HashMap的使用

package com.ding.mymap;


import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class MapDemo1 {

    public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>();

        map.put("张无忌", "赵敏");
        map.put("杨过", "小龙女");
        map.put("郭靖", "芙蓉");

        Set<String> strings = map.keySet();//获取所有值的集合
        for (String string : strings) {
            System.out.println(string);
        }

        Collection<String> values = map.values();//获取所有值的集合
        for (String value : values) {
            System.out.println(value);
        }

        Set<Map.Entry<String, String>> entrySet = map.entrySet();//获取所有键值对对象的集合
        for (Map.Entry<String, String> entry : entrySet) {
            String key = entry.getKey();
            String value = entry.getValue();

            System.out.println(key+"---->"+value);
        }

    }



}

案例需求

• 创建一个HashMap集合，键是学生对象(Student)，值是居住地 (String)。存储多个元素，并遍历。
• 要求保证键的唯一性：如果学生对象的成员变量值相同，我们就认为是同一个对象

package com.ding.mymap;


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 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;
    }

}

package com.ding.mymap;


import java.util.HashMap;
import java.util.Set;

public class HashMapDemo1 {

    public static void main(String[] args) {
        HashMap<Student, String> hm = new HashMap<Student, String>();

        Student s1 = new Student("小明", 23);
        Student s2 = new Student("小红", 23);
        Student s3 = new Student("小刚", 22);
        Student s4 = new Student("小其", 24);
        Student s5 = new Student("小其", 24);


        //把学生添加到集合
        hm.put(s1, "西安");
        hm.put(s2, "武汉");
        hm.put(s3, "郑州");
        hm.put(s4, "北京");
        hm.put(s5, "北京");

        Set<Student> students = hm.keySet();
        for (Student student : students) {
            String value = hm.get(student);
            System.out.println(student.getName()+"---->"+student.getAge()+"---->"+value);

           /*
            小其---->24---->北京
            小刚---->22---->郑州
            小红---->23---->武汉
            小明---->23---->西安
            */
        }
    }

}