Java Interview Questions - Page 1

Java Interview Questions by Inigo Nirmal

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 instanstiate 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 output of x<y? a:b = p*q when x=1,y=2,p=3,q=4?
Answer: When this kind of question has been asked, find the problems you think is necessary to ask before you give an answer. Ask if variables a and b have been declared or initialized. If the answer is yes. You can say that the syntax is wrong. If the statement is rewritten as: x<y? a:(b=p*q); the return value would be variable a because the x is 1 and less than y = 2; the x < y statement return true and variable a is returned.

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.