Primitive variable declaration doubts

[saloni jhanwar]

I've confusion, when i compile them there is no error so what is sense of these two versions of data types ,now java is sucking me
Can anyone tell differences between them ?

short x=7;
or
Short y=7;

Where are the rules ? ,it means i can use anything like that int or Int, char or Char ,Byte or byte, Double or double etc???

[Jelle Klap]

The first creates a primitive short with value 7.
The second creates a Short object, using auto-boxing to wrap the literal short value.
Before Java 5 the second appraoch would fail, and you would have to use the Short constructor that takes a primitive short.
As of Java 5 the second auto-boxing approach is equivalent to Short.valueOf(7) (this overload of valueOf was also added in Java 5).

[Anayonkar Shivalkar]

The difference is 'short' is a primitive data type whereas 'Short' is a class - which wraps primitive 'short'.

I'm not sure, but the only reason to (now) maintain primitive data types is backward compatibility and (perhaps) low memory footprint.

I hope this helps.

[saloni jhanwar]

Jelle Klap wrote:The first creates a primitive short with value 7.
The second creates a Short object, using auto-boxing to wrap the literal short value.
Before Java 5 the second appraoch would fail, and you would have to use the Short constructor that takes a primitive short.
As of Java 5 the second auto-boxing approach is equivalent to Short.valueOf(7) (this overload of valueOf was also added in Java 5).

Thanks Jelle but i m not getting this

Where are the rules ? ,it means i can use anything like that int or Int, char or Char ,Byte or byte, Double or double etc???

[Anayonkar Shivalkar]

Jelle Klap wrote:As of Java 5 the second auto-boxing approach is equivalent to Short.valueOf(7)

Is it so? I thought it is

Short y = new Short(7);

[saloni jhanwar]

Anayonkar Shivalkar wrote:The difference is 'short' is a primitive data type whereas 'Short' is a class - which wraps primitive 'short'.

I'm not sure, but the only reason to (now) maintain primitive data types is backward compatibility and (perhaps) low memory footprint.

I hope this helps.

Thanks Anayonkar if Short is class then what is short ? method or something else ?

[Anayonkar Shivalkar]

You are welcome.

saloni jhanwar wrote:if Short is class then what is short ? method or something else ?

No. Its just a primitive data type. A primitive data type is predefined by language and is treated as a reserved keyword.

On another note, wrapper class for int is Integer (not Int).

I hope this helps.

[saloni jhanwar]

Anayonkar Shivalkar wrote:You are welcome.

saloni jhanwar wrote:if Short is class then what is short ? method or something else ?

No. Its just a primitive data type. A primitive data type is predefined by language and is treated as a reserved keyword.

On another note, wrapper class for int is Integer (not Int).

I hope this helps.

Thanks, please tell me wrapper classes for other primitives also like for boolean,char,byte,double,float and long.

[Jelle Klap]

Anayonkar Shivalkar wrote:

Jelle Klap wrote:As of Java 5 the second auto-boxing approach is equivalent to Short.valueOf(7)

Is it so? I thought it is

Short y = new Short(7);

No boxing uses the valueOf() / xxxValue() pairs.
You can check this yourself using javap to dissasamble a .class file.
For instance:

public class Boxing {

  public static void main(String args[]) {
    Short boxedShort = 1;
    short unboxedShort =  boxedShort;
  }
}

Yields the following byte code using javap:

Compiled from "Boxing.java"
public class Boxing extends java.lang.Object{
public Boxing();
  Signature: ()V
  Code:
   0:	aload_0
   1:	invokespecial	#8; //Method java/lang/Object."<init>":()V
   4:	return

public static void main(java.lang.String[]);
  Signature: ([Ljava/lang/String;)V
  Code:
   0:	iconst_1
   1:	invokestatic	#16; //Method java/lang/Short.valueOf:(S)Ljava/lang/Short;
   4:	astore_1
   5:	aload_1
   6:	invokevirtual	#22; //Method java/lang/Short.shortValue:()S
   9:	istore_2
   10:	return
}

[Anayonkar Shivalkar]

Wrapper classes names are same as primitive data types - just first letter is capital (e.g. Boolean, Float).

Exceptions : Integer for int and Character for char.

[saloni jhanwar]

Anayonkar Shivalkar wrote:Wrapper classes names are same as primitive data types - just first letter is capital (e.g. Boolean, Float).

Exceptions : Integer for int and Character for char.

Thanks Anayonkar

[saloni jhanwar]

Wrapper class is a wrapper around a primitive data type. It represents primitive data types in their corresponding class instances e.g. a boolean data type can be represented as a Boolean class instance. All of the primitive wrapper classes in Java are immutable i.e. once assigned a value to a wrapper class instance cannot be changed further.

Following table lists the primitive types and the corresponding wrapper classes:

Primitive Wrapper
---------------------------------
boolean java.lang.Boolean
byte java.lang.Byte
char java.lang.Character
double java.lang.Double
float java.lang.Float
int java.lang.Integer
long java.lang.Long
short java.lang.Short
void java.lang.Void

[Anayonkar Shivalkar]

Jelle Klap wrote:boxing uses the valueOf() / xxxValue() pairs.
You can check this yourself using javap to dissasamble a .class file.

Thank you (I should've checked it btw)