MAP

MAP接口的常用方法

import java.util.HashMap;
import java.util.Map;
public class HashMap01 {
    public static void main(String[] args) {
       Map map=new HashMap();
       map.put("cai","y");
       map.put("chun","a");
       map.put("mei","n");
       map.put("cai","cai");
        System.out.println(map);//{chun=a, mei=n, cai=cai}
    map.remove("cai");
        System.out.println(map);
        System.out.println(map.get("mei"));//n
    }
}

MAP的遍历

• 通过keySet集合遍历key 查找value
• 直接通过values集合 遍历输出value
• 通过entry集合里面的 Map.Entry (k,v)输出数据，注意Map.Entry和entry的转型

import arraylist.Iterator01;
import javax.swing.text.html.HTMLDocument;
import java.util.*;
public class HashMap02 {
    public static void main(String[] args) {
        Map map= new HashMap();
        map.put("cai","蔡");
        map.put("chun","春");
        map.put("mei","梅");
    //这是在keyset 集合里面通过遍历key 然后取出value
        Set set=map.keySet();
        for (Object key:set) {
            System.out.println(key+ "-" + map.get(key));
        }
    //用迭代器一定要调用！！
        Iterator iterator= set.iterator();
        while (iterator.hasNext()){
            Object key=iterator.next();
            System.out.println(key +"-" +map.get(key));
        }
    //通过遍历 values集合 ，获取value的值
        Collection values = map.values();
        for (Object value:values) {
            System.out.println(value);
        }
    //迭代器要引用
        Iterator iterator1= values.iterator();
        while (iterator1.hasNext()){
            Object value=iterator1.next();
            System.out.println(value);
        }
    //通过entry这个集合 来查找Map.Entry里面的（k,v）
        Set entrySet = map.entrySet();
        for (Object entry :entrySet) {
          Map.Entry m=(Map.Entry)entry;//向下转型，entry（object）
            System.out.println(m.getKey() +"-"+ m.getValue());
        }
        Iterator iterator2 = entrySet.iterator();
        while (iterator2.hasNext()){
            Map.Entry m=(Map.Entry)iterator2.next();//向下转型，iterator(objec)
            System.out.println(m.getKey() +"-"+m.getValue());
        }
    }
}

import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;
import java.security.KeyStore;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapexer01 {
    public static void main(String[] args) {
        Map map = new HashMap();
        map.put(1,new Person(1,"cai",12000));
        map.put(2,new Person(2,"cai1",1200));
        map.put(3,new Person(3,"cai2",12001));
        Set keySet = map.keySet();
        //用增强for循环
        for (Object key :keySet) {
            Person person=(Person) map.get(key);
            if (person.getSal()>1880){
                System.out.println(person);
            }
        }
        //用entrySet迭代器
        Set entrySet = map.entrySet();
        Iterator iterator = entrySet.iterator();
        while (iterator.hasNext()){
            Map.Entry entry=(Map.Entry)iterator.next();
            Person person=(Person) entry.getValue();
            if (person.getSal()>10000){
                System.out.println(person);
            }
        }
    }
    }
class Person{
    private int id;
    private String name;
    private int sal;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getSal() {
        return sal;
    }
    public void setSal(int sal) {
        this.sal = sal;
    }
    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", sal=" + sal +
                '}';
    }
    public Person(int id, String name, int sal) {
        this.id = id;
        this.name = name;
        this.sal = sal;
    }
}