Interview Questions in Java (MCQ)

In this article, we have presented several Interview Questions in Java (MCQ) covering all important topics in Java. These questions are frequently asked in Coding Interviews and you must attempt these questions.

If you need to revise Java quickly before attempting the questions, go through this article: Learn Java in one post (30 minutes) with code examples.

Following are the member variables in a standard HashMap implementation in Java:

static final int DEFAULT_INITIAL_CAPACITY = 16;
	static final int MAXIMUM_CAPACITY = 1 << 30;
	static final float DEFAULT_LOAD_FACTOR = 0.75f;

	transient Entry[] table;
	transient int size;
	int threshold;
	final float loadFactor;

In Queue collection in Java, we can remove element using two standard member functions:

Queue<String> queue=new PriorityQueue<String>();  
// add
queue.add("opengenus"); 
// remove
queue.remove();
queue.poll();

Following is a sample Java implementation of Singleton class:

// Singleton class in Java
// Part of iq.opengenus.org
public final class ClassSingleton {
    private static ClassSingleton INSTANCE;
    private String info = "Initial info class";
    
    private ClassSingleton() {
    }
    
    public static ClassSingleton getInstance() {
        if(INSTANCE == null) {
            INSTANCE = new ClassSingleton();
        }
        return INSTANCE;
    }
}

There are 4 types of References in Java. Weak Reference in Java is defined as follows:

// Creates a strong reference
Object obj = new Object();
// New Weak Reference to obj object
WeakReference<Object> softRef = new WeakReference<Object>(obj);

If an object has a strong reference, then it is never removed by the Garbage Collector. A strong reference is defined as follows:

Object obj = new Object(); // Creates a strong reference

In Java Collections, there are several variants of HashMap of which following are two variants:

Map<String, Integer> map = new HashMap<String, Integer>();

LinkedHashMap<Integer, String> lhmap = 
                 new LinkedHashMap<Integer, String>();

throw and throws are different keywords in Java and are used in different places to raise an exception.