int compare(Integer o1, Integer o2) {
return o2 - o1;
}
}
public static void main(String[] args) {
Student student1 = new Student("A", 2, 23);
Student student2 = new Student("B", 3, 21);
Student student3 = new Student("C", 1, 22);
Student[] students = new Student[] { student1, student2, student3 };
Arrays.sort(students, new IdAscendingComparator());
printStudents(students);
System.out.println("===========================");
Arrays.sort(students, new IdDescendingComparator());
printStudents(students);
System.out.println("===========================");
Arrays.sort(students, new AgeAscendingComparator());
printStudents(students);
System.out.println("===========================");
Arrays.sort(students, new AgeDescendingComparator());
printStudents(students);
System.out.println("===========================");
System.out.println("===========================");
System.out.println("===========================");
System.out.println("===========================");
PriorityQueue<Student> maxHeapBasedAge = new PriorityQueue<>(new AgeDescendingComparator());
maxHeapBasedAge.add(student1);
maxHeapBasedAge.add(student2);
maxHeapBasedAge.add(student3);
while (!maxHeapBasedAge.isEmpty()) {
Student student = maxHeapBasedAge.poll();
System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
}
System.out.println("===========================");
PriorityQueue<Student> minHeapBasedId = new PriorityQueue<>(new IdAscendingComparator());
minHeapBasedId.add(student1);
minHeapBasedId.add(student2);
minHeapBasedId.add(student3);
while (!minHeapBasedId.isEmpty()) {
Student student = minHeapBasedId.poll();
System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
}
System.out.println("===========================");
System.out.println("===========================");
System.out.println("===========================");
TreeSet<Student> treeAgeDescending = new TreeSet<>(new AgeDescendingComparator());
treeAgeDescending.add(student1);
treeAgeDescending.add(student2);
treeAgeDescending.add(student3);
Student studentFirst = treeAgeDescending.first();
System.out.println("Name : " + studentFirst.name + ", Id : " + studentFirst.id + ", Age : " + studentFirst.age);
Student studentLast = treeAgeDescending.last();
System.out.println("Name : " + studentLast.name + ", Id : " + studentLast.id + ", Age : " + studentLast.age);
System.out.println("===========================");
}
}