2.4 Wrapper Classes

Java's integer types are called primitive types because their values are not objects. A primitive value does not have fields that maintain its state, nor does it have methods that manipulate the value. On the other hand, a reference type can be a class or an array type. Its values are objects, which are instances of the class or array type. In a Java program, a variable whose type is a primitive type represents a value of that type. A variable whose type is a reference type represents a pointer to an object of that type.

Java provides a wrapper class for each of the primitive integer types, named Byte, Short, Character, Integer, and Long. These are class names , not keywords.

A wrapper class's constructor creates a wrapper object for a primitive type's value. For example, new Integer(3) wraps the int value 3 in an object.

The wrapper classes contain useful methods and constant fields. Each one has a MIN_VALUE and a MAX_VALUE constant, which represents the minimum value and the maximum value, respectively, of the corresponding primitive type. Classes Integer and Long have a toBinary String() method and a toHexString() method, which return string representations of an integer value as an unsigned binary and an unsigned hexadecimal number, respectively.

Program 2 C2 demonstrates some of the features of the wrapper classes. See Listing 2-2.

Listing 2-2 The integer wrapper classes.

package numbercruncher.program2_2;

/**
 * PROGRAM 2-2: Integer Wrapper Classes
 *
 * Print the values of some of the constants
 * defined in the integer wrapper classes.
 */
public class IntegerWrapperClasses
{
    public static void main(String args[])
    {
        // Byte
        System.out.println("Byte.MIN_VALUE = " + Byte.MIN_VALUE);
        System.out.println("Byte.MAX_VALUE = " + Byte.MAX_VALUE);
        System.out.println();

        // Short
        System.out.println("Short.MIN_VALUE = " + Short.MIN_VALUE);
        System.out.println("Short.MAX_VALUE = " + Short.MAX_VALUE);
        System.out.println();

        // Character
        System.out.println("Character.MIN_VALUE = " +
                           (int) Character.MIN_VALUE);
        System.out.println("Character.MAX_VALUE = " +
                           (int) Character.MAX_VALUE);
        System.out.println();

        // Integer
        System.out.println("Integer.MIN_VALUE = " + Integer.MIN_VALUE);
        System.out.println("Binary: " +
                           Integer.toBinaryString(Integer.MIN_VALUE));
        System.out.println("   Hex: " +
                           Integer.toHexString(Integer.MIN_VALUE));
        System.out.println();
        System.out.println("Integer.MAX_VALUE = " + Integer.MAX_VALUE);
        System.out.println("Binary: " +
                           Integer.toBinaryString(Integer.MAX_VALUE));
        System.out.println("   Hex: " +
                           Integer.toHexString(Integer.MAX_VALUE));
        System.out.println();

        // Long
        System.out.println("Long.MIN_VALUE = " + Long.MIN_VALUE);
        System.out.println("Binary: " +
                           Long.toBinaryString(Long.MIN_VALUE));
        System.out.println("   Hex: " +
                           Long.toHexString(Long.MIN_VALUE));
        System.out.println();
        System.out.println("Long.MAX_VALUE = " + Long.MAX_VALUE);
        System.out.println("Binary: " +
                           Long.toBinaryString(Long.MAX_VALUE));
        System.out.println("   Hex: " +
                           Long.toHexString(Long.MAX_VALUE));
    }
}

Output:

Byte.MIN_VALUE = -128
Byte.MAX_VALUE = 127

Short.MIN_VALUE = -32768
Short.MAX_VALUE = 32767

Character.MIN_VALUE = 0
Character.MAX_VALUE = 65535

Integer.MIN_VALUE = -2147483648
Binary: 10000000000000000000000000000000
   Hex: 80000000

Integer.MAX_VALUE = 2147483647
Binary: 1111111111111111111111111111111
   Hex: 7fffffff

Long.MIN_VALUE = -9223372036854775808
Binary: 1000000000000000000000000000000000000000000000000000000000000000
   Hex: 8000000000000000

Long.MAX_VALUE = 9223372036854775807
Binary: 111111111111111111111111111111111111111111111111111111111111111
   Hex: 7fffffffffffffff