W

widening conversion

What happens when a value of one type is converted to a wider type—that is, a type with a wider range of possible values. Converting from a short to an int is a widening conversion; converting from a char to a byte is not. The Java runtime knows that your variable couldn't suffer any loss of data by putting its value in a container bigger than the one it already has. For this reason, widening conversions happen automatically. You can lose data when performing a widening conversion that is done automatically. Numerical range is the important thing. Example (float's numerical range encompasses long's, but long (64-bits) can hold more digits than float (32-bits)):

public class ConversionTest {
public static void main(String[] args) {
     float a;
     long b = 4203020102023324L;
     a = b;
     System.out.println("float: " + a);
     System.out.println("long: " + b);
     }}

Output:

float: 4.2030201E15
long: 4203020102023324

wildcard

Used in regular expressions to mean any character. In generics, the wildcard is represented as ?. This is used in a generic method declaration to indicate an unknown type. The wildcard can be type-bounded by either upper or lower limits.

See also [bounds]

wrapper class

The primitive wrapper classes in the java.lang package correspond to each of the eight primitive variable types: the Boolean primitive wrapper class is java.lang.Boolean; the char wrapper class is Character, and so forth. The purpose of the primitive wrappers is to provide utility methods (such as Double.parseDouble()), constants (such as Boolean.TRUE and Float.POSITIVE_INFINITY), and object encapsulation for primitives.