Learning Java

Statements and Expressions

Although the method declaration syntax of Java is quite different from that of C++, Java statement and expression syntax is like that of C. Again, the intention was to make the low-level details of Java easily accessible to C programmers, so that they can concentrate on learning the parts of the language that are really different. Java statements appear inside of methods and classes; they describe all activities of a Java program. Variable declarations and assignments, such as those in the previous section, are statements, as are the basic language structures like conditionals and loops. Expressions describe values; an expression is evaluated to produce a result, to be used as part of another expression or in a statement. Method calls, object allocations, and, of course, mathematical expressions are examples of expressions. Technically, since variable assignments can be used as values for further assignments or operations (in somewhat questionable programming style), they can be considered to be both statements and expressions.

One of the tenets of Java is to keep things simple and consistent. To that end, when there are no other constraints, evaluations and initializations in Java always occur in the order in which they appear in the code—from left to right. We’ll see this rule used in the evaluation of assignment expressions, method calls, and array indexes, to name a few cases. In some other languages, the order of evaluation is more complicated or ...