Online Java Compiler

To start your programming journey you first need to understand what compilers are. Compilers are the computer software that converts your high-level source code to executable machine-level instructions made up of 0s and 1s, that can be understood by the computer.

Compilers scan the high-level code line by line and show different kinds of errors present in the code in the command line.

A Java compiler is software that can take a source code of Java written by a developer and then translate it into a platform-independent Java file. Java compilers include the Java Programming Language Compiler (javac), the GNU Compiler for Java (GCJ), the Eclipse Compiler for Java (ECJ), and Jikes.

Scaler Topics online compiler supports the latest versions of Java and, programmers can write, run, debug and share code snippets seamlessly.

It is one of the most robust & easy-to-use Java online Compilers. Owing to the fact that it has a plethora of features to offer to the budding Java programmers of today & extremely easy to get going, we have strived to create the best online Java compiler.

Working of the Java Compiler (IDE)

Given below are some of the steps of our Compiler that users might find helpful:

The first step is your need to sign in to use this compiler's features. It is possible to run your code without signing in but you will not have a track to your previous codes here, so it's advisable to sign in to enjoy its cool features. Click on the button present at the top right corner and a window will appear.

  • Code Editor: Write code in the code editor (which has syntax highlighting for more code readability). For users who are logged into the Scaler Topics Platform, the total number of characters in their code can go up to five thousand characters. For non Scaler Topics Users, their Java code can have up to five hundred characters.
  • RUN: In order to run a Java program, a user can write Java code in the editor and then click on the ‘RUN’ button after selecting the appropriate compiler version.
  • SAVE: The Java code written in the editor can be saved by clicking on the ‘SAVE’ button on the top right corner of the webpage. The saved codes can be accessed using the ‘MY SNIPPETS ’ button of the webpage. -** STDIN & STDOUT**: In order to feed input to the Java Code, users can use the Standard Input (stdin) console of our compiler and the output of the code appears on the Standard Output (stdout) of the compiler.
  • SAVE: The programs saved can be made public - available for all - or private - accessible to only the code owner.
  • FORK: Public code snippets can also be forked or downloaded in the ‘NEW’ section using the ‘FORK’ button. After forking a code, one can reuse it as per requirement.
  • SHARE: Now that you have your code ready, you might need to share it with people. Our compiler also supports sharing of code in Read-Only Format. This can be done using the ‘SHARE’ button on the top right corner of the webpage.


What is Java and Why Learn?

With an initial release in the year of 1995, the Java programming language is one of the oldest high-level, object-oriented programming languages of today. It was developed by James Gosling at Sun Microsystems, which has now been acquired by Oracle.

It is an object-oriented computer programming language that supports a plethora of features like structured programming, lexical variable scope, and recursion, with a static type system.

Java is one of the most popular languages of today and a lot of Multinational Companies have their legacy code bases written in Java. Java is extremely easy to work with and has support for a lot of things, be it working with operating systems or file storage, databases, or distributed systems.

Java Syntax

Please find below a list of basic syntaxes which can be used to write a Java program and can be run using a JDK Java compiler:

Syntax of Branching or Control Flow Statements:


In order to do branching of your program on the basis of one or more conditions, the if-else statements can be used. The syntax of the if-else statement is given below.


At times there might be multiple conditions that need to be checked if one condition fails. For this, we can also use the if else-if else statements. The syntax for the same is given below:

Switch Case

If a lot of branching is required for your Java program, then the if-else statements can make the code look ugly and less readable. To avoid this, we can use the switch statement. Given below is the syntax for the switch statement.


Syntax of Loops in Java

In order to execute a set of Java statements repeatedly, a loop can be used. Given below are the syntaxes of different types of loops in Java:

for loop


while loop


do-while loop


Syntax of Arrays in Java

If we need to store multiple elements of the same data type together, we can use the Array data structure of the Java programming language. Arrays are stored in contiguous memory addresses and array values can be fetched using indices. The indexing in arrays ranges from 0 to size-1.

Arrays can be of any dimension in general. But the most popularly used arrays are one-dimensional and two-dimensional arrays. Given below is the syntax to declare an array.

Syntax to declare a One Dimensional Array:

Syntax to declare a Two Dimensional Array:

Syntax of Functions in Java

If a piece of code needs to be reused again and again in different parts of our Java program, the features of Functions in Java can be used. A set of statements are written in functions, which can be called from various parts of the program. This increases the modularity of the code written and also supports code reusability.

Functions are of two types:

  • Library Functions: Library functions are those functions that are built-in in the Java programming language. These functions are present in various packages and can be imported into our Java code using the import keyword. For example, the standard input and output files containing the functions for standard input and output can be included in our Java code as follows:
  • User-Defined Functions: User-defined functions are those functions that are written by Java programmers based on the requirement of their logic.

Functions in Java programs can be declared as follows:

Functions in Java programs can be defined as follows:

Functions in Java programs can be called from any part of the Java code as follows:

Syntax of Creation of Classes and Objects in Java

As mentioned previously, Java is an object-oriented programming language and every piece of code needs to be written in classes, also known as ‘Object Factories’. Classes are blueprints of objects and can be declared using the ‘class’ keyword. An example of creating a class in Java is given below:

In order to create objects of the above-mentioned Class, the following statement can be used:

Collections in Java

In order to bring a unified common interface to all the objects, Java Collections can be used. Collections are objects of similar types which can be represented as a single unit. The Collection Framework of Java was introduced in JDK 1.2 which was used to represent and manage Collections. It consists of the following:

  • Classes
  • Interfaces
  • Algorithms

Some of the most commonly used collections of Java are as follows:

  • List: List is an ordered collection of elements that may or may not have duplicates. Lists are classified into ArrayList, LinkedList, Vectors.
  • Set: Sets are a collection of elements that do not contain duplicate values. They can be implemented using HashSets (unordered), LinkedHashSets, TreeSets(ordered), etc.
  • Map: Maps are a collection of elements containing key-value pairs which do not contain duplicate values. They can be implemented using HashMaps (unordered), LinkedHashMaps, TreeMaps(ordered), etc.
  • Queue: Queue is a data structure that follows the First In First Out principle (FIFO). They can be implemented using a LinkedList or a PriorityQueue.
  • Dequeue: Deque(Double Ended queue) is used to add or remove elements from both the ends of the Queue(both head and tail)

How to Write a Program in Java?

In order to write a program in Java, one can use any of the above features provided by the Java programming language mentioned above. The entry point of a Java program is always the main() function. In order to import the standard input and output library functions, one can include the “” package. The main() function usually has a return type as void. Given below is a sample Java code to get you started with Java programming:

How to Compile and Run the Java Programs Online?

For the Scaler Topics online compiler, it is very easy to compile and run the Java program. One can just write the code in the editor and then click on the ‘RUN’ button in order to run and compile it. The standard output console shows the output of the Java program.

Additional Resources


  • Online IDE: IDE is an acronym for Integrated Development Environment. Online Integrated Development Environments help programmers code in various languages and run, compile and debug their codes online without having the need to download the respective programming compilers.
  • Compiler: In computing, a compiler is a computer program that is used to translate computer codes written in one programming language into another language.
  • Interpreter: Like Compilers, interpreters are also used to translate computer codes written in one programming language into another language. However, the difference between the two is that compilers compile the entire source code into machine code at once while interpreters convert the source code into machine code line by line.
  • Code Editor: A code editor is software used by programmers to code. Most code editors provide various features like syntax highlighting to make the code written on them more readable.
  • Coding Ground: Coding grounds are platforms that can be used to write and run codes written in various languages.