s-day03--Collections里面的sort方法以及Comparable接口

s-day03/src/com/inmind/colletions04/Demo13.java

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+package com.inmind.colletions04;
+
+import java.util.ArrayList;
+import java.util.Collections;
+/*
+    7.Collections里面的sort方法以及Comparable接口
+    public static <T> void sort(List<T> list):将集合中元素按照默认规则排序。
+
+    注意:
+        1.要使用以上的排序api,那么List集合的泛型的类型必须实现Comparable接口.
+        2.当一个类实现了Comparable接口就表示该类具有了自然排序功能
+
+ */
+public class Demo13 {
+    public static void main(String[] args) {
+        ArrayList<Student> students = new ArrayList<>();
+        Collections.addAll(students
+                , new Student("张三1", 19)
+                , new Student("张三2", 20)
+                , new Student("张三3", 18)
+                , new Student("张三4", 21)
+        );
+        System.out.println(students);
+        //希望集合的学生按年龄排序（升序，降序）
+        Collections.sort(students);
+        System.out.println(students);
+    }
+}

s-day03/src/com/inmind/colletions04/Student.java

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+package com.inmind.colletions04;
+
+import java.util.Objects;
+
+public class Student implements Comparable<Student> {
+    String name;
+    int age;
+
+    public Student(String name, int age) {
+        this.name = name;
+        this.age = age;
+    }
+
+    @Override
+    public String toString() {
+        return "Student{" +
+                "name='" + name + '\'' +
+                ", age=" + age +
+                '}';
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) return false;
+
+        Student student = (Student) o;
+        return age == student.age && Objects.equals(name, student.name);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = Objects.hashCode(name);
+        result = 31 * result + age;
+        return result;
+    }
+
+    /*
+    排序功能方法
+    我-它：升序
+    它-我：降序
+     */
+    @Override
+    public int compareTo(Student s) {
+//        return this.age-s.age;//升序
+        return s.age-this.age;//降序
+    }
+}