An online compiler is a tool which allows us to compile the source code and execute it online. This is a great option, especially for new Java students, tutors, or interviewers. This is a great option, especially for new Java students, tutors, or interviewers.
A Java compiler is a compiler for the programming language Java. The most common form of output from a Java compiler is Java class files containing platform-neutral Java bytecode, but there are also compilers that output optimized native machine code for a particular hardware/operating system combination.
Most Java-to-bytecode compilers, Jikes being a well known exception, do virtually no optimization, leaving this until run time to be done by the JRE.[citation needed]
The Java virtual machine (JVM) loads the class files and either interprets the bytecode or just-in-time compiles it to machine code and then possibly optimizes it using dynamic compilation.
A standard on how to interact with Java compilers programmatically was specified in JSR 199.
Major Java compilers[edit]
As of 2019, the following are major Java compilers:[citation needed]
- The Java Programming Language Compiler (javac), included in the Java Development Kit from Oracle Corporation, open-sourced since 13 November 2006.
- Eclipse Compiler for Java (ECJ), an open source incremental compiler used by the Eclipse project.
References[edit]
External links[edit]
- JSR 199 Java Compiler API Java Specification Request for invoking the Java compiler from a Java program
- Stephan Diehl, 'A Formal Introduction to the Compilation of Java', Software - Practice and Experience, Vol. 28(3), pages 297-327, March 1998.
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It's time to write your first application! The following instructions are for users of Windows Vista, Windows 7, and Windows 8. Instructions for other platforms are in 'Hello World!' for Solaris OS and Linux and 'Hello World!' for the NetBeans IDE.
If you encounter problems with the instructions on this page, consult the Common Problems (and Their Solutions).
- Creating Your First Application
A Checklist
To write your first program, you'll need:
- The Java SE Development Kit 8 (JDK 8)You can download the Windows version now. (Make sure you download the JDK, not the JRE.) Consult the installation instructions.
- A text editorIn this example, we'll use Notepad, a simple editor included with the Windows platforms. You can easily adapt these instructions if you use a different text editor.
These two items are all you'll need to write your first application.
Creating Your First Application
Your first application,
HelloWorldApp
, will simply display the greeting 'Hello world!'. To create this program, you will: - Create a source fileA source file contains code, written in the Java programming language, that you and other programmers can understand. You can use any text editor to create and edit source files.
- Compile the source file into a .class fileThe Java programming language compiler (
javac
) takes your source file and translates its text into instructions that the Java virtual machine can understand. The instructions contained within this file are known as bytecodes. - Run the programThe Java application launcher tool (
java
) uses the Java virtual machine to run your application.
Create a Source File
To create a source file, you have two options:
- You can save the file
HelloWorldApp.java
on your computer and avoid a lot of typing. Then, you can go straight to Compile the Source File into a.class
File. - Or, you can use the following (longer) instructions.
First, start your editor. You can launch the Notepad editor from the Start menu by selecting Programs > Accessories > Notepad. In a new document, type in the following code:
Be Careful When You Type
Note: Type all code, commands, and file names exactly as shown. Both the compiler (
javac
) and launcher (java
) are case-sensitive, so you must capitalize consistently.HelloWorldApp
is not the same as helloworldapp
.Save the code in a file with the name
HelloWorldApp.java
. To do this in Notepad, first choose the File > Save As menu item. Then, in the Save As dialog box:- Using the Save in combo box, specify the folder (directory) where you'll save your file. In this example, the directory is
myapplication
on theC
drive. - In the File name text field, type
'HelloWorldApp.java'
, including the quotation marks. - From the Save as type combo box, choose Text Documents (*.txt).
- In the Encoding combo box, leave the encoding as ANSI.
When you're finished, the dialog box should look like this.
The Save As dialog just before you click Save.
Now click Save, and exit Notepad.
Compile the Source File into a .class File
Bring up a shell, or 'command,' window. You can do this from the Start menu by choosing Run... and then entering
cmd
. The shell window should look similar to the following figure.A shell window.
The prompt shows your current directory. When you bring up the prompt, your current directory is usually your home directory for Windows XP (as shown in the preceding figure.
To compile your source file, change your current directory to the directory where your file is located. For example, if your source directory is
myapplication
on the C
drive, type the following command at the prompt and press Enter:Now the prompt should change to
Note:C:myapplication>
.To change to a directory on a different drive, you must type an extra command: the name of the drive. For example, to change to the
myapplication
directory on the D
drive, you must enter D:
, as follows:If you enter
dir
at the prompt, you should see your source file, as follows:Now you are ready to compile. At the prompt, type the following command and press Enter.
The compiler has generated a bytecode file,
HelloWorldApp.class
. At the prompt, type dir
to see the new file that was generated as follows:Now that you have a
.class
file, you can run your program.If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).
Run the Program
In the same directory, enter the following command at the prompt:
You should see the following on your screen:
Congratulations! Your program works!
If you encounter problems with the instructions in this step, consult the Common Problems (and Their Solutions).