corejava9

41. What are the basic differences between Hashtable and HashMap?
 Hashtable is a legacy class and present from JDK 1, HashMap was added later.

 Hashtable is synchronized and slower but HashMap is not synchronized and faster.

 Hashtable doesn't allow null keys but HashMap allows one null key.

42. What is the basic difference between Comparator and Comparable in Java? 

The Comparable interface is used to define the natural order of object whereas Comparator is used to define custom order. Comparable can be always one, but we can have multiple comparators to define customized order for objects.

43.Does Java have pointers?

No. Not even implicit one’s. Java has references.

Difference between reference in Java and pointer in C++:

i)References store an address. That address is the address  in memory of the object. If you were to look at that address in memory you would see the details of the object.  Pointers in C++, however, point directly to the object.

ii)You can not perform arithmetic operations on references. So, adding 1 to a reference and moving to the next reference is not possible in java, but is possible for pointers  in C++.

44. Does Java have an XOR operator? If so, what is the representation for XOR in Java?

Yes, Java does have an XOR (Exclusive Or) operator – it is represented by the caret character – the “^”.

45. If there is an exception in finalize method, will the object be garbage collected?

Yes,exception in finalize class doesn't prevent GC.