Java Interview Questions

“What is the difference between an interface an an abstract class in Java?”

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“HashMap implementation”

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“specific technical background”

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“Can you write a program to extract data from 4X4 array of strings ?”

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“What programming language you are comfortable in ?”

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“What is encapsulation”

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“5. The user of this class expected the output “Num: 1000000”. They got something else. What went wrong and how would you fix it?

public class Test
{
    public final static int NUMTHREADS = 1000;
    public final static int NUMLOOP = 1000;
    public static int num = 0;

    static class Mythread extends Thread
    {
        @Override
        public void run()
        {
            for (int i = 0; i < NUMLOOP; i++)
            {
                ++num;
            }
        }
    }

    public static void main(String argv[])
    {
        Mythread threads[] = new Mythread[NUMTHREADS];
        for (int i = 0; i < NUMTHREADS; ++i)
        {
            threads[i] = new Mythread();
            threads[i].start();
        }

        try
        {
            for (int i = 0; i < NUMTHREADS; ++i)
            {
                threads[i].join();
            }
        }
        catch (InterruptedException e)
        {
        }
        System.out.println("Num: " + num);
    }
}”

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“4. Implement a basic Thread Pool in Java. When it’s completed, discuss the trade offs of your implementation. If you had unlimited time, discuss what improvements you would make to it and how these improvements would help developers that used your thread pool.”

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“2. Implement the following interface to implement a binary search tree in Java

public interface BinaryTree<T extends Comparable<? super T>>
{
    public void insert(T data);
    public T findMin();
    public boolean contains(T data);
    public void remove(T data);
}

2.1. (optional) What does T extends Comparable< super T>> mean?
Ans: It means that T has to be of type Comparable, which can avoid redundantly specifying type parameters”

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