Java Interview Questions - Page 1
Java Interview Questions by Inigo Nirmal
Question: Can a private method of a superclass be declared within a subclass?Answer: Sure. A private field or method or inner class belongs to its declared class and hides from its subclasses. There is no way for private stuff to have a runtime overloading or overriding (polymorphism) features.
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.