Map接口实现类：HashMap

Map接口的实现类HashMap

示例代码：

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

    public Student() {
    }

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

/**
 * HashMap集合的使用
 * 存储结构:哈希表（数组+链表+红黑树）
 * 使用Key的hashcode和equals作为重复依据
 */
public class Demo {
    public static void main(String[] args) {
        //创建集合
        HashMap<Student,String> student = new HashMap<>();
        //1.添加元素
        Student s1 = new Student("a",1);
        Student s2 = new Student("b",2);
        Student s3 = new Student("c",3);
        student.put(s1,"A");
        student.put(s2,"B");
        student.put(s3,"C");
        student.put(new Student("a",1),"E");
        //student.put(s3,"D");
        System.out.println(student.size());
        System.out.println(student.toString());

        //2.删除   根据Key删除
        student.remove(s1);
        System.out.println(student.toString());
        System.out.println(student.size());

        //3.遍历
        //3.1使用KeySet()；
        for (Student key: student.keySet()){
            System.out.println(key+":"+student.get(key));
        }
        //3.2使用entrySet();
        for (Map.Entry<Student,String> entry:student.entrySet()){
            System.out.println(entry.getKey()+":"+entry.getValue());
        }

        //判断
        System.out.println(student.containsKey(new Student("b",2)));
        System.out.println(student.containsValue("A"));
    }
}