Your first Java program
In this chapter you will learn:
Create Java file
Let's start by compiling and running the following short sample program.
/* /*from j a v a 2s. c o m*/
This is a simple Java program. Call this file "Example.java".
*/
public class Example {
// Your program begins with a call to main().
public static void main(String args[]) {
System.out.println("Java.");
}
}
In Java, a source file is called a compilation unit. It is a text file that contains one or more class definitions. The Java compiler requires that a source file use the .java filename extension.
In Java, all code must reside inside a class. By convention, the name of the public class should match the its file name. And Java is case-sensitive.
Compiling the Program
To compile the program, execute the compiler, javac, specifying the name of
the source file on the command line:
C:\>javac Example.java
The javac compiler creates a file called Example.class.
Example.class contains the byte code version of the program.
To run the program, use the Java interpreter, called java.
Pass the class name Example as a command-line argument, as shown here:
C:\>java Example
When the program is run, the following output is displayed:
When Java source code is compiled, each individual class is put into its own file named classname.class.
A Closer Look at the Example.java
The first part is a comment.
/*
This is a simple Java program. Call this file "Example.java".
*/
Comment is a remark for a program. The contents of a comment are ignored by the compiler. The next line of code in the program is shown here:
public class Example {
The keyword class declares that a new class is being defined.
Example is the name of the class.
The entire class definition is between the opening curly brace ({) and the closing curly brace (}).
The next line in the program is the single-line comment, shown here:
// Your program begins with a call to main().
A single-line comment begins with a // and ends at the end of the line.
The next line of code is shown here:
public static void main(String args[]) {
Java applications begin execution by calling main(String args[]).
Java is case-sensitive. Thus, Main is different from main.
Next chapter...
What you will learn in the next chapter:
- How to define variables and store value into them
- How to define more variables and separate them with comma
- How to code block