Java中實現對list的自定義排序主要通過兩種方式
1)讓需要進行排序的對象的類實現Comparable接口,重寫compareTo(T o)方法,在其中定義排序規則,那麼就可以直接調用Collections.sort()來排序對象數組
- 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;
- }
- }
- }
- }
測試類:
- import java.util.*;
- public class Test {
- public static void printData(List<Student> list) {
- for (Student student : list) {
- System.out.println("學號:" + student.getId() + " 姓名:" + student.getName() + " 年齡" + 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);
- }
- }
結果:
- before sorted
- 學號:1 姓名:A 年齡20 身高:180
- 學號:2 姓名:B 年齡21 身高:175
- 學號:3 姓名:C 年齡22 身高:190
- 學號:4 姓名:D 年齡21 身高:170
- 學號:5 姓名:E 年齡20 身高:185
- after age and height sorted
- 學號:1 姓名:A 年齡20 身高:180
- 學號:5 姓名:E 年齡20 身高:185
- 學號:4 姓名:D 年齡21 身高:170
- 學號:2 姓名:B 年齡21 身高:175
- 學號:3 姓名:C 年齡22 身高:190
2)實現比較器接口Comparator,重寫compare方法,直接當做參數傳進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;
- }
- }
測試類:
- import java.util.*;
- public class Test {
- public static void printData(List<Student> list) {
- for (Student student : list) {
- System.out.println("學號:" + student.getId() + " 姓名:" + student.getName() + " 年齡" + 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);
- }
- }
輸出結果:
- before sorted
- 學號:1 姓名:A 年齡20 身高:180
- 學號:2 姓名:B 年齡21 身高:175
- 學號:3 姓名:C 年齡22 身高:190
- 學號:4 姓名:D 年齡21 身高:170
- 學號:5 姓名:E 年齡20 身高:185
- after age sorted
- 學號:1 姓名:A 年齡20 身高:180
- 學號:5 姓名:E 年齡20 身高:185
- 學號:2 姓名:B 年齡21 身高:175
- 學號:4 姓名:D 年齡21 身高:170
- 學號:3 姓名:C 年齡22 身高:190
- after age and height sorted
- 學號:1 姓名:A 年齡20 身高:180
- 學號:5 姓名:E 年齡20 身高:185
- 學號:4 姓名:D 年齡21 身高:170
- 學號:2 姓名:B 年齡21 身高:175
- 學號:3 姓名:C 年齡22 身高:190
單從上面的例子可以看出排序是穩定的,去看了下java的Collections.sort的源代碼,確實是基於穩定的歸併排序實現的,內部還做了優化,叫TimSort