Java集合的Stack、Queue、Map的遍历

Java集合的Stack、Queue、Map的遍历

 

在集合操作中，常常离不开对集合的遍历，对集合遍历一般来说一个foreach就搞定了，但是，对于Stack、Queue、Map类型的遍历，还是有一些讲究的。

 

最近看了一些代码，在便利Map时候，惨不忍睹，还有一些是遍历错误，忽略了队列、栈与普通Collection的差别导致的，这些代码就不作为反面教材了。

 

下面是常用的写法：

 

一、Map的遍历

 

import java.util.Iterator;
import java.util.Map;

/**
* Map的遍历，这个遍历比较特殊，有技巧
*
* @author leizhimin 2009-7-22 15:15:34
*/
public class TestMap {
        public static void main(String[] args) {
                Map<String, String> map = new HashMap<String, String>();
                map.put("1", "a");
                map.put("2", "b");
                map.put("3", "c");

                //最简洁、最通用的遍历方式
                for (Map.Entry<String, String> entry : map.entrySet()) {
                        System.out.println(entry.getKey() + " = " + entry.getValue());
                }
                //Java5之前的比较简洁的便利方式1
                System.out.println("----1----");
                for (Iterator<Map.Entry<String, String>> it = map.entrySet().iterator(); it.hasNext();) {
                        Map.Entry<String, String> entry = it.next();
                        System.out.println(entry.getKey() + " = " + entry.getValue());
                }
                //Java5之前的比较简洁的便利方式2
                System.out.println("----2----");
                for (Iterator<String> it = map.keySet().iterator(); it.hasNext();) {
                        String key = it.next();
                        System.out.println(key + " = " + map.get(key));
                }
        }
}

 

3 = c
2 = b
1 = a
----1----
3 = c
2 = b
1 = a
----2----
3 = c
2 = b
1 = a

Process finished with exit code 0

 

二、Queue的遍历

 

import java.util.concurrent.LinkedBlockingQueue;

/**
* 队列的遍历
*
* @author leizhimin 2009-7-22 15:05:14
*/
public class TestQueue {
        public static void main(String[] args) {
                Queue<Integer> q = new LinkedBlockingQueue<Integer>();
                //初始化队列
                for (int i = 0; i < 5; i++) {
                        q.offer(i);
                }
                System.out.println("-------1-----");
                //集合方式遍历，元素不会被移除
                for (Integer x : q) {
                        System.out.println(x);
                }
                System.out.println("-------2-----");
                //队列方式遍历，元素逐个被移除
                while (q.peek() != null) {
                        System.out.println(q.poll());
                }
        }
}

 

-------1-----
0
1
2
3
4
-------2-----
0
1
2
3
4

Process finished with exit code 0

 

三、Stack的遍历

 

/**
* 栈的遍历
*
* @author leizhimin 2009-7-22 14:55:20
*/
public class TestStack {
        public static void main(String[] args) {
                Stack<Integer> s = new Stack<Integer>();
                for (int i = 0; i < 10; i++) {
                        s.push(i);
                }
                //集合遍历方式
                for (Integer x : s) {
                        System.out.println(x);
                }
                System.out.println("------1-----");
                //栈弹出遍历方式
//                while (s.peek()!=null) {     //不健壮的判断方式，容易抛异常，正确写法是下面的
                while (!s.empty()) {
                        System.out.println(s.pop());
                }
                System.out.println("------2-----");
                //错误的遍历方式
//                for (Integer x : s) {
//                        System.out.println(s.pop());
//                }
        }
}

 

0
1
2
3
4
------1-----
4
3
2
1
0
------2-----

Process finished with exit code 0

 

 

在遍历集合时候，优先考虑使用foreach语句来做，这样代码更简洁些。

转载:http://lavasoft.blog.51cto.com/62575/181781