import java.util.*;class A{
private static int counter;
private int count = counter++;
public String toString(){
return ("A : " + count);
}
}
class Test{
public static void main(String[] args){
A[] a = new A[10];
for(int i = 0;i < a.length;i ++)
a[i] = new A();
List<A> list = new ArrayList<A>(Arrays.asList(a));
System.out.println("list = " + list);
List<A> sublist = list.subList(list.size() / 4, list.size() / 2);
System.out.println("sublist = " + sublist);
list.removeAll(sublist); //为什么会出现异常???
sublist.clear(); //这里是对sublist进行clear,怎么会影响到最后list的输出呢??
System.out.println("finally : " + list);
}
}由上述注释所示。好纠结啊
private static int counter;
private int count = counter++;
public String toString(){
return ("A : " + count);
}
}
class Test{
public static void main(String[] args){
A[] a = new A[10];
for(int i = 0;i < a.length;i ++)
a[i] = new A();
List<A> list = new ArrayList<A>(Arrays.asList(a));
System.out.println("list = " + list);
List<A> sublist = list.subList(list.size() / 4, list.size() / 2);
System.out.println("sublist = " + sublist);
list.removeAll(sublist); //为什么会出现异常???
sublist.clear(); //这里是对sublist进行clear,怎么会影响到最后list的输出呢??
System.out.println("finally : " + list);
}
}由上述注释所示。好纠结啊
/**The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations supported
* by this list.<p>/ , 修改sublist能影响到list
sublist.clear();1.看api:boolean removeAll(Collection<?> c)从列表中移除指定 collection 中包含的其所有元素(可选操作)。
2.执行完removeall()完,sublist就为空了,编译器抛出(运行修改异常)ConcurrentModificationException
import java.util.*;class A{
private static int counter;
private int count = counter++;
public String toString(){
return ("A : " + count);
}
}
class aiqing{
public static void main(String[] args){
A[] a = new A[10];
for(int i = 0;i < a.length;i ++)
a[i] = new A();
List<A> lists = new ArrayList<A>(Arrays.asList(a));
System.out.println("list = " + lists);
//sublist并不是将lists分片之后在进行复制一份,而是直接在list的位置进行操作,即sublist并不是一个真正的对象
List<A> sublist = lists.subList(lists.size() / 4, lists.size() / 2);
System.out.println("sublist = " + sublist);
sublist.add(new A());
//因此,当执行add操作后,list的值也将受到影响
System.out.println("sublist add : " + lists);
//lists.removeAll(sublist); //因此这里会出现ConcurrentModificationException异常,因为你此时操作的对象一直是list
//同理,下面的操作也会影响到lists的值。
sublist.clear();
System.out.println("finally : " + lists);
}
}