3.Garbage Collection

1.
Objects passed to the method are never garbage collected in that method. So p cannot be GCed.
x is not an object.
"abc" is a string literal which goes to the string pool and is not GCed.
So, only a is eligible for GC.

2. 注意方法中的參數是primitive, String ,還是Object
 2.1 如是primitive, String  通過方法後,其值不變,因為方法中改變的是方法的行參(只是一個備份而已)
 2.2 如是Object ,就要注意方法中的操作是否改變了Object的屬性,這種改變是有效的修改了Object屬性最終值

3
Simply put, there is no guarantee which thread will run when and for how much time.
In some OSs like Windows, CPU time is given to threads in ratio of there priority in some OSs like Unix a lower priority thread executes only after higher priority thread ends.
4
Java does not have a keyword name delete.
An object is only eligible for garbage collection if the only references to the object are from other objects that are also eligible for garbage collection. Therefore, if an object obj2 is eligible for garbage collection and obj1 contains a reference to it, then obj1 must also be eligible for garbage collection.
An object will not necessarily be garbage collected immediately after the last reference to the object has been removed. It depends on when the GC thread gets a chance to run. Many a times it happens that GC doesn't run for the whole life time of the program.
Circular references generally do not prevent objects from being garbage collected.
An object is not eligible for garbage collection as long as the object can be reached from the active part of the program.
An object that has been eligible for garbage collection may stop being eligible and return to normal life. This occurs if the call to the finalize() method re-establishes a reference from the active part of the program to the object.
if an object is resurrected in finalize() then it will never be finalized again.
5.
The Java language does not specify how soon a finalizer will be invoked, except to say that it will happen before the storage for the object is reused.
Also, the Java language does not specify which thread will invoke the finalizer for any given object.
If an uncaught exception is thrown during the finalization, the exception is ignored and finalization of that object terminates.