Java Interview Questions - Question Set 1

Thursday, September 23, 2010

Java Interview Questions

1. Why a thread blocks or enters to waiting state on I/O?
A Threads enters to waiting state or block on I/O because other threads can execute while the I/O operations are performed.

2. What are transient variables in java?
A Transient variables are variable that cannot be serialized.

3. How Observer and Observable are used?
A Subclass of Observable class maintains a list of observers. Whenever an Observable object is updated, it invokes the update () method of each of its observers to notify the observers that it has a changed state. An observer is any object that implements the interface Observer.

4. what is List interface?
A List is an ordered collection of objects.

5. What is a Vector?
A Vector is a global array of objects.

6. What is the difference between yield () and sleep ()?
A When a object invokes yield () it returns to ready state. But when an object invokes sleep () method enters to not ready state.

7. What are Wrapper Classes?
A They are wrappers to primitive data types. They allow us to access primitives as objects.

8. Can we call finalize () method?
A Yes. Nobody will stop us to call any method, if it is accessible in our class. But a garbage collector cannot call an object’s finalize method if that object is reachable.

9. What is the difference between time slicing and preemptive scheduling?
A In preemptive scheduling, highest priority task continues execution till it enters a not running state or a higher priority task comes into existence. In time slicing, the task continues its execution for a predefined period of time and reenters the pool of ready tasks.

10. What is the initial state of a thread when it is created and started?
A The thread is in ready state.


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