Home : Course Map : Chapter 3 : Java :
Class Data Fields
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Chapter 3

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Class Definition
Data Fields
Methods
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Instantiation
  Demo 1
  Demo 2
Static Members
  Demo 3
Value&Reference
  Demo 4
Overloading
   Demo 5
Wrappers 
  Demo 6
Autobox/Unbox
   Demo 7
Arrays
  Demo 8
Exceptions
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A class definition typically includes one or more fields that declare data of various types. For example, this code shows a class with a single int datum:

public class GenericClass
{
  int x = 0;





  public int getX ()
  {
    return x;
  }

  public void setX (int i)
  {
    x = i;
  }


}



Field with a declaration of an integer data variable. This instance variable is accessible to all methods in the class.

A method to obtain the value of the x variable.
 
 
 
A method to set the value of the x variable.


This data is accessible to all the methods in the class. Here, for example, the getX() method returns the value in the x variable and the setX(int i) method sets x to the value passed in the method argument.

When the data field declaration does not assign an explicit value to the data, default values will be used:

  • int, byte, short, char - default value 0
  • float, double - default value 0.0
  • boolean - default value false

public class GenericClass
{
  int i;
  double d = 1.3;
  boolean b = true;
 ...

}



Fields can use either the default values or explicit initialization

 

We mentioned in Chapter 2 identifer rules for naming field data: identifiers cannot begin with a number and cannot contain a punctuation character or any character listed in the Reserved Symbols Table. Underscore _ and the dollar sign $ are allowed.

Latest update: Oct. 17, 2004

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