Java ArrayList的自定义排序
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Java中实现对list的自定义排序主要通过两种方式
1)让需要进行排序的对象的类实现Comparable接口,重写compareTo(T o)方法,在其中定义排序规则,那么就可以直接调用Collections.sort()来排序对象数组
- public class Student implements Comparable{
- private int id;
- private int age;
- private int height;
- private String name;
-
- public Student(int id, String name, int age, int height) {
- this.id = id;
- this.name = name;
- this.age = age;
- this.height = height;
- }
-
- public int getId() {
- return id;
- }
-
- public int getAge() {
- return age;
- }
-
- public int getHeight() {
- return height;
- }
-
- public String getName() {
- return name;
- }
-
- public void setId(int id) {
- this.id = id;
- }
-
- public void setAge(int age) {
- this.age = age;
- }
-
- public void setName(String name) {
- this.name = name;
- }
-
- public void setHeight(int height) {
- this.height = height;
- }
-
- @Override
- public int compareTo(Object o) {
- Student s = (Student) o;
- if (this.age > s.age) {
- return 1;
- }
- else if (this.age < s.age) {
- return -1;
- }
- else {
- if (this.height >= s.height) {
- return 1;
- }
- else {
- return -1;
- }
- }
- }
- }
测试类:
- import java.util.*;
-
- public class Test {
-
- public static void printData(List<Student> list) {
- for (Student student : list) {
- System.out.println("学号:" + student.getId() + " 姓名:" + student.getName() + " 年龄" + student.getAge() + " 身高:" + student.getHeight());
- }
- }
-
- public static void main(String[] args) {
- List<Student> list = new ArrayList<>();
- list.add(new Student(1, "A", 20, 180));
- list.add(new Student(2, "B", 21, 175));
- list.add(new Student(3, "C", 22, 190));
- list.add(new Student(4, "D", 21, 170));
- list.add(new Student(5, "E", 20, 185));
- System.out.println("before sorted");
- printData(list);
- Collections.sort(list);
- System.out.println("after age and height sorted");
- printData(list);
- }
- }
结果:
- before sorted
- 学号:1 姓名:A 年龄20 身高:180
- 学号:2 姓名:B 年龄21 身高:175
- 学号:3 姓名:C 年龄22 身高:190
- 学号:4 姓名:D 年龄21 身高:170
- 学号:5 姓名:E 年龄20 身高:185
- after age and height sorted
- 学号:1 姓名:A 年龄20 身高:180
- 学号:5 姓名:E 年龄20 身高:185
- 学号:4 姓名:D 年龄21 身高:170
- 学号:2 姓名:B 年龄21 身高:175
- 学号:3 姓名:C 年龄22 身高:190
2)实现比较器接口Comparator,重写compare方法,直接当做参数传进sort中
- public class Student {
- private int id;
- private int age;
- private int height;
- private String name;
-
- public Student(int id, String name, int age, int height) {
- this.id = id;
- this.name = name;
- this.age = age;
- this.height = height;
- }
-
- public int getId() {
- return id;
- }
-
- public int getAge() {
- return age;
- }
-
- public int getHeight() {
- return height;
- }
-
- public String getName() {
- return name;
- }
-
- public void setId(int id) {
- this.id = id;
- }
-
- public void setAge(int age) {
- this.age = age;
- }
-
- public void setName(String name) {
- this.name = name;
- }
-
- public void setHeight(int height) {
- this.height = height;
- }
- }
测试类:
- import java.util.*;
-
- public class Test {
-
- public static void printData(List<Student> list) {
- for (Student student : list) {
- System.out.println("学号:" + student.getId() + " 姓名:" + student.getName() + " 年龄" + student.getAge() + " 身高:" + student.getHeight());
- }
- }
-
- public static void main(String[] args) {
- List<Student> list = new ArrayList<>();
- list.add(new Student(1, "A", 20, 180));
- list.add(new Student(2, "B", 21, 175));
- list.add(new Student(3, "C", 22, 190));
- list.add(new Student(4, "D", 21, 170));
- list.add(new Student(5, "E", 20, 185));
- System.out.println("before sorted");
- printData(list);
- Collections.sort(list, new Comparator<Student>() {
- @Override
- public int compare(Student o1, Student o2) {
- if(o1.getAge() >= o2.getAge()) {
- return 1;
- }
- else {
- return -1;
- }
- }
- });
- System.out.println("after age sorted");
- printData(list);
- Collections.sort(list, new Comparator<Student>() {
- @Override
- public int compare(Student o1, Student o2) {
- if(o1.getAge() > o2.getAge()) {
- return 1;
- }
- else if (o1.getAge() < o2.getAge()){
- return -1;
- }
- else {
- if (o1.getHeight() >= o2.getHeight()) {
- return 1;
- }
- else {
- return -1;
- }
- }
- }
- });
- System.out.println("after age and height sorted");
- printData(list);
- }
- }
输出结果:
- before sorted
- 学号:1 姓名:A 年龄20 身高:180
- 学号:2 姓名:B 年龄21 身高:175
- 学号:3 姓名:C 年龄22 身高:190
- 学号:4 姓名:D 年龄21 身高:170
- 学号:5 姓名:E 年龄20 身高:185
- after age sorted
- 学号:1 姓名:A 年龄20 身高:180
- 学号:5 姓名:E 年龄20 身高:185
- 学号:2 姓名:B 年龄21 身高:175
- 学号:4 姓名:D 年龄21 身高:170
- 学号:3 姓名:C 年龄22 身高:190
- after age and height sorted
- 学号:1 姓名:A 年龄20 身高:180
- 学号:5 姓名:E 年龄20 身高:185
- 学号:4 姓名:D 年龄21 身高:170
- 学号:2 姓名:B 年龄21 身高:175
- 学号:3 姓名:C 年龄22 身高:190
单从上面的例子可以看出排序是稳定的,去看了下java的Collections.sort的源代码,确实是基于稳定的归并排序实现的,内部还做了优化,叫TimSort