Java Methods

Methods contain a group of instructions that together perform a single task. For example if I want to perform the task of “making a pizza”, I would have to do the following:

1. Make the dough

2. Make the pizza sauce

3. Put sauce on the pizza

4. Put toppings on the pizza

5. Cook the pizza

Java Methods

So when we say “make a pizza” we mean do all those instructions. Lucky for us we don’t talk using such detail because conversations would take for ever!

If it takes one instruction to draw a single line how many instructions does it take to draw one of these polygons? Answer 6. How about 100 polygons? Answer 600. A Lot!

Java Methods

A Different approach to this polygon drawing problem is to create a method that draws an entire polygon. We can then use that method to draw as many polygons as we want. Methods cut down the number of instructions we have to write. They also make our programs a lot easier to read: if we place a set of instructions inside a method, the method name will indicate what all these instructions actually do. Being able to group instructions in this manner also makes our program easier to debug.

Java Methods // Comment: General structure of a Java method:

public void method_name (){ // instruction 1 // instruction 2 // instruction 3 // …}

// we can use our method inside the paint like thispublic void paint (Graphics screen){

}

Java Methods

Our method for drawing a polygon would look like this.

public void drawPolygon ()

{

/* instruction for drawing line 1 instruction for drawing line 2

instruction for drawing line 3

…

*/ }

Java Methods

Methods contain a group of related instructions for the computer. For the time being we will be using methods that already exist in Java. Later in the course we will be creating our own methods from scratch. Some example of already defined Java methods are:

• drawString(“Anything I want goes here”, x, y);• drawRect(width, height, x, y);• setColor(Color.blue);

The import Statement

Many useful Java Applet methods and variables are located in pre-made packages. If a programmer wants to use one of these methods or variables he or she must first import the package that it belongs to. Otherwise the compiler will not know where that special word came from. Import statements are used to import these useful packages. Examples of some Java special words we will be using are:

• Applet Java Applet Template (so we can create Applets)• Graphics Java Applet Variable (lets us draw to the screen)• paint Java Applet method• init Java Applet method• Color Variable

Java Download Websites

Java Developers Kit (Compiler)http://java.sun.com/j2se/1.4.2/download.html

JCreator: A Java Text Editor (For Windows)Be sure to select JCreator LE version http://www.jcreator.com/Download.htm

Instructions on installing JDK and JCreatorhttp://www.cs.nyu.edu/courses/fall03/V22.0101-002/instruc.html

No need to take notes here.

JDK Java Development Kit

The JDK is a free compiler for Java offered by Sun Microsystems. Project Builder is the visual interface for the compiler. In other words Project builder is a program that allows us to use the JDK in an easy (user-friendly) fashion. Project Builder provides us with, windows, buttons, command icons, text-editor etc. Otherwise we would have to use the command line to compile our Java source code. The command to compile Java source files using just the JDK (with no Project Builder) would be:

javac mySourceFile.java

appletviewer MyHtmlFile.html

Then to run your Applet you would type

Or you could simply open your HTML file with a browser.