I get the following error :
Exception in thread "main" java.lang.ClassCastException
at java.util.concurrent.atomic.AtomicReferenceFieldUpdater$AtomicReferenceFieldUpdaterImpl.<init>(AtomicReferenceFieldUpdater.java:336)
at java.util.concurrent.atomic.AtomicReferenceFieldUpdater.newUpdater(AtomicReferenceFieldUpdater.java:109)
at org.telegram.bot.util.FieldTimer.<init>(FieldTimer.java:27)
at org.telegram.bot.util.FieldTimer.<init>(FieldTimer.java:19)
at org.telegram.bot.util.FieldTimer.main(FieldTimer.java:50)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
when using AtomicReferenceFieldUpdater
for generic types.
I'am totally confused and I have no idea why I'm getting such an error.
the code I am using :
public final class FieldTimer<V> {
private volatile V value;
private final V defaultValue;
private final long resetTimeout;
private final AtomicLong lastSet;
private final AtomicReferenceFieldUpdater<FieldTimer, V> updater;
public FieldTimer(V value, Class<V> type, long resetTimeout, TimeUnit unit) {
this(value, value, type, resetTimeout, unit);
}
public FieldTimer(V value, V defaultValue, Class<V> type, long resetTimeout, TimeUnit unit) {
this.value = value;
this.defaultValue = defaultValue;
this.resetTimeout = unit.toMillis(resetTimeout);
lastSet = new AtomicLong(System.currentTimeMillis());
updater = AtomicReferenceFieldUpdater.newUpdater(FieldTimer.class, type, "value");
}
public V get() {
return System.currentTimeMillis() - lastSet.get() >= resetTimeout
? defaultValue
: value;
}
public void set(V value) {
updater.set(this, value);
lastSet.set(System.currentTimeMillis());
}
public boolean compareAndSet(V expect, V update) {
boolean set = updater.compareAndSet(this, expect, update);
if (set) {
lastSet.set(System.currentTimeMillis());
}
return set;
}
}
the exception occurs in this line of code :
updater = AtomicReferenceFieldUpdater.newUpdater(FieldTimer.class, type, "value");
but, if I change it to something like this :
public final class LongFieldTimer {
private volatile Long value;
...
public LongFieldTimer(Long value, Long defaultValue, long resetTimeout, TimeUnit unit) {
...
updater = AtomicReferenceFieldUpdater.newUpdater(LongFieldTimer.class, Long.class, "value");
}
}
then there would be no errors :| (but why???)
what causes this problem? and how to solve it?
Thanks.
Your field
private volatile V value;
is of type Object
because of type erasure. The javadoc of AtomicReferenceFieldUpdater#newUpdater
states that it throws
ClassCastException
- if the field is of the wrong type
You've presumably passed Long.class
or long.class
as an argument for the type
parameter. It expects Object.class
.
In your second example, the field is explicitly defined as being of type Long
private volatile Long value;
so Long.class
will work, since that is the type of the field expected.