CSC/ECE 517 Fall 2012/ch1 1w21 aa

Primitive objects in object-oriented languages - based on the wiki page from previous year

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.

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

• Integers - Integers represent the whole numbers which can be positive or negative or zero, e.g. 9999, 0, -25, etc.
• Floating point numbers - Floating point numbers represent the numbers which are fractions or contain floating-decimal points, e.g. -3.002, 2.5, 22.0, etc.
• Characters - Characters represent any single letter, number, space, punctuation mark, or symbol that can be typed on a computer, e.g. 'a', '9', ' ', '!' , '\n', etc.
• Strings - Strings represent the sequences of characters or simply any text, e.g. "Hello!", "9 am to 6 pm", etc.
• Booleans - Booleans represent the true or false values. Sometimes, instead of true and false, 1 and 0 are used to represent the boolean values.

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 more functionality than the primitive types. Some object-oriented programming languages provide support for only primitive objects (i.e., in such languages all primitive types are objects).

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

Primitive objects in different OO languages

C++

C++ is a statically typed, objected oriented programming language. It is widely used on a lot of hardware and software platforms. As C++ just adds object oriented features and a few other enhancements to C, the primitive data types that it provides are same as those provided by C<ref>http://en.wikipedia.org/wiki/C%2B%2B C++ an extension of C</ref>. They are described below <ref>http://en.cppreference.com/w/cpp/language/types List of C++ data types</ref>.

Name	Description	Size	Range
int	Basic numerical data. Can have modifiers that vary size and range.	4 bytes	-2,147,483,648 to 2,147,483,647
char	Can hold one character of data like an alphabet, number, or symbol represented in ASCII	1 byte	-128 to 127
wchar_t	used for storing compiler-defined wide characters and unicode characters <ref>http://en.wikipedia.org/wiki/Wide_character Wide Character in C++ </ref>	compiler defined	compiler defined
float	single precision floating-point	4 bytes	± 3.402,823,4 * 10^38
double	double precision floating-point	8 bytes	+/–1.7 * 10^308
bool	represents logical values	1 byte	true/false
void	generic identifier that does not identify type	Does not exist	Does not exist

C++ allows variables of any of these data types to be created and also supports using these data types to construct complex data types like structures and classes. C++ also allows pointers that can be used to store the address of a variable of any simple or complex data type.

Java

There are 8 primitive data types defined in java which are as follows<ref>http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html Java data types</ref>:

Name	Description	Size(in bits)	Range	Usage	Default Value
byte	Signed two's complement integer	8 bits	-128 to 127	This datatype can be used in arrays where there is a space constraint to save memory.	0
short	Signed two's complement integer	16 bits	-32,768 to 32,767	This datatype can also be used to save memory in large arrrays.	0
int	signed two's complement integer	32 bits	-2,147,483,648 to 2,147,483,647	This datatype is generally the default datatype for all the numbers we use in our program.	0
long	signed two's complement integer	64 bits	-9,223,372,036,854,775,808 to 9,223,373,036,854,775,807	This type is used when we require a value that is outside the range of values provided by int.	0L
float	Single-precision IEEE 754 floating point	32 bits	32-bit IEEE 754 floating-point numbers.	Use this datatype to save memory in large arrays.	0.0f
double	Double-precision 64-bit IEEE 754 floating point	64 bits	64-bit IEEE 754 floating-point numbers.	This data type is generally the default for decimal values.	0.0d
boolean	Boolean	1- bit	false, true	Use this data type for flags that track a true or false condition.	false
char	a char is a single 16-bit character encoded using Unicode	16 bit	Unicode character \u0000(0) through unicode character \uffff(65,535)	This type is used to define single characters.	'\u0000'

Besides these 8 primitive data types java provides support to character strings through Java.lang.String class. String is not a primitive datatype but its usage and functionality makes us think of it being so. One of the major differences in Java from the other languages is that,the size of variables of these primitive types do not vary from one system to another, ie, it is not machine/architecture dependent. Also, Java does not allow numeric values to be stored unsigned<ref>http://www.idevelopment.info/data/Programming/java/miscellaneous_java/Java_Primitive_Types.html Java Primitive datatypes </ref>.

Also, 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 stack.<ref>http://www.informit.com/articles/article.aspx?p=31755&seqNum=8 Stack and Heap memory</ref>

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

To find out if these wrapper classes are primitive or not, we can use the isPrimitive() method.

   System.out.println(INTEGER.TYPE.isPrimitive());
   System.out.println(BOOLEAN.TYPE.isPrimitive());

Output:

   true
   true

In Java, the comparison operations work in the same way on the primitive objects as well as any other class objects but different on the primitive types. The == operator when used on objects checks whether they refer to the same object but when used on variables of primitive types checks whether they contain the same value.<ref>http://leepoint.net/notes-java/data/expressions/22compareobjects.html Comparisons in Java</ref>

Example:

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

Output:

   false
   true

C#

C# is a statically-typed object oriented programming language. C# provides all the data types that are available in Java, and adds support for unsigned numerals and a new 128-bit high-precision floating-point type. All primitive data types in C# are objects in the System namespace. The various primitive data types in C# are defined below<ref>http://msdn.microsoft.com/en-us/library/ms228360(v=vs.80).aspx C# data types </ref>:

Name	.NET Class	Size	Description	Range
byte	System.Byte	8 bits	8-bit unsigned integral type.	0 to 255
sbyte	System.SByte	8 bits	signed two's complement integer	-128 to 127
short	System.Int16	16 bits	16-bit signed integral type.	-32,768 to 32,767
ushort	System.UInt16	16 bits	16-bit unsigned integral type.	0 to 65,535
int	Int32	32 bits	signed two's complement integer	-2,147,483,648 to 2,147,483,647
uint	System.Int32	32 bits	32-bit signed integral type.	0 to 4,294,967,295
long	System.Int64	64 bits	64-bit signed integral type.	-9,223,372,036,854,775,808 to 9,223,373,036,854,775,807
ulong	System.UIint64	64 bits	64-bit unsigned integral type.	0 to 18,446,744,073,709,551,615
float	System.Single	32 bits	Single-precision floating-point type.	-3.402823e38 to 3.02823e38
double	System.Double	64 bits	Double-precision floating-point type.	-1.79769313486232e308 to 1.79769313486232e308
bool	System.Boolean	1 bit	Logical Boolean type	false, true
char	System.Char	16 bits	A 16-bit Unicode character.	Unicode character \u0000 through unicode character \uffff
object	System.Object	N/A	Ultimate base type of all other types.	N/A
string	System.String	N/A	A sequence of Unicode characters.	N/A
decimal	System.Decimal	128	Precise decimal with 28 significant digits.	±1.0 × 10e−28 to ±7.9 × 10e28

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.<ref>http://condor.depaul.edu/sjost/ndp/notes/cs1/CSDatatypes.htm C# Primitive Datatypes</ref><ref>http://www.java2s.com/Tutorial/CSharp/0040__Data-Type/PrimitivesinC.htm Primitives in C#</ref>

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. <ref>http://oreilly.com/javascript/excerpts/learning-javascript/javascript-datatypes-variables.html JavaScript Data Types and Variables</ref>

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
string	String
number	Number
boolean	Boolean

In JavaScript, the primitive value is implicitly converted to a primitive object whenever someone tries to access 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.<ref>http://ruby-doc.org/docs/ProgrammingRuby/html/builtins.html Classes in Ruby</ref> Some of the basic classes are:

Name	Description	Range
Integer	base class for FixNum and BigNum <ref>http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_integer.html Integer in Ruby </ref>	depends on FixNum and BigNum
FixNum	store integer values that fit in a native machine word<ref> http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_fixnum.html Fixnum</ref>	± 2^30 (for 32-bit systems)
BigNum	store Integer values larger than FixNum<ref>http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_bignum.html Bignum</ref>	values > 2^30 (for 32-bit systems)
String	sequence of characters/bytes<ref>http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_string.html String </ref>	Does not exist.
Float	real numbers with double precision floating point precision<ref>http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_float.html Float </ref>	± 1.7976 * 10^308 (for 32-bit systems)
TrueClass	represents logical true value<ref>http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_trueclass.html TrueClass </ref>	true
FalseClass	represents logical false value<ref>http://ruby-doc.org/docs/ProgrammingRuby/html/ref_c_falseclass.html FalseClass</ref>	false

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

Advantages of using primitive data types

The various advantages of using primitive data types are as follows:

Efficiency

Use of primitive data types takes less time to execute than a similar program that executes using object types. This is mainly because, when using object types, a lot of function calls are done implicitly to get the variables necessary for the operation. Consider the following example,

Integer a = new Integer(20);
Integer b = new Integer(30);
Integer c = a + b;

When a+b is executed, the line implicitly changes to c.valueOf(a.intValue() + b.intValue()) on the right hand side<ref>http://chaoticjava.com/posts/autoboxing-tips/ Autoboxing in Java</ref>. This increases the number of function calls and so takes up more time to execute. This is the case for all objects. This delay is not present when primitive data types are used as the actual data is fetched from memory instead of calling another function to retrieve it.

Using primitive data types is much more efficient way of programming than programming using objects<ref>http://today.java.net/pub/a/today/2005/03/24/autoboxing.html#performance%5Fissue autoboxing performance issues</ref>. For example, in Java when we use boxing in a loop it causes certain performance issues and is inefficient compared to using the primitive types directly. For more details and a sample program see this. Also, the discussion in this page describes just how the use of wrapper classes in Java takes up more memory during run time than when using primitive objects. It also provides sample programs to see this difference in our systems.

Simplicity

Working with primitive data types is more intuitive.

Example: 1. As a counter in a loop. Using objects in this place would make the program difficult to understand and tedious for the programmer.

(int i=0;i<10;i++)

2. In conditional statements.

if(x > max)
    max = x;

Disadvantages

Lack of inheritance capability

The primitive data types in languages such as Java cannot be inherited to create further subtypes as the wrapper classes like Integer, Float, etc are all final. Some applications that use OO languages might require more functionality than what is provided by the primitive datatype. For example, in Java, some of the composite data type like ArrayList, can be extended to add new functions like sum,etc to be used in the application.

public class MyArrayList<E> extends ArrayList<e> {
}

This provides a lot of customization options that help write more cleaner code. As an exception, the language SmallTalk allows even the basic primitive types to be inherited and modify the operations that can be performed on them.

Not Scalable

Using primitive datatypes is not scalable enough for real time applications. For example, a real time application would like to work with a large number of similar or varied type of data. To use primitive types for this scenario would involve creating a lot of variables and maintaining the state of all these variables, which is hard to do<ref>http://wiki.answers.com/Q/What_are_the_advantages_of_arrays_in_java arrays more scalable than primitive types</ref>. Composite objects like arrays or lists can provide easier representation and management of data. For example, to represent a list of variables,

char a[5] = {'c','a','d','f',h'}; 

Representing data in this way, allows easy access of the data as a[0], a[1], etc. This type of access by using a single variable to refer to multiple variables and memory locations allows performing similar operations on all the variables together (using loops or similar constructs).

Utility Functions

The presence of utility functions for composite objects allows a lot of operations to be performed on the data. For example in Java, the ArrayLists class allows any type of data to be stored in them and provides a lot of utility functions. Operations like searching within the list can be performed by simply calling a utility function available, where as the user would have had to write explicit functions had primitive types been used. The generic classes in Java donot allow primitive datatypes to be used as parameters. So, to use an ArrayList of integers in Java, we should use the wrapper class of int (Integer) instead.

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(5); // Though '5' is given as a primitive type, java performs Autoboxing to promote it to Integer Object.
list.add(4);
list.add(3);
list.add(2);
list.add(1);
System.out.println(list.contains(5));

Output:

true

In languages that do not support pointers, such collection objects also do not restrict the user from having a fixed number of entries<ref> http://stackoverflow.com/questions/4842883/are-there-reasons-to-prefer-arrays-over-arraylists ArrayLists better than Arrays </ref>. The number of entries in such a list can vary dynamically. Performing aggregate operations on a bunch of values is also much easier when composite objects are used. For example, Usage of the Collections framework present in Java allows to perform a lot of operations like sorting the values present in the collection. As the sort operations that are pre-implemented in the Collection framework are in-built java functions, they are extremely fast (order of nlog n).

Collections.sort(list);
System.out.println(list);

Output:

[1, 2, 3, 4, 5]

Exceptions to this are languages like Ruby, which treat all the basic types as objects and provide utility functions for all of them.

Null Values

Primitive data types do not allow to hold null values. So they cannot be used when a check for null value is essential<ref>http://stackoverflow.com/questions/2509025/when-to-use-primitive-and-when-reference-types-in-java When and when not to use primitives</ref>.

Unexpected results due to method overriding

There are certain examples such as this, which show that overriding inbuilt methods such as == and eql? can lead to unexpected results.

Conclusion

Primitive objects that are provided in object oriented programming languages have their own advantages and disadvantages. Though using primitive data types in most languages reduces the degree of customization possible, they provide a better performance and ease of use to compensate. The extent to which a primitive data type can be used efficiently depends on the application and the programming language used for the application.

References

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