java對集合中某個字段進行排序

下面首先我們先創建一個測試類，這裏重點說一哈，可以實現一個Comparable接口重寫compareTo

public class TestA implements Comparable<TestA> {
    private String name;

    private Integer age;

    public TestA(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "TestA [name=" + name + ", age=" + age + "]";
    }

    @Override
    public int compareTo(TestA o) {
        return this.age.compareTo(o.getAge());
    }
    
}

校驗：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class DemoTest {
    
    public static void main(String[] args) {

        TestA testA1 = new TestA("老張", 3);
        TestA testA2 = new TestA("老李", 1);
        TestA testA3 = new TestA("老王", 2);
        List<TestA> list  = new ArrayList<>();
        list.add(testA1);
        list.add(testA2);
        list.add(testA3);
        System.out.println("排序前--:"+list.toString());
        Collections.sort(list, new Comparator<TestA>() {
            @Override
            public int compare(TestA o1, TestA o2) {
                //升序
                return o1.getAge().compareTo(o2.getAge());
            }
        });
        System.out.println("升序排序後--:"+list.toString());

        Collections.sort(list, new Comparator<TestA>() {
            @Override
            public int compare(TestA o1, TestA o2) {
                //降序
                return o2.getAge().compareTo(o1.getAge());
            }
        });
        System.out.println("降序排序後--:"+list.toString());

    }

}

結果：