Map集合，将key对象映射到value对象
三个主要的子类：Hashtable，HashMap，TreeMap
Hashtable：底层是哈希表数据结构，不允许使用null值，线程同步
HashMap：底层是哈希表数据结构，允许使用null值，线程不同步
TreeMap：底层是二叉树数据结构，线程不同步，可以用于给Map集合中的键排序
使用keySet()方法遍历Map集合
调用Map对象的keySet()方法，得到Set对象，这里存储的是所有的键
import java.util.HashMap; java.util.Map; java.util.Set; java.util.TreeMap; public class MapDemo { /** * @param args */ static void main(String[] args) { Map<String,String> map=new HashMap<String,String>(); map.put("name","taoshihan"); map.put("age","100"); map.put("gender","female"); Set<String> keySet=map.keySet(); for(String key:keySet){ System.out.println(map.get(key)); } //TreeMap可排序 Map<StudentTreeMap,String> treeMap=new TreeMap<StudentTreeMap,1)">(); treeMap.put(new StudentTreeMap("taoshihan1",40),"陶士涵"); treeMap.put(new StudentTreeMap("taoshihan2",30),"陶士涵2"new StudentTreeMap("taoshihan3",50),"陶士涵3"); Set<StudentTreeMap> treeMapSet=treeMap.keySet(); (StudentTreeMap key:treeMapSet){ System.out.println(key.name+"====="+key.age); } } } class StudentTreeMap implements Comparable<StudentTreeMap>{ int age; public String name; public StudentTreeMap(String name, age) { this.name=name; this.age=age; } @Override compareTo(StudentTreeMap o) { if(o.age<this.age){ return 1; }else{ return -1; } } }
