Using Private Static Final Object Locks for Safe Java Synchronization

Use a private (static) final Object lock = new Object() to protect critical sections.

Reason

1. Do not use monitor objects whose permissions cannot be controlled.

Do not do this:

Synchronized instance methods or synchronized blocks that use this as the monitor.

Synchronized static methods that use the getClass() monitor.

2. Do not use shared monitor objects; they may cause deadlocks or uncontrolled risks.

Boolean monitor objects

Primitive type monitor objects

Autoboxed type monitor objects

new String("xxx").intern() shared monitor

String lock = "Lock" cached monitor

java.lang.Integer.valueOf(int) cached monitor

getClass() public monitor; subclasses have different monitors

Class name monitor

Class.forName() monitor

You can use the following monitor objects:

private final String lock = new String("LOCK");

private final Object lock = new Object();

3. For static data, use a static monitor object.

Do not do this:

Static data protected by a non‑static monitor.

Synchronized methods using the built‑in monitor to protect static data.

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