JDK源码阅读-------自学笔记(二十六)(java.util.Map 自定义讲解)

一、简介

• Map就是用来存储“键(key)-值(value)”对的.
• 通过键寻找value,所以键不能重复.
• 数组的本质也是一种键值对,区别就是索引一般是数字,而Map的Key可以是任意对象(字符串,数字),相当于把数组的索引范围扩的更大,使用更方便.
• 实际开发中较为常用.

二、Map的常用方法实例

• (1)存储数据(V put(K key, V value))

        Map<Integer,String> map = new HashMap<>(16);

        map.put(1,"a");
        map.put(2,"b");
        map.put(3,"c");
        map.put(4,"d");
        map.put(5,"e");
        map.put(6,"f");
        map.put(7,"g");
        map.put(8,"h");
        map.put(9,"i");

• (2)取出数据(V get(Object key))

        String s = map.get(1);
        System.out.println(s);

• (3)添加对象操作

import java.util.HashMap;
import java.util.Map;

/**
 * @author liuyangos8888
 */
public class MapHasObject {

    public static void main(String[] args) {

        Employee e1 = new Employee(1001, "张三", 50000);
        Employee e2 = new Employee(1002, "李四", 5000);
        Employee e3 = new Employee(1003, "龙五", 6000);
        Employee e4 = new Employee(1001, "五六", 7000);

        Map<Integer, Employee> map = new HashMap<>();

        map.put(1001, e1);
        map.put(1002, e2);
        map.put(1003, e3);
        map.put(1001, e4);

        Employee emp = map.get(1001);

        System.out.println(emp.getEmployeeName());

        System.out.println(map);
    }

}

/**
 * 新建职员对象
 */
class Employee {

    /**
     * 工号
     */
    private int id;

    /**
     * 姓名
     */
    private String employeeName;

    /**
     * 薪资
     */
    private double salary;

    public Employee(int id, String employeeName, double salary) {
        this.id = id;
        this.employeeName = employeeName;
        this.salary = salary;
    }

    public String getEmployeeName() {
        return employeeName;
    }

    public void setEmployeeName(String employeeName) {
        this.employeeName = employeeName;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", employeeName='" + employeeName + '\'' +
                ", salary=" + salary +
                '}';
    }
}

结果: