Interview Questions

Purpose of these questions (please share this with candidate):

When we interview developers, we have discussions focused on Java and object-oriented design to determine the skill level of a candidate. We don't treat these as tests, nor do we look at the outcome in a pass/fail light. This is simply one more piece of information used in the evaluation process. Please feel free to ask questions and comment on the process.

Java Specific

1. Describe the difference between an int and an Integer in Java. When would you use an int, and when would you use an Integer?

2. Describe the process of garbage collection in Java. When does an object become a candidate for garbage collection? How do you force the garbage collection process to begin?

In the following graph, if object 3 is removed, what other objects will become candidates for garbage collection?

3. Describe the difference between method overloading and method overriding. Is it possible to overload a static method? Is it possible to override a static method? Talk about the difference between overriding and hiding.

In the following code, explain what the output will be.

public class Base {
    public void f() {
        System.out.println("Base.f()");
    }

    public static void g() {
        System.out.println("Base.g()");
    }
}

public class Child extends Base {
    public void f() {
        System.out.println("Child.f()");
    }

    public static void g() {
        System.out.println("Child.g()");
    }
}

public class Tester {
    public static void main(String[] pArgs) {

        Base lObj = new Child();

        lObj.f();
        lObj.g();
    }
}

4. Describe a way to create a Thread in Java. Describe another way. What is the first method to be executed on a new Thread (excluding the constructor and any methods invoked by constructors)?

5. Describe the life cycle of a servlet. Which methods can be called more than once by the container for a particular servlet class?

General Software Concepts

6. In the following simple class, identify any method that is not thread safe. Describe the problem(s), and suggest ways that they could be solved.

public class Simple {

    protected int mMember = 0;

    public void f(int pParam) {
        int lValue = 5;
        lValue = lValue + pParam;
        System.out.println("f computed " + lValue);
    }

    public void g(int pParam) {
        int lValue = 1;
        mMember += lValue * pParam;
        System.out.println("g computed " + mMember);
    }
}

7. Two interfaces are defined to represent a binary tree. A binary tree is a tree in which each node can have at most two children. Write the implementation for the method Node.traverse() and the method Tree.traverse(). The methods should implement a depth first traversal of a given tree. Tree.traverse() should be less than three lines of code, and Node.traverse() should be less than ten.

Figure 1: Order in which Node.operate() is called during a DFS

public interface INode {
    // These methods return null if there is no child node
    public INode getLeftChild();
    public INode getRightChild();

    /**
     * Traverse this node.
     * @return void
     */
    public void traverse();

    public void operate();
}

public interface ITree {

    public INode getRootNode();

    /**
     * DFS traverse the tree from the root node.
     */
    public void traverse();
}

Figure 2: Definition of interfaces INode and ITree

Following is a code snippet illustrating how the ITree interface might be used to traverse a tree:

public void f() {

    // get a tree in some magical way
    ITree myTree = getTree();

    // traverse the entire tree, starting from the root node
    myTree.traverse();
}

Figure 3: Example of using ITree and INode.

Experience Based Questions

8. What are design patterns? Why are design patterns useful? Describe a design pattern that you have used in the past.

9. What kept you awake at night in your last job/project?

10. Describe a development process/methodology that you are familiar with (e.g., XP, RUP, etc.). Do you have strong opinions about which of these is best?