1.主要掌握5个接口:
Collection List Set Map Iterator Enumeration
2.不允许重复的子接口:Set
3.Set中常用的两个子类:散列存放的子类:HashSet
顺序存放的子类TreeSet
4. Map接口
public Set<K> keySet() ,将Map中的所有key以Set集合的方式返回
public Set<Map.Entry><K,V>>entrySet(),将Map集合变为Set集合
Map的输出
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package
com.ylfeiu.utils;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Set;public class HashMapEcho { public
static void main(String[] args) { Map<Integer, String> map = new
HashMap<>(); map.put(1, "hello"); map.put(2, "txt"); map.put(2, "txt2"); map.put(null, "ylfeiu"); map.put(1, "hello"); Set<Integer> set = map.keySet(); Iterator<Integer> car = set.iterator(); while
(car.hasNext()) { Integer key = car.next(); System.err.println(key + "------------>"
+ map.get(key)); } }} |
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例子2package
com.ylfeiu.utils;import java.util.HashMap;import java.util.Hashtable;import java.util.Iterator;import java.util.Map;import java.util.Set;public
class HashMapEcho2 { public
static void main(String[] args) { Map<Integer, String> map = new
Hashtable<>(); map.put(1, "hello"); map.put(2, "txt"); map.put(2, "txt2"); // map.put(null, "ylfeiu");//HashTable不能使用null做key map.put(1, "hello"); Set<Map.Entry<Integer, String>> set = map.entrySet();//把Map.Entry当作一个对象 Iterator<Map.Entry<Integer, String>> car = set.iterator(); while
(car.hasNext()) { Map.Entry<Integer, String> me = car.next(); System.err.println(me.getKey() + "------------>"
+ me.getValue()); } }} |
原文：http://www.cnblogs.com/ylfeiu/p/3599344.html