Java集合之Map接口与实现类详解

V put(K key, V value)	//向Map集合中添加键值对 

V get(Object key)			//返回指定键映射到的值，通过key获取value 

void clear()		//从此映射中删除所有映射,清空Map集合

boolean containsKey(Object key)	//判断Map是否包含某个key

boolean containsValue(Object value)	//判断Map是否包含某个value

boolean isEmpty()	//判断Map中元素个数是否为0

Set<K> keySet()	//获取Map集合中所有的key（所有的键都是一个“Set集合”）

V remove(Object key)	//通过key删除键值对,如果存在，则从该映射中移除键的映射（可选操作）

int size()	//获取Map集合中键值对的个数

import java.security.Key;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
public class Warehouse1 {
    public static void main(String[] args){
        HashMap<String,Integer> hashMap=new HashMap<>();
        hashMap.put("年龄",20);
        hashMap.put("身高",180);
        hashMap.put("体重",60);
        System.out.println("键为年龄所对应的值为:"+hashMap.get("年龄"));
        System.out.println("该map是否包含键为“年龄”？"+hashMap.containsKey("年龄"));
        System.out.println("该map是否包含键值为90？"+hashMap.containsValue(90));
        System.out.println("该map是否为空？"+hashMap.isEmpty());
        System.out.println("该map的长度大小为："+hashMap.size());
        System.out.println("移除键为“体重“的键值对"+hashMap.remove("体重"));
        System.out.println("哈希映射中的内容如下:"+hashMap);
        Set<String> keys=hashMap.keySet();
        Iterator<String> iterator=keys.iterator();
        System.out.println("hashmap中的元素如下:");
        while(iterator.hasNext()){
            String s= iterator.next();
            Integer name= hashMap.get(s);
            System.out.println(s+":"+name);
        }
    }
}

import java.security.Key;
import java.util.*;

public class Warehouse1 {
    public static void main(String[] args){
        LinkedHashMap<String,Integer> linkedHashMap=new LinkedHashMap<>();
        linkedHashMap.put("number1",10);
        linkedHashMap.put("number2",20);
        linkedHashMap.put("number3",30);
        linkedHashMap.put("number4",40);
        linkedHashMap.get("number1");
        linkedHashMap.get("number4");
        Set <Map.Entry<String,Integer>> sets=linkedHashMap.entrySet();//Map.Entry是Map的一个内部类，表达一个 key/value映射关系
        System.out.println("linkedHashMap中的元素为：");
        for(Map.Entry<String,Integer> entry:sets) {
            System.out.println("键为：" + entry.getKey() + ",值为：" + entry.getValue());
        }
           System.out.println("---------------");
           LinkedHashMap<String,Integer> linkedHashMap1=new LinkedHashMap<String,Integer>(3,0.5f,true);
            linkedHashMap1.put("number1",10);
            linkedHashMap1.put("number2",20);
            linkedHashMap1.put("number3",30);
            linkedHashMap1.put("number4",40);
            linkedHashMap1.get("number1");
            linkedHashMap1.get("number4");
            linkedHashMap1.put("number3",1000);
            Set<Map.Entry<String,Integer>> set=linkedHashMap1.entrySet();
            System.out.println("linkedHashMap1中的元素为：");
            for(Map.Entry<String ,Integer> entry1:set) {
                System.out.println("键为：" + entry1.getKey() + "值为：" + entry1.getValue());
            }
    }
}

import java.util.*;
public class Warehouse1 {
    public static void main(String[] args) {
        TreeMap<String,String> treeMap=new TreeMap<>();
        treeMap.put("水果","苹果");
        treeMap.put("汽车","奔驰");
        treeMap.put("城市","西安");
        System.out.println("映射中的元素是："+treeMap);
        Set<String> keySet=treeMap.keySet();
        Iterator<String> iterator=keySet.iterator();
        System.out.println("TreeMap类实现的Map映射，按键值升序排列元素如下：");
        while(iterator.hasNext()){
            String it=iterator.next();
            String name=treeMap.get(it);
            System.out.println(it+":"+name);
        }
    }
}

import java.util.*;
public class Warehouse1 {
    public static void main(String[] args) {
    Hashtable<String,Double> hashtable=new Hashtable<>();
    hashtable.put("王俊凯",new Double(350.55));
        hashtable.put("王源",new Double(3250.55));
        hashtable.put("易烊千玺",new Double(1350.55));
        Enumeration<String> names=hashtable.keys();
        while(names.hasMoreElements()){
            String name=names.nextElement();
            System.out.println(name+":"+hashtable.get(name));
        }
        double new_double=hashtable.get("易烊千玺").doubleValue();
        hashtable.put("易烊千玺",new Double(new_double+2000));
        System.out.println("易烊千玺的新余额为："+hashtable.get("易烊千玺"));
    }
}