Programming and Problem Solving with Java

2.1 The Elements of Java Programs | 63

assigns the string “The square of 12 is 144”to the variable result. Java converts the integer
literal 144 into the string “ 144 ”before performing the concatenation.

Initializer Expressions Now that we have defined expressions, we can generalize the field dec-

laration syntax to allow for the use of an expression in initializing the field.

The following declarations are, therefore, legal:

finalString WORD1 = “Introduction”;
finalString WORD3 = “Java “+ WORD1;
finalString WORD5 = “Design “+ WORD3;

They store “Design Java Introduction”as the value of the constantWORD5.

Modifiers Type-Name Identifier = Expression

Field-Declaration

, Identifier = Expression ;

Assignment of Primitive Types Versus Objects

After reading the preceding discussion of assignment statements and expressions, you may

wonder what really happens inside the computer when assignment occurs. For Java’s primitive

types that represent simple data values such as characters and numbers, the answer is

straightforward: The value on the right side of the equals sign is stored in the memory location

corresponding to the identifier on the left-hand side.

But what about objects such as strings? Surely they can’t fit into a single memory location?

The answer is no, they can’t. So how does assignment work in that case?

Assignment of objects is done indirectly. A variable of the object data type contains a value

that is the memory address where the actual object is stored. When Java needs to operate on an

object, it uses the value stored in the variable to find the object in memory. This process takes

place automatically, so we don’t have to worry about it. With respect to assignment, however, it

means that assigning one object variable to another works just the same as assigning one inte-

ger variable to another. The value contained in one variable is copied from its memory location

into the location associated with the other variable. For an object, this value is an address in

memory.

In later chapters we will return to this topic and note that it has some additional

consequences. In the meantime, we will avoid situations where this issue might cause

problems.