Many talented individuals have spent a great deal of time pondering ways to make double-checked locking work in order to improve performance. None have succeeded.
Double-checked locking is an incorrect idiom that does not achieve the intended effect.
Such as below
if (fitz == null) {
synchronized (this) {
if (fitz == null)

}
}
return fitz;
The programmer wants to guarantee that only one Fitzer() object is ever allocated, but does not want to pay the cost of synchronization every time this code is called. This idiom is known as double-checked locking.
Unfortunately, it does not work, and multiple Fitzer() objects can be allocated
To fix this issue by removing the first checking.