学生的姓名长度排序，姓名长度相同时比较学生姓名，姓名相同时，比较学生年龄。

package javaapplication83;
import java.util.*;
import java.util.TreeSet;
import java.util.Comparator;
public class JavaApplication83 {
public static void main(String[] args) {
Student s1=new Student("Tom",18);
Student s2=new Student("Jerry",19);
Student s3=new Student("Jack",18);
Student s4=new Student("Rose",17);
Student s5=new Student("Rose",20);

    Course c1=new Course("C",48);
    Course c2=new Course("JAVA",64);
    Course c3=new Course("C++",48);
    Course c4=new Course("Python",64);
    
    
    Teacher t1=new Teacher("老王",38,"通信技术");
    Teacher t2=new Teacher("老张",52,"通信技术");
    Teacher t3=new Teacher("老李",48,"通信技术");

HashMap map =new HashMap(){
public int compare(Student s1,Student s2){
int num =s1.name.length()-s2.name.length();
int num2=(num==0)?(s1.name.compareTo(s2.name)):num;

    int num3 =((num2==0)?(s1.age-s2.age):num2);
    return num3;  
    }
    };    
    map.put(s1,c1);
    map.put(s2,c2);
    map.put(s3,c3);
    map.put(s4,c4);
    map.put(s5,c4);
    

    Set ks=map.keySet();
    Iterator it =ks.iterator();
    while(it.hasNext()){
        Object key=it.next();
        Object value=map.get(key);
        System.out.println(key+"-->"+value);
    }

package javaapplication83;
public class Course {
public String name;
public int credit;
public Course(){}
public Course(String name, int credit){
super();
this.credit=credit;
this.name=name;
}

public int compareTo(Object o){
       Course c1=(Course)o; 
       if(this.name.charAt(0)==c1.name.charAt(0)){
       return 1;
       }
       else if(this.name.charAt(0)==c1.name.charAt(0)){
               return this.credit-c1.credit;
               }
       else{
           return -1;
       }
   }
public String toString(){
    return this.name+":"+credit+"学分";
}

}

package javaapplication83;
public class Student {
public String name;
public int age;
public Student(){}
public String getName(){
return name;
}
public void setName(){
this.name=name;
}
public int getAge()
{
return age;
}
public void setAge(int age){
this.age=age;
}
public Student(String name, int age){
super();
this.age=age;
this.name=name;
}
public int compare(Object obj){
Student stu=(Student)obj;
if(this.age-stu.age>0){
return 1;
}
if(this.age-stu.age==0){
return this.name.compareTo(stu.name);
}
return -1;
}
public String toString(){
return this.name+":"+age+"岁";
}
}

package javaapplication83;
public class Teacher {
public String name;
public int age;
public String major;
public String getName(){
return name;
}
public void setName(){
this.name=name;
}
public int getAge()
{
return age;
}
public void setAge(int age){
this.age=age;
}
public Teacher(){}
public Teacher(String name, int age,String major){
super();
this.age=age;
this.name=name;
this.major=major;
}
public String toString(){
return this.name+":"+age+":岁"+major;
}
}

你的代码就差一步


package javaapplication83;

import java.util.*;

public class JavaApplication83 {
    public static void main(String[] args) {
        Student s1 = new Student("Tom", 18);
        Student s2 = new Student("Jerry", 19);
        Student s3 = new Student("Jack", 18);
        Student s4 = new Student("Rose", 17);
        Student s5 = new Student("Rose", 20);

        Course c1 = new Course("C", 48);
        Course c2 = new Course("JAVA", 64);
        Course c3 = new Course("C++", 48);
        Course c4 = new Course("Python", 64);

        Teacher t1 = new Teacher("老王", 38, "通信技术");
        Teacher t2 = new Teacher("老张", 52, "通信技术");
        Teacher t3 = new Teacher("老李", 48, "通信技术");

        TreeMap<Student, Course> map = new TreeMap<Student, Course>(new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                int num =s1.name.length()-s2.name.length();
                int num2=(num==0)?(s1.name.compareTo(s2.name)):num;
                int num3 =((num2==0)?(s1.age-s2.age):num2);
                return num3; 
            }
        });
        map.put(s1, c1);
        map.put(s2, c2);
        map.put(s3, c3);
        map.put(s4, c4);
        map.put(s5, c4);

        Set ks = map.keySet();
        Iterator it = ks.iterator();
        while (it.hasNext()) {
            Object key = it.next();
            Object value = map.get(key);
            System.out.println(key + "-->" + value);
        }
    }
}

红色框起来的地方该改成我这样就行了

结果：

整理一下格式吧

关于该问题，我找了一篇非常好的博客，你可以看看是否有帮助，链接：输入学生的个数，姓名，成绩，然后按照学生的成绩的降序来打印学生的姓名

参考代码：

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.*;
import java.util.stream.Collectors;

/**
 * <p>
 * Title Test
 * </p>
 * <p>
 * Description //TODO
 * </p>
 *
 * @Author X
 * @Date 2022-10-17 20:50
 * @Version 1.0
 */
public class Test {

    public static void main(String[] args) {
        List<Student> studentList = new ArrayList<>();
        studentList.add(Student.builder().name("Tom").age(18).build());
        studentList.add(Student.builder().name("Tom").age(16).build());
        studentList.add(Student.builder().name("Jerry").age(19).build());
        studentList.add(Student.builder().name("Jack").age(18).build());
        studentList.add(Student.builder().name("Rose").age(17).build());
        studentList.add(Student.builder().name("Rose").age(20).build());

        //studentList.sort(new NameLengthComparator());
        //studentList.sort(new NameComparator());
        //studentList.sort(new AgeComparator());
        studentList.forEach(System.out::println);


        Map<String, List<Student>> groupMap = studentList.stream()
                .collect(Collectors.groupingBy(Student::getName));

        System.out.println("分组:" + groupMap);

        groupMap.entrySet().stream().sorted((s1, s2) -> {
            try {
                s1.getValue().sort(new AgeComparator());
                s2.getValue().sort(new AgeComparator());
                return s1.getKey().length() - (s2.getKey().length());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return 0;
        }).collect(Collectors.toMap(
                Map.Entry::getKey,
                Map.Entry::getValue,
                (oldVal, newVal) -> oldVal,
                LinkedHashMap::new
        ));
        System.out.println("排序后:" + groupMap);
    }

    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    @Builder
    static class Student {
        String name;
        int age;
    }

    static class NameLengthComparator implements Comparator<Student> {
        @Override
        public int compare(Student s1, Student s2) {
            return s1.getName().length() - (s2.getName().length());
        }
    }

    static class NameComparator implements Comparator<Student> {
        @Override
        public int compare(Student s1, Student s2) {
            return s1.getName().compareTo(s2.getName());
        }
    }

    static class AgeComparator implements Comparator<Student> {
        @Override
        public int compare(Student s1, Student s2) {
            return s1.getAge() - s2.getAge();
        }
    }
}

结果集：

Test.Student(name=Tom, age=18)
Test.Student(name=Tom, age=16)
Test.Student(name=Jerry, age=19)
Test.Student(name=Jack, age=18)
Test.Student(name=Rose, age=17)
Test.Student(name=Rose, age=20)
分组:{Tom=[Test.Student(name=Tom, age=18), Test.Student(name=Tom, age=16)], Rose=[Test.Student(name=Rose, age=17), Test.Student(name=Rose, age=20)], Jack=[Test.Student(name=Jack, age=18)], Jerry=[Test.Student(name=Jerry, age=19)]}
排序后:{Tom=[Test.Student(name=Tom, age=16), Test.Student(name=Tom, age=18)], Rose=[Test.Student(name=Rose, age=17), Test.Student(name=Rose, age=20)], Jack=[Test.Student(name=Jack, age=18)], Jerry=[Test.Student(name=Jerry, age=19)]}

输入学生的个数，姓名，成绩，然后按照学生的成绩的降序来打印学生的姓名_Begin to change的博客-CSDN博客 package seven;import java.util.*;public class seven_17 {public static void main(String[] args) {Scanner input=new Scanner(System.in);System.out.println("Enter input numbers: ");int num...

https://blog.csdn.net/qq_41404557/article/details/88651046