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Each primitive type has a wrapper class, which is an object type that corresponds to the primitive. Table 1.7 lists all the wrapper classes along with how to create them.

TABLE 1.7 Wrapper classes

Primitive type	Wrapper class	Wrapper class inherits Number?	Example of creating
boolean	Boolean	No	Boolean.valueOf(true)
byte	Byte	Yes	Byte.valueOf((byte) 1)
short	Short	Yes	Short.valueOf((short) 1)
int	Integer	Yes	Integer.valueOf(1)
long	Long	Yes	Long.valueOf(1)
float	Float	Yes	Float.valueOf((float) 1.0)
double	Double	Yes	Double.valueOf(1.0)
char	Character	No	Character.valueOf('c')

There is also a valueOf() variant that converts a String into the wrapper class. For example:

int primitive = Integer.parseInt("123"); Integer wrapper = Integer.valueOf("123");

The first line converts a String to an int primitive. The second converts a String to an Integer wrapper class.

All of the numeric classes in Table 1.7 extend the Number class, which means they all come with some useful helper methods: byteValue(), shortValue(), intValue(), longValue(), floatValue(), and doubleValue(). The Boolean and Character wrapper classes include booleanValue() and charValue(), respectively.

As you probably guessed, these methods return the primitive value of a wrapper instance, in the type requested.

Double apple = Double.valueOf("200.99"); System.out.println(apple.byteValue()); // -56 System.out.println(apple.intValue()); // 200 System.out.println(apple.doubleValue()); // 200.99

These helper methods do their best to convert values but can result in a loss of precision. In the first example, there is no 200 in byte, so it wraps around to -56. In the second example, the value is truncated, which means all of the numbers after the decimal are dropped. In Chapter 5, we apply autoboxing and unboxing to show how easy Java makes it to work with primitive and wrapper values.

Some of the wrapper classes contain additional helper methods for working with numbers. You don't need to memorize these; you can assume any you are given are valid. For example, Integer has:

 max(int num1, int num2), which returns the largest of the two numbers

 min(int num1, int num2), which returns the smallest of the two numbers

 sum(int num1, int num2), which adds the two numbers