Java: Wrapper Classes

Contributed by William_Wilson  
Tagged: Java programming  

Decription on going to and from the java Object wrapper classes.

Wrapper classes to exactly what they say, they wrap primitive types (eg: int, double, etc) in Objects which can be placed into Vectors, and many, many other uses.

*Notice that an Object starts with a capital letter, while the primitives all start with a lowercase. Also notice that Strings are Ojects.

These Wrapper classes can be created in many ways, so i will start slow, simply returning objects with a String.

Integer from String:
Integer i = Integer.valueOf(“125″);

Double from String:
Double d = Double.valueOf(“5.829754097″);

Float from String:
Float f = Float.valueOf(“8.43543″);

Boolean from String:
Boolen b = Boolean.valueOf(“true”);
//This will represent true

Character from String:
Character c = Character.valueOf(“G”);

The more common use is given the primitive in a variable. This next section shows how to convert a variable to these wrapper classes and back to a primitive.

Integer:
int i = 5;
Integer I = Integer.valueOf(i); //Wrapper
int i2 = I.intValue(); //back to primitive

Float:
float f = 5.5f;
Float F = Float.valueOf(f); //Wrapper
float f2 = F.floatValue(); //back to primitive

Double:
double d = 5.55555;
Double D = Double.valueOf(d); //Wrapper
double d2 = D.doubleValue(); //back to primitive

Boolean:
boolean b = true;
Boolean B = Boolean.valueOf(b); //Wrapper
boolean b2 = B.booleanValue(); //back to primitive

*When dealing with strings you may also wish to use the following to get primitives from the Object String:

Integer:
int i = Integer.parseInt(“234″);

Double
double d = Double.parseDouble(“234.6576533254″);

Float:
float f = Float.parseFloat(“234.78″);

Long:
long l = Long.parseLong(“23454654″);

*Note you may wish to add the ().trim feature to these last ones, in the case of extra white space around your String, which may cause exceptions.
Example of trim:
String s = ” William “; // displays as ‘ William ‘
String s2 = (s).trim(); //displays ‘William’

Questions/Comments: william_a_wilson@hotmail.com
-William. § (marvin_gohan)