33 Java Interview Questions

Typical HR Questions

1. What are the thread states in java ?

2. List all the types of nested class ?

3. How to increase the heap memory of the JVM ?

4. Name three JVMs ?

5. What is the quickest type of Map ?

6. How do you redirect the System.out ( "standard" output stream ) to a file ?

7. A class that supports serializarion must implement serializable, if its base class is not serizable then what must it have. ?

8. Which method should you override when writing a Customer Class Loader ?

9. Name the standard class loaders ?

10. What is the signature of readResolve() and what is it used for ?

11. Other than using externizable, how can you handle custom serilization ?

12. In java 6, how can you see the assembly code that the JIT is creating ?

13. Name 10 Ways to Reduce Lock Contention in Threaded Programs ?

14. List 4 Collection Classes and 4 Collection Interfaces ?

15. How do you create an array using reflection

16. Describethe following exceptions : CloneNotSupportedException, ClassNotFoundException, ArrayStoreException, ClassCastException, ConcurrentModificationException, IllegalMonitorStateException, UnsupportedOperationException.

17 With java collections, whats the difference between Offer(E e) and Add(E e).

18 Can a top level class be have a protected class modifier

19 Does this produce a runtime error

public class Test {

    public static void main(String... args) {

        Object o = new Object() {
            public boolean equals(Object t) {
                return t.equals("hi");


20 What is the difference between weak and soft references

21 What is the difference between NoClassDefFoundError and a ClassNotFoundException

22 When should you use Serializable and when should you use Externalizable

23 How do you create a singleton

24 What is the difference between parameters and arguments

25 what is escape analysis

26 what are memory barriers

27 how/when does instruction reodering occur in java

28 what is object orientation

29 explain double checked locking

30 is there ever a case when a singleton may return a differnt instance

30 what is instruction reordering and when / where is it used

31 If the compareTo method of a comparable object returns zero are they equal

32 what are synthetic bridge methods

33 write a class that implements the following :

  • if the object has been seen before, returns the same integer
  • if the object has not been seen before returns a different integer.
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