13,Java LinkedList遍历的7种方法

LinkedList遍历方法

1. 一般的for循环(随机访问)遍历

int size = list.size();  
for (int i=0; i<size; i++) {  
    list.get(i);          
}  

2. for--each循环遍历

for (Integer integ:list){
 ;
}

3. 迭代器iterator遍历

for(Iterator iter = list.iterator(); iter.hasNext();)  
    iter.next();  

4. 用pollFirst()遍历
   ``
   while(list.pollFirst() != null)
   ;

5. 用pollLast()遍历
while(list.pollLast() != null)  
    ;  
6. 用removeFirst()遍历
try {  
    while(list.removeFirst() != null)  
        ;  
} catch (NoSuchElementException e) {  
}  
7. 用removeLast()遍历
try {  
    while(list.removeLast() != null)  
        ;  
} catch (NoSuchElementException e) {  
} 
实例

public class LinkedListTest {  
    public static void main(String[] args) {  
        LinkedList<Integer> llist = new LinkedList<Integer>();  
        for (int i=0; i<100000; i++)  
            llist.addLast(i);  
          
        byCommonFor(llist) ;// 通过一般for循环来遍历LinkedList  
        byForEach(llist) ;  // 通过for-each来遍历LinkedList  
        byIterator(llist) ; // 通过Iterator来遍历LinkedList  
        byPollFirst(llist) ;    // 通过PollFirst()遍历LinkedList     
        byPollLast(llist) ; // 通过PollLast()遍历LinkedList   
        byRemoveFirst(llist) ;   // 通过removeFirst()遍历LinkedList     
        byRemoveLast(llist) ; // 通过removeLast()遍历LinkedList  
    }  
      
   
    private static void byCommonFor(LinkedList<Integer> list) {// 通过一般for循环来遍历LinkedList  
        if (list == null)  
            return ;  
        long start = System.currentTimeMillis();       
        int size = list.size();  
        for (int i=0; i<size; i++) {  
            list.get(i);          
        }  
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byCommonFor------->" + total+" ms");  
    }  
      
    private static void byForEach(LinkedList<Integer> list) {// 通过for-each来遍历LinkedList  
        if (list == null)  
            return ;   
        long start = System.currentTimeMillis();         
        for (Integer integ:list)   
            ;   
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byForEach------->" + total+" ms");  
    }  
   
    private static void byIterator(LinkedList<Integer> list) {// 通过Iterator来遍历LinkedList  
        if (list == null)  
            return ;   
        long start = System.currentTimeMillis();       
        for(Iterator iter = list.iterator(); iter.hasNext();)  
            iter.next();   
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byIterator------->" + total+" ms");  
    }  
   
    private static void byPollFirst(LinkedList<Integer> list) {//通过PollFirst()遍历LinkedList     
        if (list == null)  
            return ;   
        long start = System.currentTimeMillis();  
        while(list.pollFirst() != null)  
            ;   
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byPollFirst------->" + total+" ms");  
    }  
   
    private static void byPollLast(LinkedList<Integer> list) {// 通过PollLast()遍历LinkedList   
        if (list == null)  
            return ;   
        long start = System.currentTimeMillis();  
        while(list.pollLast() != null)  
            ;   
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byPollLast------->" + total+" ms");  
    }  
   
    private static void byRemoveFirst(LinkedList<Integer> list) {// 通过removeFirst()遍历LinkedList  
        if (list == null)  
            return ;   
        long start = System.currentTimeMillis();  
        try {  
            while(list.removeFirst() != null)  
                ;  
        } catch (NoSuchElementException e) {  
        }   
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byRemoveFirst------->" + total+" ms");  
    }  
   
    private static void byRemoveLast(LinkedList<Integer> list) {// 通过removeLast()遍历LinkedList  
        if (list == null)  
            return ;  
        long start = System.currentTimeMillis();  
        try {  
            while(list.removeLast() != null)  
                ;  
        } catch (NoSuchElementException e) {  
        }  
        long end = System.currentTimeMillis();  
        long total = end - start;  
        System.out.println("byRemoveLast------->" + total+" ms");  
    }  
} 
运行结果：
byCommonFor------->5342 ms
byForEach------->11 ms
byIterator------->8 ms
byPollFirst------->4 ms
byPollLast------->0 ms
byRemoveFirst------->0 ms
byRemoveLast------->0 ms
由此可见，遍历LinkedList时，使用removeFist()或removeLast()效率最高。但用它们遍历时，会删除原始数据；若单纯只读取，而不删除，LinkedList遍历时建议使用For-each或者迭代器的方式。千万不要通过随机访问去遍历LinkedList！

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