【数组、ArrayList 、TreeMap的排序方法】自定义类如何排序，存入数组排序、存入ArrayList排序、存入TreeMap排序

1 Integer类，自定义Student类定制比较器comparator排序规则

  //学生类：三个属性
    public static class Student {
        String name;
        int id;
        int age;

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

  //排序Integer类
    //降序
    public static class MyComp implements Comparator<Integer> {
        @Override
        public int compare(Integer o1, Integer o2) {
            return o2 - o1;
        }
    }
   //打印数组
    public static void printArray(Integer[] arr){
        for(Integer i : arr){
            System.out.print(i+",");
        }
        System.out.println();
    }
    //排序Student类
    //根据id从小到大，若id同，按年龄从大到小
    public static class IdShengAgeJiangOrder implements Comparator<Student> {
        @Override
        public int compare(Student o1, Student o2) {
            return o1.id != o2.id ? (o1.id - o2.id) : (o2.age - o1.age);
        }
    }
    
    //排序Student类
    //id升序
    public static class IdAscending implements Comparator<Student> {
        @Override
        public int compare(Student o1, Student o2) {
            return o1.id - o2.id;
        }
    }
    
    //排序Student类
    //id降序
    public static class IdDescending implements Comparator<Student> {
        @Override
        public int compare(Student o1, Student o2) {
            return o2.id - o1.id;
        }
    }

    //打印学生三个属性
    public static void printStudents(Student[] students){
        for(Student s : students){
            System.out.println("Name:"+s.name+" Id:"+s.id+" Age:"+s.age);
        }
    }

2 数组[]排序Array.sort

  public static void main(String[] args) {
        //Integer数组用MyComp排序并打印
        Integer[] arr = { 1, 2, 3, 5, 2, 1 };
        Arrays.sort(arr, new MyComp());
        printArray(arr);
   		System.out.println("第一条打印");
        Student[] stus = {stu1, stu2, stu3, stu4, stu5};
        Arrays.sort(stus, new IdShengAgeJiangOrder());
        printStudents(stus);
}

结果：

5,3,2,2,1,1,
第一条打印
Name:E Id:3 Age:25
Name:D Id:3 Age:4
Name:B Id:4 Age:20
Name:A Id:4 Age:18
Name:C Id:4 Age:8

3 ArrayList排序，两种调用排序的方法 1、list.sort(比较器); 2、Collections.sort(list, 比较器);

  

    public static void main(String[] args) {

        Student stu1 = new Student("A",4,18);
        Student stu2 = new Student("B",4,20);
        Student stu3 = new Student("C",4,8);
        Student stu4 = new Student("D",3, 4);
        Student stu5 = new Student("E",3, 25);
        //---------------------------------------------------------------
     
        System.out.println("第二条打印");
        ArrayList<Student> stus2 = new ArrayList<>();
        stus2.add(stu1);
        stus2.add(stu2);
        stus2.add(stu3);
        stus2.add(stu4);
        stus2.add(stu5);
        
        //5个Student的ArrayList用.sort(比较器）排序
        /**ArrayList两种调用排序写法-------------------------------------------------*/
        //ArrayList，两种排序都可以，本身是按照添加顺序存储
        stus2.sort(new IdShengAgeJiangOrder());
        //♥ Collections.sort(stus2, new IdShengAgeJiangOrder());
        for(int i = 0; i < stus2.size(); i++){
            Student s = stus2.get(i);
            System.out.println(s.name+","+s.id+","+s.age);
        }

       


    }
}

运行结果：

第二条打印
E,3,25
D,3,4
B,4,20
A,4,18
C,4,8

4 TreeMap排序，三种new时有排序的方法1、new TreeMap参数用lambda表达式代替比较器2、TreeMap参数new含比较器的类对象3、 TreeMap参数new含比较器的匿名类对象(new Comparator (){实现compare方法})；

 System.out.println("第三条打印");
        stu1 = new Student("A", 4, 40);
        stu2 = new Student("B", 4, 18);
        stu3 = new Student("C", 4, 34);
        stu4 = new Student("D", 4, 89);
        stu5 = new Student("E", 4, 5);


        /**TreeMap的3种排序写法---------------------------------------------------------*/
        //5个Student的TreeMap用new时，new时用lambda表达式作为比较器((a,b) -> (a.id - b.id)
        //缺点，若id相同则只能存储一个，不能再根据age排序
        //♥TreeMap stus3 = new TreeMap<>((a,b) -> (a.id - b.id));

        //5个Student的数组，用IdSheng……排序，打印
        //♥TreeMap stus3 = new TreeMap<>(new IdShengAgeJiangOrder());

        //直接在参数部分实现匿名类重写比较器
        TreeMap<Student, String> stus3 = new TreeMap<>(new Comparator<Student> (){
            @Override
            public int compare(Student o1, Student o2) {
                return o1.id != o1.id ? o1.id - o2.id : o1.age - o2.age;
            }
        });
        stus3.put(stu1, "我是学生1,我的名字叫A");
        stus3.put(stu2, "我是学生2,我的名字叫B");
        stus3.put(stu3, "我是学生3,我的名字叫C");
        stus3.put(stu4, "我是学生4,我的名字叫D");
        stus3.put(stu5, "我是学生5,我的名字叫E");
        for(Student s : stus3.keySet()){
            System.out.println(s.name+","+s.id+","+s.age);
        }

运行结果：

第三条打印
E,4,5
B,4,18
C,4,34
A,4,40
D,4,89