31. Can you give few examples of final classes defined in Java API?
java.lang.String, java.lang.Math are final classes.
32. How is final different from finally and finalize()?
final is a modifier which can be applied to a class or a method or a variable. final class can't be inherited, final method can't be overridden and final variable can't be changed.
finally is an exception handling code section which gets executed whether an exception is raised or not by the try block code segment.
finalize() is a method of Object class which will be executed by the JVM just before garbage collecting object to give a final chance for resource releasing activity.
33. Can a class be declared as static?
We can not declare top level class as static, but only inner class can be declared static.
public class Test
{
static class InnerClass
{
public static void InnerMethod()
{ System.out.println("Static Inner Class!"); }
}
public static void main(String args[])
{
Test.InnerClass.InnerMethod();
}
}
//output: Static Inner Class!
34. When will you define a method as static?
When a method needs to be accessed even before the creation of the object of the class then we should declare the method as static.
35. What are the restriction imposed on a static method or a static block of code?
A static method should not refer to instance variables without creating an instance and cannot use "this" operator to refer the instance.
36. I want to print "Hello" even before main() is executed. How will you acheive that?
Print the statement inside a static block of code. Static blocks get executed when the class gets loaded into the memory and even before the creation of an object. Hence it will be executed before the main() method. And it will be executed only once.
37. What is the importance of static variable?
static variables are class level variables where all objects of the class refer to the same variable. If one object changes the value then the change gets reflected in all the objects.
38. Can we declare a static variable inside a method?
Static varaibles are class level variables and they can't be declared inside a method. If declared, the class will not compile.
39. What is an Abstract Class and what is it's purpose?
A Class which doesn't provide complete implementation is defined as an abstract class=Abstract classes enforce abstraction.
40. Can a abstract class be declared final?
Not possible. An abstract class without being inherited is of no use and hence will result in compile time error.
Core Java Questions and Answer for Interview