Set_advanced_project/Map_module/src/HashMap_package1/HashMap_demo.java

package HashMap_package1;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.function.BiConsumer;

public class HashMap_demo {
    public static void main(String[] args) {
        /*
        需求：创建一个HashMap集合，键是学生对象(Student)，值是籍贯(String)。
        存储三个键值对元素，并遍历
        要求：同姓名，同年龄认为是同一个学生

        核心点：
            HashMap的键位置如果存储的是自定义对象，需要重写hashCode和equals方法。
         */

        //1、创建HashMap的对象
        HashMap<Student, String> hm = new HashMap<>();

        //2、创建三个学生对象
        Student s1 = new Student("zhangsan", 23);
        Student s2 = new Student("lisi", 24);
        Student s3 = new Student("wangwu", 25);

        //3、添加元素
        hm.put(s1, "江苏");
        hm.put(s2, "浙江");
        hm.put(s3, "福建");

        //4、遍历集合
        Set<Student> keys = hm.keySet();
        for (Student key : keys) {
            String value = hm.get(key);
            System.out.println(key + "=" + value);
        }

        System.out.println("----------------------------------------");

        Set<Map.Entry<Student, String>> entries = hm.entrySet();
        for (Map.Entry<Student, String> entry : entries) {
            Student key = entry.getKey();
            String value = entry.getValue();

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

        System.out.println("----------------------------------------");

        hm.forEach(new BiConsumer<Student, String>() {
            @Override
            public void accept(Student key, String value) {
                System.out.println(key + "=" + value);
            }
        });
    }
}