Guarding on a non-final field may result in unexpected race conditions, as locks will be held on the value of the field (which may change), rather than the field itself.

Example:

    private ReadWriteLock lock = new ReentrantReadWriteLock(); //not final guarding field
    private Object state;

    @GuardedBy("lock")
    public void bar() {
        state = new Object();
    }

Supported @GuardedBy annotations are:

• net.jcip.annotations.GuardedBy
• javax.annotation.concurrent.GuardedBy
• org.apache.http.annotation.GuardedBy
• com.android.annotations.concurrency.GuardedBy
• androidx.annotation.GuardedBy
• com.google.errorprone.annotations.concurrent.GuardedBy