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Java Mistakes (Neal) for Beginners

Conventions

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:

class
|
---- 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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