Java Language Interview Question and Answers : 5

21.	What are wrapper classes?
	primitive data types may be converted into object types by using the wrapper classes contained in the java.lang package. Exampes : int, float, long, char, double

22.	What is the difference between an instance variable and a static variable?
	Class variables are called static variables. There is only one occurrence of a class variable per JVM per class loader.When a class is loaded the class variables are initialized. Instance variables are non-static and there is one occurrence of an instance variable in each class instance.Also known as a member variable or a field.

23	Where and how can you use a private constructor?
	Private constructor is used if you do not want other classes to instantiate the object and to prevent subclassing.The instantiation is done by a public static method (i.e. a static factory method) within the same class.

24.	What is type casting?
	Type casting means treating a variable of one type as though it is another type. Examples : int m = 5; byte n =i;

25.	What is a user defined exception?
	User defined exceptions may be implemented by defining a new exception class by extending the Exception class. <<<PREV                                                                                              NEXT>>>