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Cheat Sheet

Author Me Date 2006/5/30

My notes on Java



  • class names begin with a capital letter
  • constants are all CAPS (final means no changes/compiler check)

Default values

  • numeric types = zero
  • char = '\u000'
  • class references or references to arrays = null

A class file contains object definitions and methods:

---- Variables
---- Methods
  • static variables are shared across the class
  • instance variables are for each instance of the object
  • public static void main() is the first executed object

modifiers = public, static, final, abstract, native, private, protected, synchronized

types are

value_type = void, integer, double, string, array, etc.

[Note: I'm not sure if it's KIOVI editor or this module that causes the extra spacing for this code to go away upon submission, but it's annoying.]

* This is a special doc comment.
* The javadoc program can yank these to create online
* documentation (notice the ** at the start)

* This is a standard set of comments

ClassName varname = new ClassName(); // how to define a new classed variable
modifier class ClassName {
static var = null;
vartype varname = null;

//method definition (return_type can be any - void returns nothing)
//static allows to get to the method even if the values are null
modifiers type methodName ( [type arg1], [type arg2], ..., [type argn]) {

//Executable code here
return return_value; //or return; for voids

class Sphere {
static final double PI = 3.141592638; // Class variable that has a fixed value
static int count = 0; // Class variable to count objects

// Instance variables
double radius; // Radius of a sphere
double xCenter; // 3D coordinates
double yCenter; // of the center
double zCenter; // of a sphere

// Static method to report the number of objects created
static int getCount() {
return count; // Return current object count

// Instance method to calculate volume
double volume() {
return 4.0/3.0*PI*radius*radius*radius;

// Instance method to change the radius
// Change the instance variable to the argument value void
changeRadius(double radius) {
this.radius = radius;

// Plus the rest of the class definition...

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(c) 2006-2007 - Mark Boyden
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