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Java Articles » Class » Synchronized

1. Double-checked locking: Clever, but broken javaworld.com

Unfortunately, synchronized methods run much slower -- as much as 100 times slower -- than ordinary unsynchronized methods. One of the motivations for lazy initialization is efficiency, but it appears that in order to achieve faster program startup, you have to accept slower execution time once the program starts. That doesn't sound like a great trade-off.

2. Understand that for instance methods, synchronized locks objects, not methods or code ibm.com

For instance methods, the synchronized keyword does not lock a method or code; it locks objects. Remember that there is only one lock associated with each object.

3. Use synchronized or volatile when accessing shared variables ibm.com

When variables are shared between threads, they must always be accessed properly in order to ensure that correct and valid values are manipulated. The JVM is guaranteed to treat reads and writes of data of 32 bits or less as atomic. This might lead some programmers to believe that access to shared variables does not need to be synchronized or the variables declared volatile . Consider this code:

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