GRAPHICAL USER INTERFACE (GUI) AND OBJECT-ORIENTED DESIGN (OOD) - Java Programming: From Problem Analysis to Program Design - page 372

TABLE 6-6 Some Members of the class Integer (continued)

public static int parseInt(String str)
//Returns the value of the number contained in str.

public String toString()
//Returns the int value, of the object, as a string.

public static String toString( int num)
//Returns the value of num as a string.

public static Integer valueOf(String str)
//Returns an Integer object initialized to the value
//specified by str.

The wrapper classes are contained in the package java.lang. As noted in Chapter 2, if
a class is contained in the package java.lang, to use that class in a program, it is not necessary
to explicitly import that class using the import statement. The system automatically imports
classes contained in the package java.lang. Therefore, to use the class Integer in a
program, it is not necessary to explicitly import this class using the import statement.

Consider the following statements:

Integer num; //Line 1

num = new Integer(86) //Line 2

The statement in Line 1 declares num to be a reference variable of type Integer .The
statement in Line 2 creates an Integer object, stores the value 86 in it, and then stores
the address of this object into num . (See Figure 6-16. Suppose that the address of the
Integer object is 1350 .)

1350

num 1350 86

FIGURE 6-16 The reference variable num and the object it points to

As you can see, the int value 86 is wrapped into an Integer object. Just like the class
String , the class Integer does not provide any method to change the value of an
existing Integer object. That is, Integer objects are immutable. (In fact, wrapper
class objects are immutable.)