Java ArrayList排序
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说明
本文用示例介绍Java的ArrayList排序的方法。
List排序方法
主要有三种方法(按推荐度排序):
- JDK8的stream
- Comparator#compare()
- Comparable#compareTo()
法1:JDK8的stream
法2:Comparator#compare()
需求:用户有成绩和年龄。按成绩排序,若成绩相同,则按年龄排序。
package org.example.a; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; class User{ private int score; private int age; public User(int score, int age){ super(); this.score = score; this.age = age; } public int getScore() { return score; } public void setScore(int score) { this.score = score; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } } public class Demo { public static void main(String[] args) { List<User> users = new ArrayList<User>(); users.add(new User(95, 26)); users.add(new User(84, 23)); users.add(new User(96, 25)); users.add(new User(95, 24)); Collections.sort(users, new Comparator<User>() { @Override public int compare(User o1, User o2) { int i = o2.getScore() - o1.getScore(); if(i == 0){ return o1.getAge() - o2.getAge(); } return i; } }); for(User user : users){ System.out.println(user.getScore() + "," + user.getAge()); } } }
执行结果
96,25
95,24
95,26
84,23
法3:Comparable#compareTo()
默认按增序排序:
package org.example.a; import java.util.ArrayList; import java.util.Collections; import java.util.List; public class Demo { public static void main(String[] args) { List<Integer> nums = new ArrayList<Integer>(); nums.add(3); nums.add(5); nums.add(1); nums.add(0); System.out.println(nums); Collections.sort(nums); System.out.println(nums); } }
执行结果:
[3, 5, 1, 0]
[0, 1, 3, 5]
需求:用户有成绩和年龄。按成绩降序排序,若成绩相同,则按年龄正序排序。
package org.example.a; import java.util.ArrayList; import java.util.Collections; import java.util.List; class User implements Comparable<User>{ private int score; private int age; public User(int score, int age){ super(); this.score = score; this.age = age; } public int getScore() { return score; } public void setScore(int score) { this.score = score; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public int compareTo(User o) { int i = o.getScore() - this.getScore(); if(i == 0){ return this.getAge() - o.getAge(); } return i; } } public class Demo { public static void main(String[] args) { List<User> users = new ArrayList<User>(); users.add(new User(95, 26)); users.add(new User(84, 23)); users.add(new User(96, 25)); users.add(new User(95, 24)); Collections.sort(users); for(User user : users){ System.out.println(user.getScore() + "," + user.getAge()); } } }
执行结果
96,25
95,24
95,26
84,23
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