Java Reference
In-Depth Information
Self-Test Exercises
4. What is a compiler?
5. What is a source program?
6. What is an object program?
7. What do you call a program that runs Java byte-code instructions?
8. Suppose you define a class named
NiceClass
in a file. What name should the file
have?
9. Suppose you compile the class
NiceClass
. What will be the name of the file with
the resulting byte-code?
1.2
Expressions and Assignment Statements
Once a person has understood the way variables are used in program-
ming, he has understood the quintessence of programming.
E. W. DIJKSTRA, Notes on Structured Programming
Variables, expressions, and assignments in Java are similar to their counterparts in
most other general-purpose languages. In this section we describe the details.
Identifiers
The name of a variable (or other item you might define in a program) is called an
identifier
. A Java identifier must not start with a digit and all the characters must be
letters, digits, or the underscore symbol. (The symbol $ is also allowed, but it is
reserved for special purposes, and so you should not use $ in your Java identifiers.) For
example, the following are all valid identifiers:
identifier
x x1 x_1 _abc ABC123z7 sum RATE count data2 bigBonus
All of the preceding names are legal and would be accepted by the compiler, but the first
five are poor choices for identifiers, since they are not descriptive of the identifier's use.
None of the following are legal identifiers and all would be rejected by the compiler:
12 3X %change data-1 myfirst.java PROG.CLASS
The first two are not allowed because they start with a digit. The remaining four are
not identifiers because they contain symbols other than letters, digits, and the under-
score symbol.
