Monday, 26 May 2014

PART 2.4

41. What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.

42. What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its implements clause.

43. What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to communicate each other.

44. What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.

45. What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.

46. What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of the class’s outer class. A static inner class does not have any object instances.

47. What is an object’s lock and which object’s have locks?
An object’s lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object’s lock. All objects and classes have locks. A class’s lock is acquired on the class’s Class object.

48. When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the referenced interface.

49. What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.

50. What do heavy weight components mean?
Heavy weight components like Abstract Window Toolkit (AWT), depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component, when it is running on the Java platform for Unix platform, it maps to a real Motif button. In this relationship, the Motif button is called the peer to the java.awt.Button. If you create two Buttons, two peers and hence two Motif Buttons are also created. The Java platform communicates with the Motif Buttons using the Java Native Interface. For each and every component added to the application, there is an additional overhead tied to the local windowing system, which is why these components are called heavyweight.

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