TreeMap自定义排序（实例）

约定不等于承诺〃 2023-07-04 15:51 23阅读 0赞

TreeMap自定义排序有两种方式：

*  1, 在Student类中实现Comparable，重写compareTo方法
 *  2,在构造函数中new Comparator,匿名内部类，重写compare 方法

以下是第二种具体实现代码逻辑：

package com.example.demo;
    
    import java.util.Comparator;
    import java.util.TreeMap;
    
    /**
     * @Description: Tree Map demo
     * @author: YZD
     * @Date: 2020-02-12 18:53
     * @Version: 1.0
     */
    public class TreeMapDemo {
        /**
         * 需要对 key 和 value 排序时使用
         * 底层使用红黑二叉树
         */
        public static void main(String[] args) {
            // 内部类重写 compare 对 key排序
            TreeMap<Integer, Student> treeMap = new TreeMap<>(new Comparator<Integer>() {
                @Override
                public int compare(Integer o1, Integer o2) {
                    // -1 升序 1 降序
                    if (o1 < o2) {
                        return 1;
                    }
                    if (o1 > o2) {
                        return -1;
                    }
                    return 0;
                }
            });
            Student student = new Student(3, "s");
            Student student2 = new Student(5, "s");
            treeMap.put(3, student);
            treeMap.put(5, student2);
            for (Object o : treeMap.entrySet()) {
                System.out.println(o);
            }
    
            //内部类重写 compare 对 类排序
            TreeMap<Student, String> map = new TreeMap<>(new Comparator<Student>() {
                @Override
                public int compare(Student s1, Student s2) {
                    if (s1.age<s2.age){
                        return 1;
                    }
                    if (s1.age>s2.age){
                        return -1;
                    }
                    return 0;
                }
            });
            map.put(student, "3");
            map.put(student2, "5");
            for (Object o : map.entrySet()) {
                System.out.println(o);
            }
        }
    
        public static class Student {
            //成员变量
            private int age;
            private String name;
    
            public Student(int age, String name) {
                this.age = age;
                this.name = name;
            }
    
            public int getAge() {
                return age;
            }
    
            public void setAge(int age) {
                this.age = age;
            }
    
            public String getName() {
                return name;
            }
    
            public void setName(String name) {
                this.name = name;
            }
    
            @Override
            public String toString() {
                return "Student{" +
                        "age=" + age +
                        ", name='" + name + '\'' +
                        '}';
            }
        }
    }

效果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1Mzg1Njg3_size_16_color_FFFFFF_t_70]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1Mzg1Njg3_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200212201433315.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1Mzg1Njg3,size_16,color_FFFFFF,t_70