Java Interview Questions

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

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

Question: Where and how can you use a private constructor.
Answer: 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?
Answer: 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"?
Answer: 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.
Answer: 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?
Answer: 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.