Coding - What is wrong? Archives

Blog Archives

01: What is wrong with following Java code snippets? Auto-unboxing, switch, short circuit & exception

Auto-unboxing, switch, short circuit logical operators & exception handling are core Java basics that sometimes lead to obscure errors if not understood well & often tested in coding tests.

Q1. What is wrong with this code?

public class WhatIsWrong {

    public static void main(String[] args) {

        double i = 2;

        switch (i) {
            case 1: System.out.println("First

…

03: What is wrong with this code? Data types & equals( ) Vs, hashCode( ) contract

Q6. What is wring with this code?

public class WhatIsWrong {

    public static void main(String args[]) {

        float sum = 0;
        while (sum != 1.0) { 
            sum += 0.1;
        }
        System.out.print("The sum is: "+sum);

    }
}

public class WhatIsWrong {

public static void main(String args[]) {

float sum = 0;

while (sum !=

…

04: What is wrong with this code? Java Collection & ConcurrentModificationException

Q9. What is wring with this code?

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class WhatIsWrong {

    public static void main(String args[]) {
        List<String> myList = new ArrayList<String>();

        myList.add("Java");
        myList.add("JEE");
        myList.add("XML");

        Iterator<String> it = myList.iterator();
        while (it.hasNext()) {
            String value = it.next();
            System.out.println("List Value:" + value);
            if (value.equals("Java")) {
                myList.remove(value);
            }
        }
    }
}

import java.

…

05: What is wrong with this code? Deep Vs Shallow comparison & multithreading

Q10 What is wring with this code?

import java.util.Date;

public class WhatIsWrong {

    public static void main(String args[]) {
        Date date1 = new Date();
        Date date2 = new Date(date1.getTime());

        if(date1 == date2){
            System.out.println("Dates match, so process it");
        }
    }
}

import java.

…

06: What is Wrong with this code? Multithreading & wait/notify

An excellent written test question to assess your Java multi-threading knowledge. Please practice it by doing it yourself.

Q. Review the code shown below and then answer the following questions.

import java.util.ArrayList;
import java.util.ArrayList;
import java.util.List;

public class WhatIsWrong {

    private static final int PRODUER_WAIT = 3;
    private static final int CONSUMER_WAIT = 2;
    private static boolean isDone = false;

    public static void main(String[] args) throws InterruptedException {
        List<Integer> list = new ArrayList<>();
        Producer prod = new Producer(list);
        Consumer cons = new Consumer(list);
        prod.start();

…

07: What is wrong with this code? Multithreading & locks

Q. What is wrong with the following Java code? Explain what does the following code do? Explain if there is anything wrong with the following code? If there is something…

Members Only Content

…

08: What is wrong with this code? Generics

Q. Can you review the following code and see if it has any issues?

import java.util.Iterator;
import java.util.NoSuchElementException;

public class WhatIsWrong {

    public static void main(String[] args) {
        MyStack<String> stack = new MyStack<String>(10000);
        for (int i = 0; i < 10000; i++) {
            stack.push("number=" + i);
        }

        while (!stack.isEmpty()) {
            stack.pop();

…

09: What is wrong with this code? HashMap & Race condition

Q. What is wrong with the following code snippet?


import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class WhatIsWrong implements Runnable {
	
	//shared by threads
	final static Map<String, String> map = new HashMap<String, String>();
	
	
	public static void main(String[] args) throws InterruptedException {
		  ExecutorService pool = Executors.newFixedThreadPool(100);
		    for (int i = 0; i < 100; i++) {
		    	WhatIsWrong wiw = new WhatIsWrong();
		        pool.submit(wiw);

…

10: What is wrong with this code? ConcurrentHashMap & Atomic operations

Q. What output is expected from the following code? What does it actually output?


import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public final class WhatIsWrong implements Runnable {

	private Map<String, Integer> myMap = null;

	public WhatIsWrong(Map<String, Integer> myMap) {
		this.myMap = myMap;
	}

	public static void main(String[] args) throws InterruptedException {

		long start = System.currentTimeMillis();

…

What is wrong with this Java code? Heap Vs Stack, Thread safety & Synchronized

This post covers must know Java Multithreading basics – Heap Vs Stack, Thread-safety & Synchronization. When you have a multithreaded Java application, you need to code in a thread-safe manner. Java interviewers may ask you to detect thread-safety issues as discussed in here.

1.What is wrong with the following code?

A very simple code that should print numbers from 7 to 21.…