Java Reference
In-Depth Information
Chapter 2 introduced you to the basic elements of Java programs, including special
symbols and identifiers, primitive data types, arithmetic operators, and the order of
precedence of arithmetic operators. You were briefly introduced to the class String
for processing strings, the class Scanner for inputting data into a program, and general
rules on programming style. In this chapter, you will learn more about input and output
and how to use predefined methods in your programs. You will also learn, in some detail,
how to use the class String to process strings.
Objects and Reference Variables
Three terms that you will encounter repeatedly throughout this topic are variables, reference
variables, and objects. We define these terms now so you will be familiar with them.
In Chapter 2, you learned about the primitive data types, such as int , double ,and char .
You also worked with strings. We used String variables to manipulate or process strings.
Consider the following statement:
int x; //Line 1
This statement declares x to be an int variable. Now consider the statement:
String str;
//Line 2
This statement declares str to be a variable of type String .
The statement in Line 1 allocates memory space to store an int value and calls this
memory space x . The variable x can store an int value in its memory space. For example,
the following statement stores 45 in x , as shown in Figure 3-1:
x = 45;
//Line 3
x
45
FIGURE 3-1 Variable x and its data
Next, let us see what happens with the statement in Line 2. This statement allocates
memory space for the variable str . However, unlike the variable x , the variable str
cannot directly store data in its memory space. The variable str stores the memory
location, that is, the address of the memory space where the actual data is stored. For
example, the effect of the statement:
str = "Java Programming";
//Line 4
is shown in Figure 3-2.
 
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