Java集合的Stack、Queue、Map的遍历

一、Map的遍历

 

import java.util.HashMap; 
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.Queue; 
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

 

import java.util.Stack; 

/** 

* 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。