Java is an object
oriented language and java treats everything as an object. For example, A
simple file (java.io.File), a Calendar (java.util.Calendar), a date
(java.util.Date), an image (java.awt.Image), a color (java.awt.Color)
are represented by the classes and their objects. Primitive data types
like int, float, double, boolean, char etc. are also represented by the
classes called Wrapper Claases. For every primitive data type, there is a Wrapper Class in java. All wrapper classes are placed in java.lang package. Below is the list of primitive data types and their corresponding wrapper classes.
| Primitive Data Type | Corresponding Wrapper Class |
| byte | java.lang.Byte |
| short | java.lang.Short |
| int | java.lang.Integer |
| long | java.lang.Long |
| float | java.lang.Float |
| double | java.lang.Double |
| boolean | java.lang.Boolean |
| char | java.lang.Character |
Wrapper
classes are mainly used to wrap the primitive content into an object.
This operation of wrapping primitive content into an object is called boxing. The reverse process i.e unwrapping the object into corresponding primitive data is called Unboxing.
Boxing :
Following example shows the boxing i.e wrapping primitive content into corresponding wrapper object.
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| public class WrapperClasses{ public static void main(String[] args) { byte b = 10; //Primitive byte data Byte B = new Byte(b); //Wrapping primitive byte data into Byte Object short s = 15; //Primitive short data Short S = new Short(s); //Wrapping of short data into Short Object int i = 20; //Primitive int Data Integer I = new Integer(i); //Wrapping of int data into Integer Object long l = 25; //Primitive long data Long L = new Long(l); //Wrapping primitive long data into Long Object float f = 12.5F; //Primitive float data Float F = new Float(f); //Wrapping float data into Float Object double d = 18.58; //Primitive double data Double D = new Double(d); //Wrapping double data into Double Object boolean bln = true; //Primitive boolean data Boolean BLN = new Boolean(bln); //Wrapping boolean into Boolean Object char c = 'C'; //Primitive char data Character C = new Character(c); //Wrapping char into Character Object }} |
Auto-Boxing :
From JDK 1.5 onwards,
Auto-Boxing is introduced. According to this feature, you need not to
explicitly wrap the primitive content into an object. Just assign
primiive data to corresponding wrapper class reference variable,
java automatically wraps primitive data into corresponding wrapper
object.
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| public class WrapperClasses{ public static void main(String[] args) { byte b = 10; //Primitive byte data Byte B = b; //Auto-Boxing of byte data short s = 15; //Primitive short data Short S = s; //Auto-Boxing of short data int i = 20; //Primitive int Data Integer I = i; //Auto-Boxing of int data long l = 25; //Primitive long data Long L = l; //Auto-Boxing of long data float f = 12; //Primitive float data Float F = f; //Auto-Boxing of float data double d = 18.58; //Primitive double data Double D = d; //Auto-Boxing of double data boolean bln = true; //Primitive boolean data Boolean BLN = bln; //Auto-Boxing of boolean data char c = 'C'; //Primitive char data Character C = c; //Auto-Boxing of char data }} |
Unboxing :
All wrapper classes
have methods to unwrap the object to corresponding primitive data. Go
through the following example, it shows unboxing i.e unwrapping wrapper
object into corresponding primitive data.
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| public class WrapperClasses{ public static void main(String[] args) { Byte B = new Byte((byte) 10); //Byte Object byte b = B.byteValue(); //Unwrapping Byte object to byte data Short S = new Short((short) 20); //Short Object short s = S.shortValue(); //Unwrapping Short object to short data Integer I = new Integer(15); //Integer Object int i = I.intValue(); //Unwrapping Integer object to int data Long L = new Long(50); //Long Object long l = L.longValue(); //Unwrapping Long object to long data Float F = new Float(20); //Float Object float f = F.floatValue(); //Unwrapping Float object to float data Double D = new Double(20.5); //Double Object double d = D.doubleValue(); //Unwrapping Double object to double data Boolean BLN = new Boolean(true); //Boolean Object boolean bln = BLN.booleanValue(); //Unwrap Boolean obj to boolean data Character C = new Character('C'); //Character Object char c = C.charValue(); //Unwrapping Character object to char data }} |
Auto-Unboxing :
From JDK 1.5 onwards,
Auto-Unboxing is introduced. According to this feature, you need not to
call method of wrapper class to unbox the wrapper object. Java
implicitly converts wrapper object to corresponding primitive data if
you assign wrapper object to primitive type variable.
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| public class WrapperClasses{ public static void main(String[] args) { Byte B = new Byte((byte) 10); //Byte Object byte b = B; //Auto-Unboxing of Byte Object Short S = new Short((short) 20); //Short Object short s = S; //Auto-Unboxing of Short Object Integer I = new Integer(15); //Integer Object int i = I; //Auto-Unboxing of Integer Object Long L = new Long(50); //Long Object long l = L; //Auto-Unboxing of Long Object Float F = new Float(20); //Float Object float f = F; //Auto-Unboxing of Float Object Double D = new Double(20.5); //Double Object double d = D; //Auto-Unboxing of Double Object Boolean BLN = new Boolean(true); //Boolean Object boolean bln = BLN; //Auto-Unboxing of Boolean Object Character C = new Character('C'); //Character Object char c = C; //Auto-Unboxing of Character Object }} |
That’s it for today.
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