Java基础 9.22

1.Map接口常用方法

package com.logic.map_;

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

/**
 * @author logic
 * @version 1.0
 */
@SuppressWarnings({"all"})
public class MapMethod {
    public static void main(String[] args) {
        //演示map接口常用方法
        Map map = new HashMap();
        map.put("邓超", new Book("", 100));//OK
        map.put("邓超", "孙俪");//替换-> 一会分析源码
        map.put("王宝强", "马蓉");//OK
        map.put("宋喆", "马蓉");//OK
        map.put("刘令博", null);//OK
        map.put(null, "刘亦菲");//OK
        map.put("鹿晗", "关晓彤");//OK
        map.put("logic", "logic's wife");

        System.out.println("map=" + map);

//        remove:根据键删除映射关系
        map.remove(null);
        System.out.println("map=" + map);
//        get：根据键获取值
        Object val = map.get("鹿晗");
        System.out.println("val=" + val);
//        size:获取元素个数
        System.out.println("k-v=" + map.size());
//        isEmpty:判断个数是否为0
        System.out.println(map.isEmpty());//F
//        clear:清除k-v
        //map.clear();
        System.out.println("map=" + map);
//        containsKey:查找键是否存在
        System.out.println("结果=" + map.containsKey("logic"));//T
    }
}

class Book {
    private String name;
    private int num;

    public Book(String name, int num) {
        this.name = name;
        this.num = num;
    }
}

2.Map接口遍历方法

package com.logic.map_;

import java.util.*;

/**
 * @author logic
 * @version 1.0
 */
@SuppressWarnings({"all"})
public class MapFor {
    public static void main(String[] args) {

        Map map = new HashMap();
        map.put("邓超", "孙俪");
        map.put("王宝强", "马蓉");
        map.put("宋喆", "马蓉");
        map.put("刘令博", null);
        map.put(null, "刘亦菲");
        map.put("鹿晗", "关晓彤");

        //第一组: 先取出 所有的Key , 通过Key 取出对应的Value
        Set keyset = map.keySet();
        //(1) 增强for
        System.out.println("-----第一种方式-------");
        for (Object key : keyset) {
            System.out.println(key + "-" + map.get(key));
        }
        //(2) 迭代器
        System.out.println("----第二种方式--------");
        Iterator iterator = keyset.iterator();
        while (iterator.hasNext()) {
            Object key = iterator.next();
            System.out.println(key + "-" + map.get(key));
        }

        //第二组: 把所有的values取出
        Collection values = map.values();
        //这里可以使用所有的Collections使用的遍历方法
        //(1) 增强for
        System.out.println("---取出所有的value 增强for----");
        for (Object value : values) {
            System.out.println(value);
        }
        //(2) 迭代器
        System.out.println("---取出所有的value 迭代器----");
        Iterator iterator2 = values.iterator();
        while (iterator2.hasNext()) {
            Object value = iterator2.next();
            System.out.println(value);

        }

        //第三组: 通过EntrySet 来获取 k-v
        Set entrySet = map.entrySet();// EntrySet<Map.Entry<K,V>>
        //(1) 增强for
        System.out.println("----使用EntrySet 的 for增强(第3种)----");
        for (Object entry : entrySet) {
            //将entry 转成 Map.Entry
            Map.Entry m = (Map.Entry) entry;
            System.out.println(m.getKey() + "-" + m.getValue());
        }
        //(2) 迭代器
        System.out.println("----使用EntrySet 的 迭代器(第4种)----");
        Iterator iterator3 = entrySet.iterator();
        while (iterator3.hasNext()) {
            Object entry = iterator3.next();
            //System.out.println(next.getClass());//HashMap$Node -实现-> Map.Entry (getKey,getValue)
            //向下转型 Map.Entry
            Map.Entry m = (Map.Entry) entry;
            System.out.println(m.getKey() + "-" + m.getValue());
        }
    }
}

3.Map课堂练习

package com.logic.map_;

import java.util.*;

/**
 * @author logic
 * @version 1.0
 */

/**
 * 使用HashMap添加3个员工对象，要求
 * 键：员工id
 * 值：员工对象
 * <p>
 * 并遍历显示工资>18000的员工(遍历方式最少两种)
 * 员工类：姓名、工资、员工id
 */
@SuppressWarnings({"all"})
public class MapExercise {
    public static void main(String[] args) {
        Map map = new HashMap();
        map.put(01, new Employee("jack", 10000, 01));
        map.put(02, new Employee("logic", 20000, 02));
        map.put(03, new Employee("lucy", 19000, 03));

        System.out.println("===第一种遍历===");
        Set keySet = map.keySet();
        for (Object key : keySet) {
            Employee employee = (Employee) map.get(key);
            if (employee.getSalary() > 18000) {
                System.out.println(employee);
            }
        }

        System.out.println("===第二种遍历===");
        Set set = map.entrySet();
        Iterator iterator = set.iterator();
        while (iterator.hasNext()) {
            Map.Entry next = (Map.Entry) iterator.next();
            Employee employee = (Employee) next.getValue();
            if (employee.getSalary() > 18000) {
                System.out.println(employee);
            }
        }

        System.out.println("===第三种遍历===");
        Collection values = map.values();
        for (Object value : values) {
            Employee employee = (Employee) value;
            if (employee.getSalary() > 18000) {
                System.out.println(employee);
            }
        }
    }
}

class Employee {
    private String name;
    private double salary;
    private int id;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getSalary() {
        return salary;
    }

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

    public int getId() {
        return id;
    }

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

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