为什么会出现 java.util.ConcurrentModificationException 异常？

在Map或者Collection的时候，不要用它们的API直接修改集合的内容（否则会出现 java.util.ConcurrentModificationException 异常），如果要修改可以用Iterator的remove()方法，例如：

 1 public void setReparation( Reparation reparation ) {   
 2      for (Iterator it = this.reparations.iterator();it.hasNext();){    //reparations为Collection   
 3          Reparation repa = (Reparation)it.next();   
 4          if (repa.getId() == reparation.getId()){   
 5              this.reparations.remove(repa);   
 6              this.reparations.add(reparation);   
 7          }   
 8      }   
 9 }  
10 

如上写会在运行期报ConcurrentModificationException，可以如下修改：

 1 public void setReparation( Reparation reparation ) {   
 2     boolean flag = false;   
 3     for (Iterator it = this.reparations.iterator();it.hasNext();){    //reparations为Collection   
 4         Reparation repa = (Reparation)it.next();   
 5         if (repa.getId() == reparation.getId()){   
 6             it.remove();   
 7             flag = true;   
 8             break;   
 9         }   
10     }   
11     if(flag){   
12       this.reparations.add(reparation);   
13     }   
14 }  
15 

转自:http://www.javaeye.com/topic/124788