七郎's JavaBlog

在對(duì)一個(gè)map進(jìn)行迭代遍歷并刪除一些符合條件的鍵值對(duì)的時(shí)候，容易出現(xiàn)

 java.util.ConcurrentModificationException 這個(gè)異常。
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:787)
at java.util.HashMap$KeyIterator.next(HashMap.java:823)

解決辦法如下：

import java.util.*;

public class TestMap {
   public TestMap() {
   }

   public static void main(String[] args) {
     java.util.Map m = new java.util.HashMap();
     m.put("aaa", "lizongbo ");
     m.put("bbb", " lizongbo");
     m.put("ccc", "lizongbo   ");
     m.put("ddd", "   lizongbo");
     m.put("eee", "lizongbo");
     m.put("fff", "lizongbo");
     m.put("ggg", "lizongbo");
     m.put("adads", "lizongbo");
     m.put("dffd", "lizongbo");
     m.put("dcxv", "lizongbo");
     m.put("lizongbo", "lizongbo");
     m.put("ert", "lizongbo");
     m.put("544", "lizongbo ");
     Iterator iterator = m.keySet().iterator();
     while (iterator.hasNext()) {
       String sessionId = (String) iterator.next();
       if ("ggg".equals(sessionId) || "lizongbo".equals(sessionId) ||
           "544".equals(sessionId)) {
            m.remove(sessionId);
            iterator.remove();        //這行代碼是關(guān)鍵,使循環(huán)知道m(xù)大小已經(jīng)改變        
       }
     }
     System.out.println(m.get("ggg"));
     System.out.println(m.get("lizongbo"));
     System.out.println(m.get("544"));
   }