java.lang.ClassCastException: Creating a synchronized Linked List

问题

I want a synchronized LinkedList with a Generic Class A, here the relevant parts:

public abstract class A<T extends B> implements Runnable {

And the interface for B, where the "real" B, will be a supclass

public interface B{

Following setup will throw a runtime error:

LinkedList<A<? extends B>> eopList = (LinkedList<A<? extends B>>) Collections
            .synchronizedCollection(new LinkedList<A<? extends B>>());

I've found the following proposal, but it also won't compile:

LinkedList<A<? extends B>> eopList = (LinkedList) Collections
            .synchronizedCollection(new LinkedList<A<? extends B>>());

This Is the Log:

Exception in thread "main" java.lang.ClassCastException: java.util.Collections$SynchronizedCollection cannot be cast to java.util.LinkedList

回答1:

Use Collections.synchronizedList() method instead. The method returns a List<T>. So, make the type on LHS as List, to avoid typecast:

List<A<? extends B>> eopList = Collections.synchronizedList(new LinkedList<A<? extends B>>());

回答2:

In the words of nos on Is LinkedList thread-safe when I'm accessing it with offer and poll exclusively?:

LinkedList is not thread safe. You'll have to do the locking yourself.

Try ConcurrentLinkedQueue or LinkedBlockingDeque instead if it fits your needs

or try this code from Piyush Hari's answer:

  LinkedList<A<? extends B>> eopList = (LinkedList)Collections.synchronizedList(new LinkedList<A<? extends B>());

来源：https://stackoverflow.com/questions/19510360/java-lang-classcastexception-creating-a-synchronized-linked-list