java基础之LinkedHashMap类

目录

一：概念

二：例子

1：key与value是Integer和String

2：key是Integer，value 是Student

3：key是Student，value 是Integer

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一：概念

是实现了Map接口，底层是依赖于哈希表和链表的，具有可预知的遍历顺序

哈希表保证唯一性，保证的是Key的唯一性

链表保证有序，保证的是键的有序（存储和取出顺序一致）

（再次输入一样的key然后输入vaule时会更新值）

注意：LinkedHashMap类继承于HashMap而HashMap继承于Map所以重写了他们具有的方法

二：例子

1：key与value是Integer和String

package protice5;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

public class Test5 {
    public static void main(String[] args) {
        //创建对象指定泛型
        LinkedHashMap<Integer, String> i = new LinkedHashMap<Integer, String>();
        //添加元素
        i.put(1, "hello");
        i.put(2, "world");
        i.put(3,  "java");
        i.put(4, "hadoop");
        //遍历得到key和value并输出
        Set<Map.Entry<Integer, String>> entries = i.entrySet();
        for (Map.Entry<Integer, String> entry : entries) {
            System.out.println(entry.getKey()+"**"+entry.getValue());
        }

    }
}

2：key是Integer，value 是Student

package protice5;

import java.util.Objects;

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

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

    public Student() {
    }

    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 String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", 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;
        return age == student.age &&
                Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {

        return Objects.hash(name, age);
    }
}

package protice5;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

public class Test6 {
    public static void main(String[] args) {
        //创建LinkedHashMap对象并指定泛型
        LinkedHashMap<Integer, Student> i = new LinkedHashMap<Integer, Student>();
        //创建学生对象
        Student s1 = new Student("小花", 19);
        Student s2 = new Student("小花", 19);
        Student s3 = new Student("小李", 20);
        Student s4 = new Student("小可", 17);
        //向map中添加元素
        i.put( 2,s1);
        i.put( 7,s2);
        i.put( 6,s3);
        i.put( 1 ,s4);
        //遍历得到key和value
        Set<Map.Entry<Integer, Student>> entries = i.entrySet();
        for (Map.Entry<Integer, Student> entry : entries) {
            System.out.println(entry.getKey()+"**"+entry.getValue());
        }
    }
}

3：key是Student，value 是Integer

package protice5;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

public class Test4 {
    public static void main(String[] args) {
        LinkedHashMap<Student, String> s = new LinkedHashMap<Student, String>();
        Student s1 = new Student("小花", 19);
        Student s2 = new Student("小花", 19);
        Student s3 = new Student("小李", 20);
        Student s4 = new Student("小可", 17);
        s.put( s1,"001");
        s.put( s2,"002");
        s.put( s3,"003");
        s.put( s4,"004");
        Set<Map.Entry<Student, String>> entries = s.entrySet();
        for (Map.Entry<Student, String> entry : entries) {
            System.out.println(entry.getKey()+"**"+entry.getValue());
        }

    }
}