- Defined in java.lang package.
- Primitive data type, although not implemented as objects, for performance considerations, their corresponding object representations are needed for the following reason:
There are collection classes that deal only with only objects. So, to store a primitive data type in one of these classes, we need to wrap the primitive type in a class.
- Thus, for all the 8 primitive data types in Java, equivalent Wrapper Classes are there.
Note that the class names start with capital letter. Except for Boolean & Character, all other classes are subclasses of an abstract class called 'Number'.
To build an object for a given primitive data type, all these classes have appropriate constructors defined. There are 2 types of constructors for all the classes except character.
1. Constructor — I
- Takes the corresponding type of numeric or boolean (for Boolean class) values as arguments and creates the object.
Double dd = new Doble(double);
Float ff = new Float(float);
Short ss = new Short(short);
Long ll = new Long(long);
Integer ii= new Integer(int);
Byte bb = new Byte(byte);
Boolean bool = new Boolean(boolean);
1. Integer I = new lnteger( 10);
Now 'i' is a reference to the object containing the integer value 10.
2. Double d 1 = new Double(10.41);
Double d2 = new Doublet 10.4);
3. Boolean bool = new Boolean(true);
2. Constructor - II
- It constructs the object from the string representation of a numeric data or boolean data.
Double dd new Doubler 110.5");
Long ll = new Long(" 1 50678924");
Byte bb = new Byte(args );
If "100" is given as the command line argument, which is in the form of a String, it can be converted to an object.