Java集合的Stack、Queue、Map的遍歷

Java集合的Stack、Queue、Map的遍歷

 

在集合操做中，經常離不開對集合的遍歷，對集合遍歷通常來講一個foreach就搞定了，可是，對於Stack、Queue、Map類型的遍歷，仍是有一些講究的。

 

最近看了一些代碼，在便利Map時候，慘不忍睹，還有一些是遍歷錯誤，忽略了隊列、棧與普通Collection的差異致使的，這些代碼就不做爲反面教材了。

 

下面是經常使用的寫法：

 

1、Map的遍歷

 

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

/**
* Map的遍歷，這個遍歷比較特殊，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");

                 //最簡潔、最通用的遍歷方式
                 for (Map.Entry<String, String> entry : map.entrySet()) {
                        System.out.println(entry.getKey() + " = " + entry.getValue());
                }
                 //Java5以前的比較簡潔的便利方式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以前的比較簡潔的便利方式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

 

2、Queue的遍歷

 

import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;

/**
* 隊列的遍歷
*
* @author leizhimin 2009-7-22 15:05:14
*/
public class TestQueue {
         public static void main(String[] args) {
                Queue<Integer> q = new LinkedBlockingQueue<Integer>();
                 //初始化隊列
                 for ( int i = 0; i < 5; i++) {
                        q.offer(i);
                }
                System.out.println( "-------1-----");
                 //集合方式遍歷，元素不會被移除
                 for (Integer x : q) {
                        System.out.println(x);
                }
                System.out.println( "-------2-----");
                 //隊列方式遍歷，元素逐個被移除
                 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

 

3、Stack的遍歷

 

import java.util.Stack;

/**
* 棧的遍歷
*
* @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);
                }
                 //集合遍歷方式
                 for (Integer x : s) {
                        System.out.println(x);
                }
                System.out.println( "------1-----");
                 //棧彈出遍歷方式
//                while (s.peek()!=null) {     //不健壯的判斷方式，容易拋異常，正確寫法是下面的
                 while (!s.empty()) {
                        System.out.println(s.pop());
                }
                System.out.println( "------2-----");
                 //錯誤的遍歷方式
//                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

 

 

在遍歷集合時候，優先考慮使用foreach語句來作，這樣代碼更簡潔些。