Which Java SDK Should You Use? | Okta Developer


There has been a lot of confusion lately about Java and its available SDKs (Software Development Kits). You might’ve heard the Java SDK called the JDK. They’re one and the same. Java SE (Standard Edition) is a specification that’s governed by the JCP (Java Community Process). This process decides what goes into (or gets removed from the JDK). Anyone can implement the Java specification. If they pass the TCK (Test Compatibility Kit), they’re considered a viable JDK.

Confusion around the Java SDK started because of two events:

  • Java started releasing new major versions every six months
  • Oracle changed their support model for Java

Here’s a quick summary of Oracle’s changes:

  • Oracle now distributes two JDK builds: Oracle JDK and Oracle OpenJDK
  • Oracle JDK is free for development and testing, but you have to pay for it if you use it in production
  • Oracle’s OpenJDK is free for any environment

To make matters more contentious, Oracle will end public updates for Java 8 this month! This isn’t out of the ordinary, it regularly does this for major Java versions after five years of public availability. Related: public updates for Java 11 will end this March when Java 12 is released.

This largely has to do with support contracts. I don’t know about you, but I’ve never paid for a Java support contract in my career. Granted, I’ve spent most of my developing days as an independent consultant. I’m willing to bet that most of you haven’t paid for Java support either. My guess is the people who pay for Java support are in charge of companies that built their business on Java and can’t migrate to the latest version. They need support and security fixes for older versions because they can’t upgrade.

Java Is Still Free

When Oracle changed its support model for Java, there was a low roar in the community that Java was no longer free. To help clarify things, the Java Champions group created an open letter clarifying the available support options. You can read more in InfoQ’s Java Community Leaders Clarify Platform Support Options: "Java Is Still Free".

Java SDK Options

Currently, the only source code for the JDK is in the Open JDK project. You can check out the source code for OpenJDK and build it yourself if you like. However, it’s not considered "Java SE compatible" unless it passes the TCK. Also, you cannot call it "Java SE" without getting a license from Oracle.

There are many Java SDK options besides Oracle’s. Let’s take a look at the main ones and when you might want to use them. I’ve listed them below in alphabetical order.

Hat tip to Stephen Colebourne and his Time to look beyond Oracle’s JDK blog post for much of this information.


AdoptOpenJDK is a community and code that builds free OpenJDK binaries. They’re published to adoptopenjdk.net. Binaries are published for five years after the version’s initial release. Builds are available for OpenJ9 (IBM’s JVM) and HotSpot.

What is OpenJ9? According to the AdoptOpenJDK website, OpenJ9 is designed for low memory usage and fast start-up time.

AdoptOpenJDK builds are not tested with the TCK due to a disagreement with Oracle. They do test with a suite of functional, integration, and performance tests. They also test popular framework libraries, languages, and applications.

Amazon Corretto

Amazon is the new vendor on the block that’s offering builds of OpenJDK at aws.amazon.com/corretto. Amazon Corretto 8 (based on Java 8) is in preview; there is no Java 11 build available. Corretto is unique in that it has no-cost long-term support from Amazon. It’s builds have passed the TCK. Java 8 support is currently slated to run through June 2023.

Amazon also offers paid support for Corretto. All AWS instances that run Java use Corretto by default.

Azul Zulu

Azul builds and publishes Zulu at azul.com/downloads/zulu. It’s an OpenJDK build that’s passed the TCK and is fully compliant with the Java SE standard. Zulu Enterprise is Azul’s commercial offering with paid support. It provides long-term support for eight years after the version’s initial release.

Microsoft’s Azure platform uses Zulu for its Java support.

Oracle’s OpenJDK

Oracle builds and publishes OpenJDK builds at jdk.java.net. Binaries are only published for the first six months after a major release. The branded, commercial version (that can’t be used in production without paying Oracle) is available at oracle.com/technetwork/java/javase/downloads.

jdk.java.net is where Oracle’s OpenJDK builds are published for download, openjdk.java.net is the OpenJDK project itself.

Red Hat

Red Hat distributes OpenJDK builds via Red Hat Enterprise Linux, a commercial product. It also has an IcedTea project that builds OpenJDK and adds some features. However, it doesn’t seem to be very active (there’s no Java 11 support) and you hardly hear about it anymore.

Which JDK Should You Use?

The JDK I use is largely determined by the tool I use to install Java. I used to download and install Java manually. When I did that, I used Oracle’s JDK. These days, I use SDKMAN!, a command line tool that installs and manages versions for me. SDKMAN determines the distributions I use today.

SDKMAN is all about convenience. The project aims to make it as easy as possible for you to install Java. If you run sdk install java, it installs Azul Zulu 8. This is because java.net does not provide an OpenJDK distro for any version less than 9.0.

To see the versions available from SDKMAN, you can run sdk list java:

Available Java Versions
 13.ea.02-open       1.0.0-rc-9-grl
 12.ea.26-open       1.0.0-rc-8-grl
  • 11.ea.26-open
  • 11.0.1-open
  • 11.0.0-open
    > + 8.0.181-zulu


    • local version
    • installed
      > - currently in use

      You can see from this list that I have Azul Zulu 8 as my current JDK, and I also have OpenJDK 11 (11.0.1-open) installed. Who built the OpenJDK 11 version I’m using? I assume it’s the one from jdk.java.net, but I don’t really care. It works, and I love using it! However, I can only use Java 11 when working on Spring Boot 2.1 projects, so I don’t get to use it every day. I do a lot of maintenance on Spring Boot examples, and JHipster still uses Spring Boot 2.0. The good news is it’ll be upgrading to Spring Boot 2.1 very soon!

      Long story short: Use whichever JDK SDKMAN gives you, and move on!

      What do other Java Experts Think?

      I figured it’d be fun to interview some of the Java experts here at Okta and get their thoughts on which JDK to use.

      • Les Hazlewood is a senior architect at Okta. Before Okta, he was Stormpath’s co-founder and CTO. He’s also the founder and lead developer of the Apache Shiro and JJWT projects.
      • Brian Demers is the lead Java SDK developer at Okta and a major contributor to Apache Shiro, among other open source projects. By "lead Java SDK developer", I mean that he develops and maintains the Okta Java Management SDK and the Okta Spring Boot starter.
      • Micah Silverman is a technical instructor at Okta. Before Okta, he was one of Stormpath’s lead Java SDK developers.

      First, can you provide everyone with some background on your experience with Java?

      Brian Demers: I’ve been using Java since 1.3 the early '00s and remember the days when XML the solution to all problems. My career seems to have lead down the path of build tools and web security. This has also forced me to support using JVMs on a variety of systems. I’m also passionate about the OSS world and contributed projects like Sonatype’s Nexus, Apache Maven, and Apache Shiro.

      Micah Silverman: I’ve been using Java since its initial release in 1995 (AWT anyone?). The first thing I ever wrote was an applet for the SyFy Channel (SciFi back then) that was an online Ouija board where the answers you got were from a dictionary of SF, horror and fantasy terms. I took a sharp turn from there into large banking and insurance companies, all of which became Java shops fast. I taught Enterprise Java at New York University as an adjunct professor and got to co-author a book on EJB 3.0.

      What is your favorite thing about Java?

      Brian Demers: The community, It’s very easy to find existing quality projects from one of the bigger foundations like the Apache Software Foundation or Eclipse Foundation, as well as finding any number of instructional blog posts.

      Micah Silverman: I love the way the language and community continue to adapt and evolve over the years. There seems to be an "Is Java dead?" post every year or two since its release. It’s remained a relevant and hugely adopted language (and put my daughter through college) because it hasn’t grown stale or fixed. There was a time when Java was first released for Linux that it only supported "green threads". These were virtualized threads and the performance was terrible. There were lots of "Java will die" articles during this period. But eventually, the builds supported native threads, the binaries became leaner and faster and now Java is on billions of devices around the world. Even with the bumpy road that it’s been with Sun and now Oracle’s stewardship, the open nature of the language and JVM specification has kept it growing.

      What Java SDK are you using right now?

      Brian Demers: Currently Corretto:

      $ java -version
      openjdk version "1.8.0_192"
      OpenJDK Runtime Environment (build 1.8.0_192-amazon-corretto-preview-b12)
      OpenJDK 64-Bit Server VM (build 25.192-b12, mixed mode)

      Recently, I was running GraalVM more or less by accident, I installed it to play around with the "native-image" options, and a couple weeks later, realized it was still on my path. Creating a single binary from a Java project has me excited for the possibility of creating easy to install CLI tools.

      I’ve been burned by OpenJDK in the past, so I was pretty hesitant to switch, but I haven’t run into any problems yet.

      Micah Silverman: Currently Oracle (I use jenv to manage versions):

      $ jenv versions
  • (set by /Users/micahsilverman/.jenv/version)

    I also have OpenJDK 11 installed.

    What Java SDK do you recommend for development? For production?

    Demers: This is tricky one, many of us are still going to be supporting a minimum version of Java 8 for a while. Generally, I’d say for development, use what you are using in production, but for things like library development, it’s definitely time to move to an OpenJDK distro. For production, I suggest starting with what is readily available on your platform (Amazon, Red Hat) and switch later to a different distro later if you need to.

    Micah Silverman: For me today, it’s squarely Java 8 in development and production. That’s because the people I support are primarily using Java 8. That said, I set a goal for myself to update my relevant blog posts and examples as well as the production code I’ve written for my team to Java 11 this year. We’ll see how that goes. I was pissed that while the incorporation of Jigsaw with Java 9 and above is awesome, it essentially broke existing code immediately. I would’ve liked to have seen a "compatibility mode" or some such to ease the transition. But, the route of "pulling the band-aid" is not terrible either. I just haven’t gotten there yet.

    I asked Les Hazlewood about OpenJDK versus Oracle. Here’s what he had to say:

    "The only time the OpenJDK builds have been a big pain for me is that they were woefully behind the Oracle JDK’s implementation for TLS cipher suites and TLS version (1.1, 1.2) implementations. However, the open-source projects I work on have a pretty large exposure to diverse crypto algorithms and reverse-proxy types of workloads which leverage these things pretty deeply, so that very likely may not represent the types of issues others might encounter with standard web apps or microservices when trying OpenJDK. Especially if OpenJDK 11 and later are supposedly more aligned with the Oracle JDK releases.

    That said, I am fairly nervous about the ability to receive timely bug fixes and point revision patches over OpenJDK’s lifetime. With the new Java versioning strategy, the only way to obtain those patches long term without paying would be to upgrade as soon as possible to the latest stable releases (11, then 12, then 13) as soon as they’re released. That can potentially significantly increase build/ci/test compatibility burden. However, given that these releases are time-based – and not as much feature-based – the amount of conflicts you might see from version upgrades after getting to the 11 baseline I would expect would be much, much fewer than what most people experienced going from version 7 to 8. So this could be attainable but definitely increases testing and rollout workload for software engineering and operations teams. Not fun but doable.

    I also have had some exposure with the Azul guys in the past. It was a while ago, but I was quite impressed with their garbage collectors that came out long before JDK 8’s dynamic collector. I think Azul customers haven’t had to deal with PermGen Space Exceptions for almost a decade now, if not longer. Their engineering team at the time I engaged with them was extraordinarily smart, and assuming they’re still staffed with such folks, I personally would feel confident using their JDK implementations in production after suitable testing.

    Given that people can’t use JDK 11 or later in production without paying, my particular take on a pragmatic approach for an engineering team would be:

    • Upgrade to OpenJDK 11 as soon as possible. Oracle JDK 9 and 10 are not Long Term Support candidates and 11 is. Regardless of which JVM distribution you use, this will give you the most options with respect to time: if you decide to stick with Oracle, that will give you the longest/safest platform to build and deploy against due to 11’s Long Term support, albeit at a monetary cost.
    • Enable Zulu (Azul’s OpenJDK distribution name) JDKs (JDK 11 APIs) in your CI environment as soon as possible. These JDKs are free to use in dev and production without paying a license fee. You can decide to pay for 8x5 or 24x7 support if/when it becomes important enough for you to do so. At least testing this distribution this would give you an idea of what you’re up against, and it might just go more smoothly than expected. Assuming smooth testing, I’d be completely comfortable using Zulu in production."

    Install Java Today!

    There you have it. A plethora of opinions about which JDK you should use in development and production. In reality, you might not have an option of what distribution you use in production. If you’re using a cloud provider, they might dictate the distribution and version for you.

Java to C# – C# to Java

Java to C# – C# to Java

In this post, we bring you a much needed Rosetta Stone — an explanatory bridge between these two technologies

Originally published by Andy Macdonald at https://medium.com
Java and C# are incredibly similar. Both languages are somewhat derived from C++ and from similar first principles.

Java was developed in 1995 to create a language with a simpler programming model than C++ while still preserving some of the same syntax of the language to facilitate developers transitioning to it.

C# was developed in 2000 by Microsoft as part of its .NET drive in order to develop a language and set of technologies that could address some of the perceived weaknesses of the C++ language. It was also developed with quite heavy “inspiration” from the Java language.

Despite the similarities between the languages and sharing some common ground, transitioning from one technology to the other for a developer well-practised in one technology can be quite tricky.

Innovation happens best when there is collaboration between people of different mindsets — yet users of C# and Java can be somewhat tribalistic.

To that end, I thought it would be useful to put together a sort of guide to help people thinking about or starting to transition between these two technologies. It would also be nice in some way to facilitate a bit more collaboration between these two worlds — hopefully to do my bit to reduce the needless gulf that exists between them.

Some of the similarities right off the bat:

Java is a language that runs in a virtual machine environment (JVM) and runs bytecode that the Java compiler generates.

For C#, the situation is similar. It is a language that runs on the .NET framework and the CLR runtime. It uses a similar intermediary language to Java bytecode called MSIL which gets run via CLR.

Naming and Conventions

Some of the key and most immediately obvious differences in nomenclature, syntax, and conventions are:

  • “Projects” (Java) — “Solutions” (C#)
  • In Java, methods use lowerCamelCase (bar.doAThing()), whilst in C# public methods use PascalCase (bar.DoAThing())
  • In C#, interfaces are always prefixed with an I, as in IUserService<T>, instead of UserService<T>** **in Java
  • In Java, a string is a String** **— in C# a string is a string
  • “POJO” (Java) — “POCO” (C#)
  • Packages (Java) — Namespaces (C#)

Package (Java)

package dev.andymacdonald;

// Code goes here

Namespace (C#)

namespace Dev.AndyMacdonald 
  // Code goes here


**Java has <strong>final</strong> variables — C# has **<strong>readonly</strong>

A key difference here is that Java final variables can be assigned once anywhere in the class, whereas C#’s readonly variables can only be assigned in the constructor.

C# has <strong>out</strong> and <strong>ref</strong> parameters to allow passing arguments by reference — Java doesn’t

It can manipulate objects and variables by reference, but in a method, these arguments are passed by a value. With C#, we can override this behaviour with the out and ref keywords.

Annotations (Java) — attributes (C#)

These are basically equivalent concepts and just differ in actual syntax. Both annotations and attributes can be accessed via each language’s respective Reflection API implementation.

Java annotation:

private String fullName;

C# attribute:

private string fullName;

Getters and setters or Project Lombok (Java) — C# properties

C# really overtakes Java here with its built-in properties* *feature. In the standard JDK, there isn’t an equivalent to this, and instead, in Java, getters and setters must be written for each field requiring an accessor.

These are often just generated by the developer with their IDE as a cheat … still a bit tedious, though.

Java getters and setters:

public class Element 
  private String symbol;   
  private String name;   
  private int atomicNumber;
  public int getAtomicNumber() 
    return this.atomicNumber;
  public String getSymbol() 
    return this.symbol;
  public String getName() 
    return this.name; 
  public void setAtomicNumber(int atomicNumber) 
    this.atomicNumber = atomicNumber;
  public void setName(String name) 
    this.name = name;
  public void setSymbol(String symbol) 
    this.symbol = symbol;

Many Java projects incorporate Project Lombok, which adds getters, setters, equals, and hash code (plus other useful boilerplates) at compile time.

Project Lombok — not part of the standard library:

@Getter @Setter
public class Element 
  private String symbol;   
  private String name;   
  private int atomicNumber;

C# built-in properties feature:

public class Element 

  public string Symbol { get; set; }     
  public string Name { get; set; }     
  public int AtomicNumber { get; set; }


Java for each loop:

List<Integer> fibNumbers = Arrays.asList(0, 1, 1, 2, 3, 5, 8, 13);
int count = 0;
for (int element: fibNumbers)
    System.out.println(String.format("Element #%s: %s", count, element));
System.out.println(String.format("Number of elements: %s", count));

C# for each loop:

var fibNumbers = new List<int> { 0, 1, 1, 2, 3, 5, 8, 13 };
int count = 0;
foreach (int element in fibNumbers)
    Console.WriteLine($"Element #{count}: {element}");
Console.WriteLine($"Number of elements: {count}");

Implementing interfaces/inheritance

Inheritance and implementing interfaces isn’t drastically different between the two languages. Java uses the extends or implements keywords; C# uses C++ syntax (derivation declaration) B : A for defining inheritance.

Defining and implementing an interface with methods in Java:

package dev.andymacdonald;

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

interface Fish
   void swim();

class Salmon implements Fish

   public void swim()

class Cod implements Fish
   public void swim()

public class Program
   public static void main()
      List<Fish> fishes = new ArrayList<>();
      fishes.add(new Salmon());
      fishes.add(new Cod());

      for (Fish fish : fishes)

Defining and implementing an interface with methods in C#:

using System;
using System.Collections.Generic;

namespace Dev.AndyMacdonald 
    interface Fish
        void Swim();
    class Salmon : Fish
        public void Swim()
    class Cod : Fish
        public void Swim()
    class Program
        static void Main()
            List<Fish> fishes = new List<Fish>();
            fishes.Add(new Salmon());
            fishes.Add(new Cod());
            foreach (Fish fish in fishes)


Quite simply, Java just doesn’t do pointers, whereas in C# it is possible to do pointer arithmetic and manipulation.

 unsafe {
  int a = 25;
  int * ptr = &a;
  Console.WriteLine($"Value of pointer is {*ptr}");


Visual Studio

C# developers traditionally and typically use the Visual Studio IDE. This is a situation borne out of the origins of .NET being a closed-source technology. Microsoft developed Visual Studio** **to be a one-stop shop for all things .NET.

Java went down a different route, offering much more developer choice in tooling from the outset. That’s why there’s a much greater range of IDEs for Java development (e.g., IntelliJ, Eclipse, NetBeans). Gradually the landscape for .NET developers has shifted, and more IDEs and developer choice has been offered over the years.

IntelliJ (Java) — Rider (C#)

Users of JetBrains IDEs will find the transition from one IDE to another very smooth if they choose to make a switch to the respective JetBrains IDE in the technology they are targeting. Keyboard shortcuts, IDE layout, and even some plugins are equivalent or comparable — virtually the same IDE.

Dependency Management

Maven (Java) — NuGet and dotnet CLI (C#)

Maven is a tool responsible for dependency management and the life cycle of the building of typically Java and JVM applications. That said, it is pretty flexible, has 1000s of plugins, and can be used to build applications of other languages, such as PHP and JavaScript.

The configurable unit of maven is a pom.xml file that every maven project has. For a project’s submodules, it is possible to have a pom file per submodule which inherits from a parent. Maven uses a remote server or repository of some kind to host and retrieve packages.

Maven pom.xml file (Java):

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">




At the simplest level, you can test and build a Maven project with the following command:

mvn clean install

And create a package with this:

mvn clean package

And finally, deploy a package like this:

mvn clean deploy

NuGet fulfills a similar, though not identical role in .NET to Maven. NuGet can use a few different configuration files but commonly uses .csproj*. *As with Maven, NuGet uses a server/repository that can host packages.

NuGet .csproj file:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <Compile Include="helloworld.cs" />
    <PackageReference Include="MyDependency" version="1.0.0" />
  <Target Name="Build">
    <MakeDir Directories="$(OutputPath)" Condition="!Exists('$(OutputPath)')" />
    <Csc Sources="@(Compile)" OutputAssembly="$(OutputPath)$(AssemblyName).exe" />

NuGet’s primary role is package management, construction, and deployment. Java developers will notice that it doesn’t really have the same concept of build phases as Maven does. Additionally, .NET developers don’t tend to edit their build files manually as Java developers do with pom.xml files, preferring to manipulate them in their IDE instead.

Packages can be built, packaged, and deployed to NuGet with the following nuget commands:

nuget spec
nuget pack {nuspec file}
nuget push {package file} {apikey} -Source {host url}

If you want to run the tests for your .NET application, you can run the following dotnet CLI command:

dotnet test

The dotnet CLI can also be used as a wrapper around nuget commands.

Application Servers

Apache Tomcat (Java) — IIS (ASP.NET)

Tomcat is an open-source web server and servlet container from the Apache Foundation. Though there are many other application servers used widely in Java, it is a pretty common choice for most enterprise-software companies. It works across pretty much every operating system (e.g., Windows, Unix, Linux, and Mac OS).

.NET projects are typically deployed on IIS, a web server that only runs on Windows. While its portability is limited, it’s a pretty popular choice for Windows developers because of its ease of use and simplicity while still offering some advanced configuration options.

… But Wait!

For .NET Core web applications, you can package them to run as standalone web applications — allowing you to run them like this:

dotnet <app_assembly>.dll

In the same way you can run a Java Spring Boot web*** ***application (which has a self-contained Tomcat server):

java -jar <my-application>.jar

And visit your shiny new web app like this:


Libraries and Frameworks

Spring Framework (Java) — ASP.NET (C#)

The Spring Framework is a framework and IoC container for Java. In short, the Spring framework is responsible for instantiating objects (beans) and managing the life cycle of these beans in memory.

Create an ApplicationContext* *(similar to the concept of a Startup in ASP.NET). This example uses Spring Boot:

public class HumanApplication
   public static void main(String[] args) 
      SpringApplication.run(HumanApplication.class, args);

Create an interface:

public interface Organ<T>
   void function();

Implement the Organ<T> interface:

public class Heart implements Organ<Heart>
    public Heart() {}
    public void function() 

Constructor injection of Organ dependencies list into a Human service:

public class Human 
    private static final int MAX_SECONDS_OF_LIFE = 3000;
    private List<Organ> organs;
    public Human(List<Organ> organs) 
        this.organs = organs;
    public void live() 
        for (int i = 0; i < MAX_SECONDS_OF_LIFE; i++) 
            organs.forEach(organ -> organ.function());

Run the application …

It’s aliiiiiiive:


Spring also ships with a handy suite of modules and packages.

In the core Spring packages, and in the convention-over-configuration extension to the framework, Spring Boot, useful combinations of existing and bespoke technologies are provided for developers wanting access to common libraries to kickstart a project with all that they may need, rather than having to write or track down these utilities themselves:

  • RestTemplate (spring-web — for constructing REST and HTTP requests)
  • JdbcTemplate (spring-data — for constructing JDBC queries and statements)
  • Spring Security (for creating and managing application security models)
  • ObjectMapper (spring-core — useful utility for mapping POJOs from Jackson)
  • etc.

ASP.NET fulfills a similar role in the world of C#, providing IoC functionality, commonly used technologies, and utilities in a single framework. However, ASP.NET generally only provides IoC functionality for web applications, whereas the Spring Framework provides this for any application type.

In terms of dependency inversion, it is possible to do very similar things in ASP.NET as in Spring.

As before, define the needed interface and concrete implementation:

public interface Organ<T>
   void Function();
public class Heart : Organ<Heart>
    public Heart() {}
    public void Function() 

Invoke functions of injected dependencies:

public class Human

   private List<IOrgan> _organs;
   public Human(List<IOrgan> organs)
      _organs = organs;
   public void Live()
      organs.ForEach(organ =>

Define a Startup and register services:

public class Startup  
  public void ConfigureServices(IServiceCollection services)
    services.AddTransient<IList<IOrgan>>(p => p.GetServices<IOrgan>().ToList());

ASP.NET also fulfills the role of providing many useful libraries and utilities to accelerate development of your project.

Streams (Java) — LINQ (C#)

Both Java and C# have mechanisms to simplify the reduction of data sets — Streams and LINQ.

There are some differences and gaps between the two technologies but if you have familiarity with one, you’ll be able to get up and running fairly quickly with the other.

Java Streams:

List<Student> studentList = Arrays.asList( 
    new Student(1, "John", 18, 1),
    new Student(2, "Steve", 21, 1),
List<String> studentNames = studentList.stream()
    .filter(s -> s.getAge() > 18)
    .filter(s -> s.getStandardID() > 0)
    .map(s -> s.getName()).collect(Collectors.toList());
studentNames.forEach(name -> System.out.println(name));

LINQ Query (C#):

IList<Student> studentList = new List<Student>() { 
    new Student() { StudentID = 1, StudentName = "John", Age = 18, StandardID = 1 } ,
    new Student() { StudentID = 2, StudentName = "Steve",  Age = 21, StandardID = 1 }
var studentNames = studentList.Where(s => s.Age > 18)
                        .Where(st => st.StandardID > 0)
                        .Select(s => s.StudentName);
foreach(var name in studentNames) {   

Apache Commons (Java) — CommonLibrary.NET (C#)

Apache Commons*** ***provides Java developers with a collection of several independently released, useful components and utilities for the purposes of accelerating development.

If you’re in need of a utility to work with ZIP files or a set of utilities for working with mathematical expressions and formulae, then Apache Commons has you covered.

In a similar way, CommonLibrary.NET covers these bases too — there are some key differences in naming of some components and modules, but for the most part, they are pretty much equivalent in their purpose.

That said, unlike Apache Commons, CommonLibrary.NET is quite old and isn’t very commonly used in projects anymore. If you’re after a continuously updated, curated list of libraries for each respective technology, I highly recommend these two lists:



Testing Libraries

JUnit (Java) — NUnit (C#)

Java’s ever-dependable JUnit library has a direct equivalent in C#.

NUnit has almost equivalent functionality to JUnit and is a popular choice for C# developers.


public void complexNumberTest()
    ComplexNumber result = someCalculation();
    Assert.assertEquals("Real", 5.2, result.getRealPart());
    Assert.assertEquals("Imaginary" 3.9, result.getImaginaryPart());


public void ComplexNumberTest()
    ComplexNumber result = SomeCalculation();
    Assert.Multiple(() =>
        Assert.AreEqual(5.2, result.RealPart, "Real");
        Assert.AreEqual(3.9, result.ImaginaryPart, "Imaginary");

(Rumour has it NUnit started life as the JUnit source code modified to run in C#.)

Mockito (Java) — Moq (C#)

As with JUnit and NUnit, comparable functionality exists between Java’s Mockito and C#’s Moq library.


Foo mockFoo = mock(Foo.class);


var mock = new Mock<IFoo>();
mock.Setup(foo => foo.DoSomething("ping")).Returns(true);

That’s It

Thanks for Reading!

I obviously couldn’t fit every difference, similarity, and detail in this article —* *it’s already far too long.

I hope at least I’ve covered enough ground to make you feel confident to make a switch and see how the other half lives.

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Further reading

Java Tutorial for Absolute Beginners

100+ Java Interview Questions and Answers In 2019

Python vs Java: Understand Object Oriented Programming

Angular 7 + Spring Boot CRUD Example

Build a Simple CRUD App with Spring Boot and Vue.js

Java String – String Functions In Java With Examples

Java String – String Functions In Java With Examples

In this post, we will be discussing about a new concept, Java String. String is a sequence of characters. But in Java, a string is an object that represents a sequence of characters. The java.lang.String class is used to create string object.

Originally published by Aayushi Johari at https://www.edureka.co
There are two ways to create a String object:
By string literal : Java String literal is created by using double quotes. For Example: String s=“Welcome”; By new keyword : Java String is created by using a keyword “new”. For example: String s=new String(“Welcome”); It creates two objects (in String pool and in heap) and one reference variable where the variable ‘s’ will refer to the object in the heap.
Now, let us understand the concept of Java String pool.

**Java String Pool: **Java String pool refers to collection of Strings which are stored in heap memory. In this, whenever a new object is created, String pool first checks whether the object is already present in the pool or not. If it is present, then same reference is returned to the variable else new object will be created in the String pool and the respective reference will be returned. Refer to the diagrammatic representation for better understanding:

In the above image, two Strings are created using literal i.e “Apple” and “Mango”. Now, when third String is created with the value “Apple”, instead of creating a new object, the already present object reference is returned. That’s the reason Java String pool came into the picture.

Before we go ahead, One key point I would like to add that unlike other data types in Java, Strings are immutable. By immutable, we mean that Strings are constant, their values cannot be changed after they are created. Because String objects are immutable, they can be shared. For example:

   String str =”abc”;

is equivalent to:

char data[] = {‘a’, ‘b’, ‘c’};
     String str = new String(data);

Let us now look at some of the inbuilt methods in String class.

Java String Methods

Java String length(): The Java String length() method tells the length of the string. It returns count of total number of characters present in the String. For example:

public class Example{
public static void main(String args[]{
String s1="hello";
String s2="whatsup";
System.out.println("string length is: "+s1.length()); 
System.out.println("string length is: "+s2.length());

Here, String length() function will return the length 5 for s1 and 7 for s2 respectively.
Java String compareTo(): The Java String compareTo() method compares the given string with current string. It is a method of* ‘Comparable’* interface which is implemented by String class. Don’t worry, we will be learning about String interfaces later. It either returns positive number, negative number or 0. For example:

public class CompareToExample{
public static void main(String args[]){
String s1="hello";
String s2="hello";
String s3="hemlo";
String s4="flag";
System.out.println(s1.compareTo(s2)); // 0 because both are equal
System.out.println(s1.compareTo(s3)); //-1 because "l" is only one time lower than "m"
System.out.println(s1.compareTo(s4)); // 2 because "h" is 2 times greater than "f"

This program shows the comparison between the various string. It is noticed that

if s1 > s2, it returns a positive number

if s1 < s2, it returns a negative number

if s1 == s2, it returns 0
**Java String concat() : **The Java String concat() method combines a specific string at the end of another string and ultimately returns a combined string. It is like appending another string. For example:

public class ConcatExample{
public static void main(String args[]){
String s1="hello";
s1=s1.concat("how are you");

The above code returns “hellohow are you”.
Java String IsEmpty() : This method checks whether the String contains anything or not. If the java String is Empty, it returns true else false. For example:

public class IsEmptyExample{
public static void main(String args[]){
String s1="";
String s2="hello";
System.out.println(s1.isEmpty());      // true
System.out.println(s2.isEmpty());      // false

  • Java String Trim() : The java string trim() method removes the leading and trailing spaces. It checks the unicode value of space character (‘u0020’) before and after the string. If it exists, then removes the spaces and return the omitted string. For example:
public class StringTrimExample{ 
public static void main(String args[]){ 
String s1="  hello   "; 
System.out.println(s1+"how are you");        // without trim() 
System.out.println(s1.trim()+"how are you"); // with trim() 

In the above code, the first print statement will print “hello how are you” while the second statement will print “hellohow are you” using the trim() function.

  • Java String toLowerCase() : The java string toLowerCase() method converts all the characters of the String to lower case. For example:
public class StringLowerExample{
public static void main(String args[]){
String s1="HELLO HOW Are You?”;
String s1lower=s1.toLowerCase();

The above code will return “hello how are you”.

  • Java String toUpper() : The Java String toUpperCase() method converts all the characters of the String to upper case. For example:
public class StringUpperExample{ 
public static void main(String args[]){ 
String s1="hello how are you"; 
String s1upper=s1.toUpperCase(); 

The above code will return “HELLO HOW ARE YOU”.
Java String ValueOf(): This method converts different types of values into string.Using this method, you can convert int to string, long to string, Boolean to string, character to string, float to string, double to string, object to string and char array to string. The signature or syntax of string valueOf() method is given below: public static String valueOf(boolean b) public static String valueOf(char c) public static String valueOf(char[] c) public static String valueOf(int i) public static String valueOf(long l) public static String valueOf(float f) public static String valueOf(double d) public static String valueOf(Object o)
Let’s understand this with a programmatic example:

public class StringValueOfExample{
public static void main(String args[]){
int value=20;
String s1=String.valueOf(value);
System.out.println(s1+17);       //concatenating string with 10

In the above code, it concatenates the Java String and gives the output – 2017.
Java String replace(): The Java String replace() method returns a string, replacing all the old characters or CharSequence to new characters. There are 2 ways to replace methods in a Java String.

public class ReplaceExample1{
public static void main(String args[]){
String s1="hello how are you";
String replaceString=s1.replace('h','t');
System.out.println(replaceString); }}

In the above code, it will replace all the occurrences of ‘h’ to ‘t’. Output to the above code will be “tello tow are you”. Let’s see the another type of using replace method in java string:

**Java String replace(CharSequence target, CharSequence replacement) method **:

public class ReplaceExample2{
public static void main(String args[]){
String s1="Hey, welcome to Edureka";
String replaceString=s1.replace("Edureka","Brainforce");

In the above code, it will replace all occurrences of “Edureka” to “Brainforce”. Therefore, the output would be “ Hey, welcome to Brainforce”.
Java String contains() :The java string contains() method searches the sequence of characters in the string. If the sequences of characters are found, then it returns true otherwise returns false. For example:

class ContainsExample{
public static void main(String args[]){
String name=" hello how are you doing";
System.out.println(name.contains("how are you"));  // returns true
System.out.println(name.contains("hello"));        // returns true 
System.out.println(name.contains("fine"));         // returns false 

In the above code, the first two statements will return true as it matches the String whereas the second print statement will return false because the characters are not present in the string.
Java String equals() : The Java String equals() method compares the two given strings on the basis of content of the string i.e Java String representation. If all the characters are matched, it returns true else it will return false. For example:

public class EqualsExample{
public static void main(String args[]){
String s1="hello";
String s2="hello";
String s3="hi";
System.out.println(s1.equalsIgnoreCase(s2));   // returns true
System.out.println(s1.equalsIgnoreCase(s3));   // returns false

  • **JavaString equalsIgnoreCase(): **This method compares two string on the basis of content but it does not check the case like equals() method. In this method, if the characters match, it returns true else false. For example:
public class EqualsIgnoreCaseExample{
public static void main(String args[]){
String s1="hello";
String s2="HELLO";
String s3="hi";
System.out.println(s1.equalsIgnoreCase(s2));   // returns true
System.out.println(s1.equalsIgnoreCase(s3));   // returns false

In the above code, the first statement will return true because the content is same irrespective of the case. Then, in the second print statement will return false as the content doesn’t match in the respective strings.
**Java String toCharArray(): **This method converts the string into a character array i.e first it will calculate the length of the given Java String including spaces and then create an array of char type with the same content. For example:

public static void main(String args[]){
String s1="Welcome to Edureka";
char[] ch=s1.toCharArray();
for(int i=0;i<ch.length;i++){

The above code will return “Welcome to Edureka”.
Java StringGetBytes() : The Java string getBytes() method returns the sequence of bytes or you can say the byte array of the string. For example:

public class StringGetBytesExample {
public static void main(String args[]){
String s1="ABC";
byte[] b=s1.getBytes();
for(int i=0;i<b.length;i++){

In the above code, it will return the value 65,66,67.
Java String IsEmpty() : This method checks whether the String is empty or not. If the length of the String is 0, it returns true else false. For example:

public class IsEmptyExample{
public static void main(String args[]) {
String s1="";
String s2="hello";
System.out.prinltn(s1.isEmpty());     // returns true
System.out.prinltn(s2.isEmpty());     // returns false

In the above code, the first print statement will return true as it does not contain anything while the second print statement will return false.
Java String endsWith() : The Java String endsWith() method checks if this string ends with the given suffix. If it returns with the given suffix, it will return true else returns false. For example:

public class EndsWithExample{
public static void main(String args[]) {
String s1="hello how are you”;
System.out.println(s1.endsWith("u"));       // returns true
System.out.println(s1.endsWith("you"));     // returns true  
System.out.println(s1.endsWith("how"));     // returns false

This is not the end. There are more Java String methods that will help you make your code simpler.

Moving on, Java String class implements three interfaces, namely – Serializable, Comparable and CharSequence.

Since, Java String is immutable and final, so a new String is created whenever we do String manipulation. As String manipulations are resource consuming, Java provides two utility classes: StringBuffer and StringBuilder.

Let us understand the difference between these two utility classes:
StringBuffer and StringBuilder are mutable classes. StringBuffer operations are thread-safe and synchronized whereas StringBuilder operations are not thread-safe.StringBuffer is to be used when multiple threads are working on same String and StringBuilder in the single threaded environment.StringBuilder performance is faster when compared to StringBuffer because of no overhead of synchronized.
I hope you guys are clear with Java String, how they are created, their different methods and interfaces. I would recommend you to try all the Java String examples. Do read my next blog on Java Interview Questions which will help you set apart in the interview process.

Thanks for reading

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Further reading

Top 4 Spring Annotations for Java Developer in 2019

Java Tutorial for Absolute Beginners

100+ Java Interview Questions and Answers In 2019

Python vs Java: Understand Object Oriented Programming

Java Enum Tutorial - Enumeration in Java Explained

Java Enum Tutorial - Enumeration in Java Explained

This video on Java Enum Tutorial will provide you with detailed knowledge about Enumeration in Java along with real times examples for better understanding.

Java Enum Tutorial | Enumeration in Java Explained | Java Tutorial For Beginners

This informative video will include the following.

00:21 Agenda

00:55 What is Enum?

01:22 Why we need Enum?

06:45 Differences between Class and Enum

07:26 Syntax of Enum

07:43 Practical Examples of Enum

15:40 Advantages of using Enum

16:10 Enum Usecase: Rock Paper Scissor Game