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How will you go about improving on the following Java code?

Q1. How will you go about improving on the following code snippet that calculates the new balance based on the current balance, total debits, and total credits? Note: All amounts need to be positive values.

import java.math.BigDecimal;
 
public class CashCalculatorBasic {
 
  public BigDecimal getCalculatedAvailableBalance(BigDecimal currentBalance, BigDecimal totalDebits, 
                                           BigDecimal totalCredits) {
   
    BigDecimal result =  currentBalance
     .subtract(totalDebits)
     .add(totalCredits);
   
    System.out.println("The calculated result is " + result);
   
    return result;
 
  }
 
  public static void main(String[] args) { 
    new CashCalculatorBasic().getCalculatedAvailableBalance(
    new BigDecimal("1250.00"), new BigDecimal("250.00"), new BigDecimal("500.00"));
  }
 
}

import java.math.BigDecimal;

public class CashCalculatorBasic {

public BigDecimal getCalculatedAvailableBalance(BigDecimal currentBalance, BigDecimal totalDebits,

BigDecimal totalCredits) {

BigDecimal result = currentBalance

.subtract(totalDebits)

.add(totalCredits);

System.out.println("The calculated result is " + result);

return result;

}

public static void main(String[] args) {

new CashCalculatorBasic().getCalculatedAvailableBalance(

new BigDecimal("1250.00"), new BigDecimal("250.00"), new BigDecimal("500.00"));

}

A1. Firstly, a good thing about the above code is that it uses the...

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How would you go about designing with UML diagrams

This extends 12 UML Interview Questions & Answers. Q1. How would you go about designing a system as described below? A barn that contains animals such as cows and horses. A farmer milks the cows in the farm, and the animals eat hay that are stored in the barn. …...

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How would you go about.. building an ETL pipeline to handle 3k TPS (i.e transactions per second)

Q1. How would you go about.. building an ETL pipeline to handle 3k TPS? A1. Building a data pipeline (i.e. aka ETL) for 3000 TPS (i.e. Transactions per second), which about ~260 million records per day requires distributed, highly scalable, … Read more ›...

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HTTP Basic Authentication Interview Q&A for Java developers & architects

Q1. What do you understand by the term “HTTP Basic Authentication”? A1. HTTP Basic authentication is the simplest “access controls” technique for web resources like RESTful web service call. It doesn’t require cookies, session identifier and login pages. You need to pass just username and password to the resource. …...

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Injection attack prevention Q&A

Q1. What are the different types of injection security vulnerabilities? A1. SQL Injection, Log Injection, HTTP Response Splitting, XPath Query injection, and LDAP injection. Q2. What is an SQL injection vulnerability, and how will you go about preventing it? A2. … Read more ›...

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Java BDD (Behavior Driven Development) interview Q&A

Q1. What is BDD? A1. BDD is principally an idea about how software development should be managed by both business interests and technical insight. Test-driven development focuses on the developer’s opinion on how parts of the software should work. Behavior-driven development focuses on the users’ opinion on how they want...

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Java exception handling interview questions and answers

Q1. What is the difference between a runtime exception and a checked exception? A1. You must either catch or throw a checked exception. The unchecked exception (aka Runtime exception) does not have to be explicitly handled. Q. So, when to use checked exception, … Read more ›...

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Java ExecutorService with strategy design pattern to execute concurrently & sequentially

Java executor framework for running multi-threaded applications concurrently, sequentially, and with a strategy design pattern to switch between sequential and concurrent execution. 1. Running concurrently

package com.writtentest13;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 
 * Tasks are executed concurrently in a thread pool
 */
public class ThreadExecutorMainCon  {

 private ExecutorService concurrentThreadExecutor;

 public static void main(String[] args) {
  ThreadExecutorMainCon main = new ThreadExecutorMainCon();

  // concurrent executor
  main.concurrentThreadExecutor = Executors.newCachedThreadPool();// or
                  // newFixedThreadPool(3)
  List<Callable<Boolean>> tasks = new ArrayList<Callable<Boolean>>();

  // create dummy tasks
  for (int i = 1; i <= 5; i++) {
   tasks.add(main.createTask(i));
  }

  // submit the tasks to the concurrentThreadExecutor
  try {
      main.concurrentThreadExecutor.invokeAll(tasks);

  } catch (InterruptedException e) {
       e.printStackTrace();
  }

  System.out.println("Completed .........");

 }

 private Callable<Boolean> createTask(final int i) {

  Callable<Boolean> task = new Callable<Boolean>() {

   @Override
   public Boolean call() throws Exception {
      System.out.println("Performing task " + i + " on thread - " + Thread.currentThread().getName());
      return true;
   }

  };

  return task;

 }
}

package com.writtentest13;

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

/**

* Tasks are executed concurrently in a thread pool

public class ThreadExecutorMainCon {

private ExecutorService concurrentThreadExecutor;

public static void main(String[] args) {

ThreadExecutorMainCon main = new ThreadExecutorMainCon();

// concurrent executor

main.concurrentThreadExecutor = Executors.newCachedThreadPool();// or

// newFixedThreadPool(3)

List<Callable<Boolean>> tasks = new ArrayList<Callable<Boolean>>();

// create dummy tasks

for (int i = 1; i <= 5; i++) {

tasks.add(main.createTask(i));

}

// submit the tasks to the concurrentThreadExecutor

try {

main.concurrentThreadExecutor.invokeAll(tasks);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println("Completed .........");

}

private Callable<Boolean> createTask(final int i) {

Callable<Boolean> task = new Callable<Boolean>() {

@Override

public Boolean call() throws Exception {

System.out.println("Performing task " + i + " on thread - " + Thread.currentThread().getName());

return true;

}

};

return task;

}

The output will be

Performing task 1 on thread - pool-1-thread-1
Performing task 5 on thread - pool-1-thread-4
Performing task 4 on thread - pool-1-thread-1
Performing task 3 on thread - pool-1-thread-3
Performing task 2 on thread - pool-1-thread-2
Completed .........

Performing task 1 on thread - pool-1-thread-1

Performing task 5 on thread - pool-1-thread-4

Performing task 4 on thread - pool-1-thread-1

Performing task 3 on thread - pool-1-thread-3

Performing task 2 on thread - pool-1-thread-2

Completed .........

You can see more than 1 thread process 5 tasks concurrently. … Read more ›...

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Java String & Array limitations and OutOfMemoryError

Q1. What is the maximum possible length of a Java String & how much heap space do you need to store the maximum possible String object?
A1. A Java String internally uses a char array (i.e. char[]) and the indices of an array is an integer.

…

javap for debugging and better understanding some Java concepts with 3 practical examples

The javap is a class file dissembler. Here are 3 scenarios you can put javap to use with code examples.

#1 Finding the Java version of the class file within a jar

Extract a class file say “MyJobRunner.class” from a jar file and use javap to find out the version used

bash-3.2$ javap -v MyJobRunner

Compiled from "MyJobRunner.java"
public interface com.myapp.invoke.MyJobRunner
  SourceFile: "MyJobRunner.java"
  RuntimeVisibleAnnotations: length = 0x6
   00 01 00 08 00 00
  minor version: 0
  major version: 51
  Constant pool:
const #1 = class        #9;     //  com/myapp/invoke/MyJobRunner
const #2 = class        #10;    //  java/lang/Object
const #3 = Asciz        executeIlliquidDecsProcess;
const #4 = Asciz        ()V;
const #5 = Asciz        SourceFile;
const #6 = Asciz        MyJobRunner.java;
const #7 = Asciz        RuntimeVisibleAnnotations;
const #8 = Asciz        Lorg/springframework/stereotype/Service;;
const #9 = Asciz        com/myapp/invoke/MyJobRunner;
const #10 = Asciz       java/lang/Object;

{
public abstract void executeIlliquidDecsProcess();

}

bash-3.2$ javap -v MyJobRunner

Compiled from "MyJobRunner.java"

public interface com.myapp.invoke.MyJobRunner

SourceFile: "MyJobRunner.java"

RuntimeVisibleAnnotations: length = 0x6

00 01 00 08 00 00

minor version: 0

major version: 51

Constant pool:

const #1 = class #9; // com/myapp/invoke/MyJobRunner

const #2 = class #10; // java/lang/Object

const #3 = Asciz executeIlliquidDecsProcess;

const #4 = Asciz ()V;

const #5 = Asciz SourceFile;

const #6 = Asciz MyJobRunner.java;

const #7 = Asciz RuntimeVisibleAnnotations;

const #8 = Asciz Lorg/springframework/stereotype/Service;;

const #9 = Asciz com/myapp/invoke/MyJobRunner;

const #10 = Asciz java/lang/Object;

{

public abstract void executeIlliquidDecsProcess();

}

“major version: 51”

…

javap, jps, jmap, and jvisualvm tutorial – analyzing the heap histogram

Q1. Is there anything wrong with the code snippet shown below?

public class SumNumbers {

    public static void main(String[] args) throws InterruptedException{
        Integer sum = 0;
        for (int i = 1000; i < 500000; i++) {
            sum += i;
            Thread.sleep(100);
        }
    }
}

public class SumNumbers {

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

Integer sum = 0;

for (int i = 1000; i < 500000; i++) {

sum += i;

Thread.sleep(100);

}

A1. The above code creates too many “Integer” objects due to auto boxing.

int result = sum.intValue() + i;
sum = Integer.valueOf(result); //creating an Integer object

1 2	int result = sum.intValue() + i; sum = Integer.valueOf(result); //creating an Integer object

Q2. How do you know that the above auto unboxing and boxing code were executed?

…

JConsole for debugging deadlocks in Java

This is another debugging concurrency issues tutorial following on Debugging Java thread-safety, multi-threading, or concurrency issues tutorial. Step 1: Java code that creates a dead lock situation by a) thread-0 holding on to lock1 and waiting for the lock2, … Read more ›...

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JMeter beginner tutorial

This tutorial performance test the RESTFul web service we created ealier as part of the “RESTful Web Service Tutorial with Apache CXF, Maven, and Eclipse” with JMeter. JMeter is an opensource performance testing tool.

Step 1: Download latest release version of Apache JMeter from “http://jmeter.apache.org/download_jmeter.cgi“,

…

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Blog Archives

How will you go about improving on the following Java code?

How would you go about designing with UML diagrams

How would you go about.. building an ETL pipeline to handle 3k TPS (i.e transactions per second)

HTTP Basic Authentication Interview Q&A for Java developers & architects

Injection attack prevention Q&A

Java BDD (Behavior Driven Development) interview Q&A

Java exception handling interview questions and answers

Java ExecutorService with strategy design pattern to execute concurrently & sequentially

Java String & Array limitations and OutOfMemoryError

javap for debugging and better understanding some Java concepts with 3 practical examples

javap, jps, jmap, and jvisualvm tutorial – analyzing the heap histogram

JConsole for debugging deadlocks in Java

JMeter beginner tutorial

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