CSC/ECE 517 Fall 2011/ch3 3h ss

Introduction

In any programming language, the data type refers to the class of data which contains specific type or range of values. Data types are used along with variables used in the program. The data type tells us what kind of values the variable can store, what is the range of the values and how much space the values take in memory etc.

The primitive data types refer to the built-in data types which are supported by the programming language. Often 'data types' and 'primitive data types' are used interchangeably. But not all data types are primitive. Programming languages have some non-primitive data types or derived data types which are provided by the language by making use of its primitive data types.

Many object-oriented programming languages provide support for primitive data types while some object-oriented programming languages provide support for primitive objects along with primitive types.

Definition

Primitive objects refer to the objects of built-in classes which provide the same functionality or rather more functionality than the primitive types. Some object-oriented programming languages provide support for only primitive objects (i.e., all primitive types are objects).

The common built-in data types are integers, floating point numbers, characters, strings and boolean.

Different object-oriented programming languages implement these primitive data types and primitive objects in a different manner.

Primitive objects in different OO languages

Java

In Java, there are 8 primitive types: boolean, char, byte, short, int, long, float, and double

For each of these primitive types, Java provides wrapper classes to create primitive objects which wrap the primitive data values. A wrapper not only contains the primitive data value, but it also defines properties and methods that can be used to manipulate that data. In Java, the primitive values are not implicitly converted to primitive objects. Instead, methods are provided for doing explicit conversion. The primitive objects are stored on heap in memory while the variables containing primitive values are stored on heap.

Primitive Type	Wrapper Class	Size
boolean	Boolean	1-bit
char	Character	16-bit
byte	Byte	8-bit
short	Short	16-bit
int	Integer	32-bit
long	Long	64-bit
float	Float	32-bit
double	Double	64-bit

Example:

   int i = 10;
   int ii = 20;
   Integer I = new Integer(i);
   Integer II = new Integer(ii);
   System.out.println(I+II);            
   System.out.println(I.equals(II));    

Output:

   30
   false

C#

C# is a strongly typed language, where it is necessary to declare the data type of a variable and also be aware of the data type conversion. C# provides a significant number of primitive data types. See [1]

Because C# represents all primitive data types as objects, it is possible to call an object method on a primitive data type. For example:

   static void Main()
   {
       int x = 7;
       object o = x;
       System.Console.WriteLine(o.ToString());
   }

Some data types (e.g. Decimal and String) can appear like primitives at first sight, but are actually not. So it is important to exercise caution before making such assumptions. To test whether a particular type is a primitive or not you can use the property Type.IsPrimitive.

Consider the following example:

   if (t.IsPrimitive)    // where t is the type
   {
       // Is Primitive
   } else if (t == typeof(Decimal))
   {
       // Is Decimal
   } else if (t == typeof(String))
   {
       // Is String
   } else
   {
       // Other type
   }

JavaScript

There are 5 primitive data types in JavaScript: string, number, boolean, null and undefined.

For string, number and boolean values, there are corresponding classes just like in Java to create primitive objects which wrap the primitive values.

Primitive Type	Wrapper Class	Range
string	String
number	Number
boolean	Boolean

In JavaScript, the primitive value is implicitly converted to a primitive object whenever some tries to acccess a property or invoke a method on the primitive value and the primitive object is used in place of the primitive value. Since the object contains properties and methods, the use of primitive value as an object succeeds. After the property is accessed or the method is processed, the primitive object is no longer needed and hence discarded. The same is true for the other primitive types and their corresponding primitive objects.

Example:

   var upperCaseString = "APPLE";
   var lowerCaseString = upperCaseString.toLowerCase();  // assigns string "apple" to lowerCaseString 
   var s = "Hello"
   var len = s.length;                                   // assigns value 5 to len

Ruby

Since Ruby is a pure object oriented language, everything in Ruby is an object. Hence, all primitive types such as integers, floating point numbers, strings, are objects of a built-in class. All integers are primitive objects of either class Fixnum or Bignum. A numeric literal with a decimal point and/or an exponent is a primitive object of Float. Single quoted literals and double quoted literals are primitive objects of String.

Example:

   puts 10.class
   puts 7.45.class
   puts 'hi'.class
   puts "hello".class

Output:

   Fixnum
   Float
   String
   String

This indicates that 10 is converted into an object of type Fixnum, 7.45 is converted into an object of type Float, 'hi' and "hello" are both converted into an object of type String.

Since all primitive types in Ruby are objects, we should be able to call methods of the Object class on them. Let us demonstrate the same for integer and float using the following example:

   a=10
   puts a.to_f  
   b=20.5
   puts b.to_i

Output:

   10.0
   20