容器_TreeMap容器的使用-【官方】百战程序员_IT在线教育培训机构


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public class Users implements Comparable<Users>{
    private String username;
    private int userage;

    public Users(String username, int userage) {
        this.username = username;
        this.userage = userage;
    }

    public Users() {
    }

    @Override
    public boolean equals(Object o) {
        System.out.println("equals...");
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Users users = (Users) o;

        if (userage != users.userage) return false;
        return username != null ? username.equals(users.username) : users.username == null;
    }

    @Override
    public int hashCode() {
        int result = username != null ? username.hashCode() : 0;
        result = 31 * result + userage;
        return result;
    }

    public String getUsername() {
        return username;
    }

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

    public int getUserage() {
        return userage;
    }

    public void setUserage(int userage) {
        this.userage = userage;
    }

    @Override
    public String toString() {
        return "Users{" +
                "username='" + username + '\'' +
                ", userage=" + userage +
                '}';
    }

    //定义比较规则
    //正数：大，负数：小，0：相等
    @Override
    public int compareTo(Users o) {
        if(this.userage < o.getUserage()){
            return 1;
        }
        if(this.userage == o.getUserage()){
           return this.username.compareTo(o.getUsername());
        }
        return -1;
    }
}


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public class TreeMapTest {
    public static void main(String[] args) {
        //实例化TreeMap
        Map<Users,String> map = new TreeMap<>();
        Users u1 = new Users("oldlu",18);
        Users u2 = new Users("admin",22);
        Users u3 = new Users("sxt",22);
        map.put(u1,"oldlu");
        map.put(u2,"admin");
        map.put(u3,"sxt");
        Set<Users> keys = map.keySet();
        for(Users key :keys){
            System.out.println(key+" --------- "+map.get(key));
        }
    }
}

通过比较器实现比较规则


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public class Student {
    private String name;
    private int age;

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

    public Student() {
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

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

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Student student = (Student) o;

        if (age != student.age) return false;
        return name != null ? name.equals(student.name) : student.name == null;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }
}


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public class StudentComparator implements Comparator<Student> {

    //定义比较规则
    @Override
    public int compare(Student o1, Student o2) {
        if(o1.getAge() > o2.getAge()){
            return 1;
        }
        if(o1.getAge() == o2.getAge()){
            return o1.getName().compareTo(o2.getName());
        }
        return -1;
    }
}


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public class TreeMapTest {
    public static void main(String[] args) {
          Map<Student,String> treeMap = new TreeMap<>(new StudentComparator());
    Student s1 = new Student("oldlu",18);
    Student s2 = new Student("admin",22);
    Student s3 = new Student("sxt",22);
    treeMap.put(s1,"oldlu");
    treeMap.put(s2,"admin");
    treeMap.put(s3,"sxt");
    Set<Student> keys1 = treeMap.keySet();
    for(Student key :keys1){
        System.out.println(key+" ---- "+treeMap.get(key));
      }
    }
}

实时效果反馈

1.TreeMap可以对容器中的排序?

A 对Key排序；

B 对Value排序；

C 对Key与Value同时排序；

D 对指定的Key与Value进行排序；

答案

1=>A

容器_HashMap_底层分析_数组扩容容器_TreeMap_底层源码分析

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