Wednesday, September 26, 2007

Java Interview Questions

Question: Why Java does not support multiple inheritence ?
Java DOES support multiple inheritance via interface implementation.

Question:What is the difference between final, finally and finalize?
o final - declare constant
o finally - handles exception
o finalize - helps in garbage collection

Question: Where and how can you use a private constructor.
Private constructor can be used if you do not want any other class to instantiate the object , the instantiation is done from a static public method, this method is used when dealing with the factory method pattern when the designer wants only one controller (fatory method ) to create the object.

Question: In System.out.println(),what is System, out and println, pls explain?
System is a predefined final class,out is a PrintStream object and println is a built-in overloaded method in the out object.

Question: What is meant by "Abstract Interface"?
First, an interface is abstract. That means you cannot have any implementation in an interface. All the methods declared in an interface are abstract methods or signatures of the methods.

Question: Can you make an instance of an abstract class? For example - java.util.Calender is an abstract class with a method getInstance() which returns an instance of the Calender class.
No! You cannot make an instance of an abstract class. An abstract class has to be sub-classed. If you have an abstract class and you want to use a method which has been implemented, you may need to subclass that abstract class, instantiate your subclass and then call that method.

Question: What is the difference between Swing and AWT components?
AWT components are heavy-weight, whereas Swing components are lightweight. Heavy weight components 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.

Question: Why Java does not support pointers?
Answer: Because pointers are unsafe. Java uses reference types to hide pointers and programmers feel easier to deal with reference types without pointers. This is why Java and C# shine.

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