Java: Print String

Here's our first program, printing a string.

/*
  this is comment.
*/

// also comment

public class PrintMe {
    public static void main(String[] args) {
        System.out.println("yes");
    }
}

1. Save it to a file and name it PrintMe.java.
2. Then compile it by running javac PrintMe.java. This will create a file named PrintMe.class. It is the compiled code.
3. To run the program, type java PrintMe in the terminal. Then it should print the string.

Some Syntax Details

Note the keyword class in the code. A Class is like a boxed set of functions and data.

The “PrintMe” is the class's name. The public specifies that the class can be called by other classes/functions.

The static means that this class can be called without having to create an instance of it first.

The main is a function of this class. Functions defined inside a class is called the class's “method”. “main” is the primary method of any program. That is, there is one “main” method in any Java program.

The main(String[] args) declares that the “main” method takes a argument of string type.

Do not worry about these details. We'll cover them each later. If you are not clear about the general concepts of Object Oriented Programing, you should now read: Object Oriented Programing (OOP) Jargons and Complexities .

General Structure of Java Code

In general, ALL Java source code have the following structure:

/*
  comment
*/

// Declaring this file to be a package.
// All Java source code belongs to some package.
// Only trivial, testing code does not declare a package.
// When a source file does not declare a package, it is said be a “unnamed” package
package abc.def.sounds;

// load packages you need
import java.awt.Cursor;

// a bunch of class definitions
class MyClass1 {
    // code
}

class MyClass2 {
    // code
}

// more classes

// The main class.
// The file name must be the same as this class name
public class MyMainClass {
    public static void main(String[] args) {
        //body
    }
}

Class Name synced to File Name

For now, remember the following:

There must be one public class definition in the file that has the same name as the file name. For example, if your file name is XYZ.java, then one of your class must be named “XYZ”.