Java Methods

1
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

2
Java Methods

• So when we say make a pizza we mean do all
  those instructions. Lucky for us we dont 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!
3
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.

4
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)
5
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
/
6
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)

7
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

8
Java Download Websites
No need to take notes here.
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 JCreator
http//www.cs.nyu.edu/courses/fall03/V22.0101-002/
instruc.html
9
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
Then to run your Applet you would type
appletviewer MyHtmlFile.html
Or you could simply open your HTML file with a
browser.