Integer vs floating point arithmetic - Java Coding Question

I am starting a new series called Java Coding Quiz, in which I'll show you subtle Java concepts hidden in the code. This is an OCAJP or OCPJP style question but focused on teaching subtle details of Java programming language. In today's puzzle, you will learn about one of the key concepts about how floating point and integer arithmetic works in Java. This is a very important concept for any Java developer because Java behaves differently when the same operation is performed by different types of variable but of the same value.

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How to replace a substring in Java?

You can replace a substring using replace() method in Java. The String class provides the overloaded version of the replace() method, but you need to use the replace(CharSequence target, CharSequence replacement). This version of the replace() method replaces each substring of this string (on which you call the replace() method) that matches the literal target sequence with the specified literal replacement sequence. For example, if you call "Effective Java".replace("Effective", "Head First") then it will replace "Effective" with "Head First" in the String "Effective Java". Since String is Immutable in Java, this call will produce a new String "Head First Java".

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Base64 Encoding Decoding Example in Java 8

Until Java 8, there was no standard way to Base64 encode a String in Java or decode a base64 encoded String. Java Programmers either use Apache Commons library and it's Base64 class to encode or decode binary data into base 64 encoding, as shown here, or rely on internal Sun classes e.g. sun.misc.BASE64Encoder and sun.misc.BASE64Decoder(), which were not officially part of JDK and can be removed without notification. Java 8 solves this problem by providing standard support for base64 encoding and decoding by providing a java.util.Base64 class. This class contains methods like getEncoder() and getDecoder() to provide Base64 encoder and decoder to carry out base 64 encoding of String or binary data. In this article, I'll show you some example of how to base64 encode String in Java 8.

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Java Program to print pyramid pattern of stars and numbers

You can print Pyramid pattern of stars or numbers using loops and print methods in Java. There are two print method you need to know, System.out.print() and System.out.println(), the difference between print() and println() is that println adds a new line character at the end i.e. it appends \n automatically. which means next time you write something will begin at the new line. On the other hand, if you use print() then the text is appended to the same line. By using these two methods, you can print any kind of pattern in Java program e.g. pattern involving multiple stars in one line, a pattern involving stars at different lines, pyramid of numbers, a pyramid of stars, inverted pyramid pattern of numbers, stars and alphabets, and so on.

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How to check if String contains another SubString in Java? contains() and indexOf() example

You can use contains(), indexOf() and lastIndexOf() method to check if one String contains another String in Java or not. If a String contains another String then it's known as a substring. The indexOf() method accept a String and return starting position of the string if it exists, otherwise it will return -1. For example "fastfood".indexOf("food") will return 4 but "fastfood".indexOf("Pizza") will return -1. This is the easiest way to test if one String contains another substring or not. The second method is lastIndexOf() which is similar to indexOf() but start the search from the tail, but it will also return -1 if substring not found in the String or the last position of the substring, which could be anything between 0 and length -1.

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How to check if a String is numeric in Java? Use isNumeric() or isNumber()

In day-to-day programming, you often need to check if a given String  is numeric or not. It's also a good interview question but that's a separate topic of discussion. Even though you can use a Regular expression to check if given String is empty or not, as shown here, they are not full proof to handle all kinds of scenarios, which common third party library like Apache commons lang will handle e.g. hexadecimal and octal String. Hence, In Java application, the simplest way to determine if a String is a number or not is by using Apache Commons lang's isNumber() method, which checks whether the String a valid number in Java or not. Valid numbers include hexadecimal marked with the 0x or 0X qualifier, octal numbers, scientific notation and numbers marked with a type qualifier (e.g. 123L). Non-hexadecimal strings beginning with a leading zero are treated as octal values. Thus the string 09 will return false since 9 is not a valid octal value. However, numbers beginning with 0. are treated as decimal.null and empty/blank String will return false.

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How to split String in Java by WhiteSpace or tabs? Example Tutorial

You can split a String by whitespaces or tabs in Java by using the split() method of java.lang.String class. This method accepts a regular expression and you can pass a regex matching with whitespace to split the String where words are separated by spaces. Though this is not as straightforward as it seems, especially if you are not coding in Java regularly. Input String may contain leading and trailing spaces, it may contain multiple white spaces between words and words may also be separated by tabs. Your solution needs to take care of all these conditions if you just wants words and no empty String. In this article, I am going to show you a couple of examples to demonstrate how you can split String in Java by space. By splitting I mean getting individual words as String array or ArrayList of String, whatever you need.

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How to Serialize Object in Java - Serialization Example

Serialization is one of the important but confusing concept in Java. Even experienced Java developer struggle to implement Serialization correctly. The Serialiation mechamism is provided by Java to save and restore state of an object programatically. Java provides two classes Serializable and Externalizable in java.io package to facilitate this process, both are marker interface i.e. an interface without any methods. Serializing an Object in Java means converting into a wire format so that you can either persists its state in a file locally or transfer it to another client via the network, hence it become an extrememly important concept in distributed applications running across several JVMs. There are other features in Java e.g. Remote Method Invocation (RMI) or HttpSession in Servlet API which mandates the participating object should impelment Serializable interface because they may be transffered and saved across the network.

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10 basic differences between Java and Groovy Programming

If you are working in Java, you might have heard about Scala, Groovy, and Closure. Out of these three Groovy seems to be gaining a place in Java projects more rapidly than others. Groovy is a Scripting language but runs on Java virtual machine. Every Java program can run on Groovy platform. As per official Groovy website, "Apache Groovy is a powerful, optionally typed and dynamic language, with static typing and static compilation capabilities, for the Java platform aimed at improving developer productivity thanks to a concise, familiar and easy to learn syntax". I think, they have highlighted the key capabilities of Groovy very well in that sentence. It basically further reduce the burden from Java developer with respect to coding. Now, you can put more focus on business logic and get your work done quickly without wasting time on writing more code.

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Java Comparable Interface and compareTo() Example

Hello, guys, today I am going to talk about one of the fundamental concepts in Java, defining the natural ordering of the objects e.g. lexicographical order for String and numerical order for Number classes e.g. Integer, Double, Float etc. The compareTo() method is defined in the java.lang.Comparable interface. It is used to define the natural ordering of an object e.g. String class override compareTo() to define the lexicographical order for String objects. Integer class override compareTo() to define the numeric ordering of integer objects. Similarly, you can override compareTo() method by implementing Comparable interface to define the natural order on which you want to order your object. For example, an Order should be ordered by order id hence compareTo() must provide logic for that.

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How to calculate GCF and LCM of two numbers in Java? Example

This week's programming exercise is to write a Java program to calculate GCF and LCM of two numbers. The GCF, stands for Greatest common factor and LCM stands for Lowest common multiplier, both are popular mathematical operation and related to each other. The GCF is the largest number which divides both the number without leaving any remainder e.g. if two numbers are 24 and 40 then their GCF is 8 because 8 is the largest number which divides both 24 and 40 perfectly, without leaving any remainder. Similarly, LCM is the lowest number which is perfectly divisible by the two number, for example, if given number is 40 and 24 then their LCM is 120 because this is the lowest number which is perfectly divisible by both 40 and 24.

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Difference in String pool between Java 6 and 7

String pool in Java is a pool of String literals and interned Strings in JVM for efficient use of String object. Since String is immutable in Java, it makes sense to cache and shares them in JVM. The String pool has gone through an important change in Java 7 release when it was relocated from PermGen space to heap space. Till Java 1.6, interned String and literals are stored in the PermGen space of JVM memory, which was a fixed size area for storing class metadata. The biggest issue of having String pool in PermGen is the small and fixed size of PermGen space. In some JVM it ranges from 32M to 96M, which is quite small for a large program. Since String is extensively used in both small and large Java application, Java designers thought String pool is the best way optimize the use of String object in Java.

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Eclipse - How to add/remove external JAR into Java Project's Classpath

There are multiple ways you can add an external JAR into the classpath of a Java project in Eclipse, but all goes via adding them into build path. Many beginner's struggles to add JARs into classpath and we will try to address that problem in this tutorial. You will learn step by step tutorial to add an internal or third party JAR in your application's CLASSPATH in Eclipse Indigo. Since this feature has hardly changed in any Eclipse version, you can follow same steps in Eclipse Kepler, Indigo, and Juno version to add JARs into classpath. Since Eclipse is the most popular Java IDE and used by many companies, it's important for a Java developer to know Eclipse in and out. It will not only help to work better but also to create the better impression among your teammates.

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Printing Largest and Smallest of N numbers without using Array in Java

One of the common programming questions is, how do you find the largest and smallest number in N numbers without using arrays in Java? Can you write a program to solve this problem? Well, it's very similar to the problem we have seen before, find the largest and smallest of 3 integers. You can use the same approach and generalize it for N numbers. All you need to do is start with largest as Integer.MIN_VALUE and smallest number as Integer.MAX_VALUE and loop through N numbers. At each iteration, compare the number with the largest and smallest number, if the current number is larger than largest than its a new largest and if the current number is smaller than smallest than its a new smallest number.

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How to take array input in Java using Scanner - Example

There is no direct way to take array input in Java using Scanner or any other utility, but it's pretty easy to achieve the same by using standard Scanner methods and asking some questions to the user. For example, if you want to take a one-dimensional array of String as input then you can first ask the user about the length of the array and then you can use a for loop to retrieve that many elements from user and store them in an array. You can use the next() to take a String input from the user. Similarly, if you need to take an integer array or double array, you can use nextInt() or nextDouble() method of Scanner class. Some programmer may still stuck and ask, how about taking a two-dimensional array as input? Well isn't that pretty easy by applying some maths?

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10 Examples of Joining String in Java 8 - StringJoiner and String.join()

It's quite common in day to day programming to join Strings e.g. if you have an array or List of String let's say {Sony, Apple, Google} and you want to join them by comma to produce another String "Sony, Apple, Google", there is not an easy way to do it in Java. You need to iterate through array or list and then use a StringBuilder to append a comma after each element and finally to remove the last comma because you don't want a comma after the last element. A JavaScript-like Array.join() method or join() method of Android's TextUtils class is what you need in this situation, but you won't find any of such method on String, StringBuffer, StringBuilder, Arrays, or Collections class until Java 8. Now, you have a class called StringJoiner which allows you to join multiple String by a delimiter.

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Why use Log4j logging vs System.out.println in Java

Printing messages to the console is an integral part of development, testing and debugging a Java program. If you are working on a Server side application, where you can not see what's going on inside the server, your only visibility tool is a log file; without logs, you can not do any debugging or see what's going on inside your application. Though, Java has pretty handy System.out.println() methods to print something on console, which can also be routed to log file but not sufficient for a real-world Java application. If you are running a Java program in Linux or any UNIX based system, Log4j or SLF4j or any other logging framework offers a lot more features, flexibility, and improvement on message quality, which is not possible using the System.out.println() statement.

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Top 5 Books to Learn Concurrent Programming and Multithreading in Java - Best, Must Read

Books are very important to learn something new and despite being in the electronic age, where books have lost some shine to internet and blogs, I still read and recommend them to get a complete and authoritative knowledge on any topic e.g. concurrent programming. In this article, I will share five best books to learn concurrent programming in Java. These books cover basics, starting from how to create and start a thread, parallel programming, concurrency design patterns, an advantage of concurrency and of course pitfalls, issues, and problems introduced due to multithreading. learning concurrent programming is a difficult task, not even in Java but also on other languages like C++ or modern days JVM languages like Groovy, Scala, Closure, and JRuby.

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Minecraft - java.lang.UnsatisfiedLinkError: lwjgl64.dll : Access Denied Solution

You can resolve java.lang.UnsatisfiedLinkError: lwjgl64.dll : Access Denied error in Minecraft by disabling your anti-virus and run. Later you can whitelist the lwjgl64.dll, so that your anti-virus will not block it again. I have talked about java.lang.UnsatisfiedLinkError couple of times on this blog e.g. here and here. But, today I am going to show you one more real life example of java.lang.UnsatisfiedLinkError, which is more interesting. We'll also learn and how to deal with that. This problem is related to Minecraft, one of the most popular game written in Java. Precisely, we are going to solve the "Exception in thread "main" java.lang.UnsatisfiedLinkError: lwjgl64.dll: Access denied" error.

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How to reverse an ArrayList in place in Java - Example

You can reverse an ArrayList in place in Java by using the same algorithm we have used to reverse an array in place in Java. If you have already solved that problem then It's a no-brainer because ArrayList is nothing but a dynamic array, which can resize itself. All elements of an array are stored in the internal array itself. By the way, if you need to reverse an ArrayList then you should be using the Collections.reverse() method provided by Java Collection framework. It's generic method, so you can not only reverse an ArrayList but also Vector, LinkedList, CopyOnWriteArrayList, or any other List implementation. Though, worth noting is that this method internally uses a ListIterator for reversing the list, which might not be as efficient as our algorithm.

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