Java: Wrapper Classes

This tech recipe describes going to and from the Java Object wrapper classes.

Wrapper classes do exactly what the name implies: they wrap primitive types (e.g., int, double, etc.) in Objects which can be placed into Vectors, and 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 Objects.

These Wrapper classes can be created in many ways, so I will start slowly by 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.

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

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

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

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:

int i = Integer.parseInt(“234”);

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

float f = Float.parseFloat(“234.78”);

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: [email protected]
-William. § (marvin_gohan)




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