When we consider a Java program it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what do class, object, methods and instance variables mean.
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| First Java Program by Vandna Sharma: another name of JAVA |
- Object - Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.
- Class - A class can be defined as a template/ blue print that describes the behaviors/ states that object of its type support.
- Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
- Instance Variables - Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.
First Java Program:
Let us look at a simple code that would print the words Hello World public class MyFirstProgram {
/* This is my first java program.
* This will print 'Hello World' as the output
*/
public static void main(String []args) {
System.out.println("Hello World"); // prints Hello World
}
}
Let's look at how to save the file, compile and run the program. Please follow the steps given below:
- Open notepad and add the code as above.
- Save the file as: MyFirstProgram.java.
- Open a command prompt window and go o the directory where you saved the class. Assume it's C:\.
- Type ' javac MyFirstProgram.java ' and press enter to compile your code. If there are no errors in your code, the command prompt will take you to the next line (Assumption : The path variable is set).
- Now, type ' java MyFirstProgram ' to run your program.
- You will be able to see ' Hello World ' printed on the window.
C : > javac MyFirstJavaProgram.java
C : > java MyFirstJavaProgram
Hello World