Programming and Problem Solving with Java

2.1 The Elements of Java Programs | 49

Notice that each character is enclosed in single quotes (apostrophes). The Java compiler
needs the quotes to be able to differentiate between the character data and other Java ele-
ments. For example, the quotes around the characters ‘A‘and ‘+‘distinguish them from the
identifier Aand the addition sign. Notice also that the blank,‘ ‘, is a valid character.
How do we write the single quote itself as a character? If we write ‘‘‘, Java complains
that we have made a syntax error. The second quote indicates the end of the (empty) char-
acter value, and the third quote starts a new character value. To deal with this problem, Java
provides a special escape sequencethat allows us to write a single quote as a character. That

Data Storage

Where does our code get the data it needs to operate? Data is stored in the computer’s memory.

Recall that memory is divided into a large number of separate locations or cells, each of which

can hold a piece of data. Each memory location has a unique address we refer to when we store

or retrieve data. We can visualize memory as a set of post office boxes, with the box numbers

serving as the addresses used to designate particular locations.

Of course, the actual address of each location in memory is a binary number in a machine

language code. In Java, we use identifiers to name memory locations; the compiler and the JVM

then translate those identifiers into binary form for us. This translation represents one of the

advantages provided by a high-level programming language: It frees us from having to keep

track of the numeric addresses of the memory locations in which our data and instructions are

stored.

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