1 Map接口概述
l Map中的集合，元素是成對存在的(理解為夫妻)。每個元素由鍵與值兩部分組成，通過鍵可以找對所對應的值。
l Collection中的集合稱為單列集合，Map中的集合稱為雙列集合。
l 需要注意的是，Map中的集合不能包含重復的鍵，值可以重復；每個鍵只能對應一個值。
Map中常用的集合為HashMap集合、LinkedHashMap集合。
Map集合的遍歷：
1.keySet
public class Demo01 { public static void main(String[] args) { Map<Integer,String> map=new HashMap<Integer,String>(); //向map中添加鍵值對 map.put(1, "熊大"); map.put(2, "光頭強"); map.put(3, "熊二"); map.put(2, "光頭強"); //根據key獲取value System.out.println(map.get(3)); //刪除 map.remove(1); //遍歷方式1：keySet方法 Set<Integer>set=map.keySet(); for(Integer key:set){ System.out.println(map.get(key)); } Iterator<Integer>it=set.iterator(); while(it.hasNext()){ System.out.println(map.get(it.next())); } }
2.entrySet
public class Demo02 { public static void main(String[] args) { Map<Integer,String> map=new HashMap<Integer,String>(); //向map中添加鍵值對 map.put(1, "熊大"); map.put(2, "光頭強"); map.put(3, "熊二"); map.put(2, "光頭強"); //遍歷方式2：Entry Set<Map.Entry<Integer, String>>set=map.entrySet(); for(Map.Entry<Integer, String>entry:set){ System.out.println(entry.getKey()+"\t"+entry.getValue()); } } }
練習：
Iractor,for和entrySet,keySet遍歷Map集合
public class Demo04 { public static void main(String[] args) { Map<GirlFriend,String>map=new HashMap<GirlFriend,String>(); //創建對象 GirlFriend g1=new GirlFriend("吳宣儀",24,166); GirlFriend g2=new GirlFriend("楊超越",21,168); GirlFriend g3=new GirlFriend("朴孝敏",28,167); GirlFriend g4=new GirlFriend("羅玉鳳",34,165); //向map集合中添加key和value map.put(g1, "張三"); map.put(g2, "李四"); map.put(g3, "王五"); map.put(g4, "李四"); //遍歷entrySet+for Set<Map.Entry<GirlFriend,String>>set=map.entrySet(); for(Map.Entry<GirlFriend, String> entry:set){ System.out.println(entry.getKey()+"\t"+entry.getValue()); } System.out.println("==============================="); //entry+iterator Iterator<Map.Entry<GirlFriend, String>>it=set.iterator(); while(it.hasNext()){ Map.Entry<GirlFriend, String>ent=it.next(); System.out.println(ent.getKey()+"\t"+ent.getValue()); } } }
public class Demo03 { public static void main(String[] args) { Map<GirlFriend,String>map=new HashMap<GirlFriend,String>(); //創建對象 GirlFriend g1=new GirlFriend("吳宣儀",24,166); GirlFriend g2=new GirlFriend("楊超越",21,168); GirlFriend g3=new GirlFriend("朴孝敏",28,167); GirlFriend g4=new GirlFriend("羅玉鳳",34,165); //向map集合中添加key和value map.put(g1, "張三"); map.put(g2, "李四"); map.put(g3, "王五"); map.put(g4, "李四"); //KeySet+for Set<GirlFriend>set=map.keySet(); for(GirlFriend g:set){ System.out.println(g+"\t"+map.get(g)); } System.out.println("==================================================="); //KeySet+iterator Iterator<GirlFriend>it=set.iterator(); while(it.hasNext()){ GirlFriend gg=it.next(); System.out.println(gg+"\t"+map.get(gg)); } } }