Java garbage collection destroys objects as follows:
- Objects that nothing refers to
- Objects that nothing can refer to.
＜Set an object to ‘null’＞
If you set a variable to null, then it refers to nothing and the garbage collection destroys this object.
＜Set an object to another value＞
If you set a variable to another value, the object previously referred to becomes a target of the garbage collection.
Integer a = new Integer(1);
Integer b = new Integer(2);
a = b;
At this time, nothing refers to the instance ‘new Integer(1)’ and thus it becomes a target of the garbage collection.
＜Isolate references＞
Ａ⇔Ｂ
Ａ = null
Ｂ = null
The garbage collection targets them.
＜Can we execute a garbage collection immediately?＞
No.
You can only request a garbage collection.
When to execute it depends on JVM.
＜Request a garbage collection＞
・ System.gc();
・ Runtime.getRuntime().gc();
＜finalize method＞
A finalize method is invoked just before the garbage collection destroys an object.
A finalize method is invoked once for each object.
It is not recommended to write important procedure in a finalize method.
