Difference between a java program and a java class

Question

Hi there,
What is the difference between a java program and a java class?

Answer 1

HI,
A java class is an object - described in a .class file - which has been given properties and behaviours and which can be instantiated in a program.
A java program( application ) consists of at least one class (one of which must be declared public) and which executes its main() method ( of the public class ) when it is started.
Every program is a class but not every class is a program.
Examples:
A java program
// this simple program will print out the first command line argument you put
// in after calling : java ScreenWriter "arguments"
class ScreenWriter
public static void main( String [] args )
if( args.length > 0 )
System.out.println( args[0] );
A java class
//the Math class is already defined in the java.lang package
//and contains a constant for PI
//So I can include the Math class with the PI constant in my simple program
//and now I have a program that involves my ScreenWriter class and the Math class too.
class ScreenWriter
public static void main( String [] args )
if( args.length > 0 )
System.out.println( args[0] );
System.out.println( "The value of Pi is: " + Math.PI );
When you see package and import declarations at the start of a program they are there to ensure the compiler knows which classes are used in the program.
Hope that helps,
Terry