What is a Java file?
A file containing Java source code and saved with .java file extension is known as Java file. The Java is one of the most widely used technology for the development of games, mobile, web and desktop applications. Since the Java is platform independent, it works flawlessly on Windows, Mac, Linux, Raspberry Pi, etc. The Java is very similar to C# and C++ so it is easier to switch between these languages.
Brief History
The Java project was initiated in June 1991 by James Gosling, Mike Sheridan, and Patrick Naughton. Java was initially named Oak. It was later renamed Green and finally to Java. James Gosling designed Java with a syntax similar to C/C++. The first public version of Java was released in 1996 by Sun Microsystems. It could run on all the popular systems which caused Java to become popular quickly. With the release of Java 2 in December 1998, multiple configurations for different types of platforms were built. The versions were as follows
- J2EE (Java EE): For enterprise solutions
- J2ME (Java ME): For mobile applications
- J2SE (Java SE): For desktop applications
On November 19, 2006, Java Virtual Machine (JVM) was released by Sun as free and open-source software. After Oracle Corporation acquired Sun Microsystems in 2009–2010, James Gosling resigned from Oracle on April 2, 2010.
How to run/execute Java code
To execute the Java code, it needs to be compiled first. For that, the Java SDK is required. The Java SDK compiles the Java code to a bytecode class file. There are IDE’s like Eclipse and IntelliJ Idea that makes it easier to work with Java files by providing code completion and easy to use interface to compile and execute the Java code.
Java File Format
The syntax of Java was highly influenced by C and C++ but unlike C++, Java was built almost exclusively as an object-oriented language. In Java, all the code is written inside classes and every data item is an object. In contrast to C++, Java does not support operator overloading or multiple inheritance.
Java sample code
The following is an example of Java syntax.
/*
The example code prints
Hello World from Java to the console.
*/
public class ExampleApp {
public static void main(String[] args) {
System.out.println("Hello World from Java"); // Prints the string to the console.
}
}
In the above code, the public keyword denotes the access modifier. It states that this class may be accessed by the classes outside the class hierarchy. The access modifier can also be protected (can be accessed in the same package) or private (the methods can only be accessed by the same class). The static in front of the method indicates that the method can be invoked without a specific instance of the class. The void indicates that the method would return nothing. To print the string to the console. System.out.println command is used. In this command, the System class has a static field out which is an instance of the PrintStream class containing the println method.
The file name of the Java files should be the same as the class name. So the Java file for the example code would be named ExampleApp.java.
