使用Enumeration和Iterator遍历集合类详解

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map.Entry;

//一个遍历hashtable实例
public class TraveseHashTable {
    public static void main(String[] args) {
        //初始化创建hashtable
        Hashtable<String, String> ht = new Hashtable<String, String>();
        for (int i = 0; i < 10000; i++) {
            ht.put("Key=" + i, "Val=" + i);
        }

        // 1. 使用Enumeration
        long start = System.currentTimeMillis();
        Enumeration<String> en = ht.keys();//使用枚举获取key
        while (en.hasMoreElements()) {
            en.nextElement();
        }
        long end = System.currentTimeMillis();
        System.out.println("Enumeration keys costs " + (end - start)
                + " milliseconds");

        // 2. 使用Enumeration
        start = System.currentTimeMillis();
        Enumeration<String> en2 = ht.elements();//使用枚举获取这个key-value对
        while (en2.hasMoreElements()) {
            en2.nextElement();
        }
        end = System.currentTimeMillis();
        System.out.println("Enumeration elements costs " + (end - start)
                + " milliseconds");

        // 3. Iterator
        start = System.currentTimeMillis();
        Iterator<String> it = ht.keySet().iterator();//使用迭代器获取这个key
        while (it.hasNext()) {
            it.next();
        }
        end = System.currentTimeMillis();
        System.out.println("Iterator keySet costs " + (end - start)
                + " milliseconds");

        // 4. Iterator
        start = System.currentTimeMillis();
        Iterator<Entry<String, String>> it2 = ht.entrySet().iterator();//使用迭代器获取这个key-value对
        while (it2.hasNext()) {
            it2.next();
        }
        end = System.currentTimeMillis();
        System.out.println("Iterator entrySet costs " + (end - start)
                + " milliseconds");

    }
}