使用Comparator實現集合排序

對任意類型集合對象進行整體排序，排序時將此接口的實現傳遞給Collections.sort方法或者Arrays.sort方法排序.

實現int compare(T o1, T o2);方法，返回正數，零，負數各代表大於，等於，小於。

用於排序的示例代碼如下：

實體類：Student

package com.zjx;

public class Student {

    private String username;

    private int age;

    public Student(String username, int age) {
        this.username = username;
        this.age = age;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

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

用於排序的list集合

  List<Student> students = new ArrayList<Student>() {{
            add(new Student("張三", 12));
            add(new Student("張三", 13));
            add(new Student("張三", 34));
            add(new Student("李四", 54));
            add(new Student("李四", 12));
            add(new Student("王五", 23));
            add(new Student("王五", 21));
        }};

方法一

  //升序
 Collections.sort(students, new Comparator<Student>() {
         @Override
         public int compare(Student o1, Student o2) {
            return o1.getAge() - o2.getAge();
         }
 });
 
 
  //降序
 Collections.sort(students, new Comparator<Student>() {
         @Override
         public int compare(Student o1, Student o2) {
            return o2.getAge() - o1.getAge();
         }
 });

方法二

升序
Collections.sort(students,(o1,o2) ->(o1.getAge()-o2.getAge()));

降序
Collections.sort(students,(o1,o2) ->(o2.getAge()-o1.getAge()));

方法三

Java8實現方式

 Comparator<Student> comparator = Comparator.comparing(Student::getAge);
 
 //升序
 List<Student> list = students.stream().sorted(comparator).collect(Collectors.toList());
 
 //倒序
 List<Student> list = students.stream().sorted(comparator.reversed()).collect(Collectors.toList());