Java Hello World 

Java Hello World 


Click on RUN button to see the output

Java online compiler

Write, Run & Share Java code online using OneCompiler's Java online compiler for free. It's one of the robust, feature-rich online compilers for Java language, running the latest Java LTS version which is Java 11. Getting started with the OneCompiler's Java editor is easy and fast. The editor shows sample boilerplate code when you choose language as Java and you can also choose hundreds of reference programs to get started. For example, if you want to write a program on Java collections choose the collections tag from reference and see hundreds of pre-written programs on collections. You can pick one of them to start your coding.

Taking inputs (stdin)

OneCompiler's Java online editor supports stdin and users can give inputs to the programs using the STDIN textbox under the I/O tab. Using Scanner class in Java program we can read the inputs. Following is a sample program that shows reading STDIN ( A string in this case ).

import java.util.Scanner;
class Input {
    public static void main(String[] args) {
    	Scanner input = new Scanner(;
    	System.out.println("Enter your name: ");
    	String inp =;
    	System.out.println("Hello, " + inp);

Adding dependencies

OneCompiler supports Gradle for dependency management. Users can add dependencies in the build.gradle file and use them in their programs. When you add the dependencies for the first time, the first run might be a little slow as we download the dependencies but the subsequent runs will be faster. Following sample Gradle configuration shows how to add dependencies

apply plugin:'application'
mainClassName = 'HelloWorld'

run { standardInput = }
sourceSets { main { java { srcDir './' } } }

repositories {

dependencies {
    // add dependencies here like following
    compile group: 'org.apache.commons', name: 'commons-lang3', version: '3.9'

About Java

Java is a very popular general-purpose programming language, it is class-based and object-oriented. Java was developed by James Gosling at Sun Microsystems ( later acquired by Oracle) the initial release of Java was in 1995. Java 11 is the latest long-term supported version (LTS). As of today, Java is the world's number one server programming language with a 12 million developer community, 5 million students studying worldwide and it's #1 choice for the cloud development.

Syntax help


1. If Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
  // code
} else {
  // code

2. Switch:

Switch is an alternative to If-Else-If ladder and to select one among many blocks of code.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
 //code to be executed when all the above cases are not matched;    

3. For:

For loop is used to iterate a set of statements based on a condition. Usually for loop is preferred when number of ierations is known in advance.

for(Initialization; Condition; Increment/decrement){  

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of ierations is not known in advance.

 // code 

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition); 

Classes and Objects

Class is the blueprint of an object, which is also referred as user-defined data type with variables and functions. Object is a basic unit in OOP, and is an instance of the class.

How to create a Class:

class keyword is required to create a class.


class Mobile {
    public:    // access specifier which specifies that accessibility of class members 
    string name; // string variable (attribute)
    int price; // int variable (attribute)

How to create a Object:

Mobile m1;

How to define methods in a class:

public class Greeting {
    static void hello() {
        System.out.println("Hello.. Happy learning!!");

    public static void main(String[] args) {


Collection is a group of objects which can be represented as a single unit. Collections are introduced to bring a unified common interface to all the objects.

Collection Framework was introduced since JDK 1.2 which is used to represent and manage Collections and it contains:

  1. Interfaces
  2. Classes
  3. Algorithms

This framework also defines map interfaces and several classes in addition to Collections.


  • High performance
  • Reduces developer's effort
  • Unified architecture which has common methods for all objects.
SetSet is a collection of elements which can not contain duplicate values. Set is implemented in HashSets, LinkedHashSets, TreeSet etc
ListList is a ordered collection of elements which can have duplicates. Lists are classified into ArrayList, LinkedList, Vectors
QueueFIFO approach, while instantiating Queue interface you can either choose LinkedList or PriorityQueue.
DequeDeque(Double Ended Queue) is used to add or remove elements from both the ends of the Queue(both head and tail)
MapMap contains key-values pairs which don't have any duplicates. Map is implemented in HashMap, TreeMap etc.