sebb schrieb:
On 26/09/2009, ohe...@apache.org <ohe...@apache.org> wrote:
Author: oheger
Date: Sat Sep 26 14:27:32 2009
New Revision: 819141
URL: http://svn.apache.org/viewvc?rev=819141&view=rev
Log:
[LANG-496] Added LazyInitializer class plus test class.
Added:
commons/proper/lang/trunk/src/java/org/apache/commons/lang/concurrent/LazyInitializer.java
(with props)
commons/proper/lang/trunk/src/test/org/apache/commons/lang/concurrent/
commons/proper/lang/trunk/src/test/org/apache/commons/lang/concurrent/LazyInitializerTest.java
(with props)
<snip/>
+ /** Stores the managed object. */
+ private volatile T object;
+
+ /**
+ * Returns the object wrapped by this instance. On first access the object
+ * is created. After that it is cached and can be accessed pretty fast.
+ *
+ * @return the object initialized by this {...@code LazyInitializer}
+ */
+ public T get() {
+ T result = object;
+
+ if (result == null) {
+ synchronized (this) {
+ result = object;
+ if (result == null) {
+ object = result = initialize();
+ }
+ }
+ }
+
+ return result;
+ }
Is the temporary variable "result" needed?
Would it not be simpler to do the following:
private volatile T object;
public T get() {
if (object == null) {
synchronized (this) {
if (object == null) {
object = initialize();
}
}
}
return object;
}
Or maybe I'm missing some subtlety here ?
In which case it should be documented in a comment please.
<snip/>
According to Bloch's book the temporary variable is indeed a performance
optimization. It prevents that the volatile field is read twice in the
common case that the object has already been initialized.
It's a good idea to add a comment. Will do.
Oliver
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