more java @ mlab, 10-17 Jan 2000, juhuu@katastro.fi



 Objects (Classes)


	Objects in java are called classes. Classes
	can contain data and methods. These are referred
	to as class members


	Example of defining a class:

	// import all the classes you need to use. all the 
	// classes in the same directory are imported automatically.
	// importing doesn't affect the size of the class, it merely
	// tells that the names of the classes to be used.
	//
	// in this example, we need java.awt.Image. the easy way to import
	// it is to use * (java.awt.*), it imports all the classes found in
	// awt package.

	import	java.awt.*;

	//  the name of the class is Human (the names usually start with capital letter)
	public class Human
	{
		// this class has 3 data members
		int	nWeight;
		String	sName;
		Image	imgPhoto;

		// the class constructor
		//
		// this method creates an instance of the class Human
		public Human (int weight, String s, Image img)
		{
			nWeight 	= weight;
			sName 		= s;
			imgPhoto 	= img;
		}

		// a method (function). this methods prints
		// the weight of the Human to java console
		// 
		// void means that this method doesn't return a value.
		public void print_weight()
		{
			System.out.println("I weight: " + nWeight);
		}
	}
	// end of class Human

	
	// example of using class Human from another class
	public class OtherClass
	{
		// we have one Human variable called 'friend'
		Human	friend;

		public init ()
		{

			// put a new Human instance to friend
			friend = new Human(72, "Petteri", image_of_petteri);

			// call the print_weight function of the friend (Petteri)
			friend.print_weight();

			// we can change the friend ; after this, the reference to Petteri is lost
			friend = new Human(80, "Jukka", image_of_jukka);

			// now we print the weight of Jukka
			friend.print_weight();
		}
	}