Java File Structure
This chapter has taken us from the smallest to the largest elements of Java syntax, from individual characters and tokens to operators, expressions, statements, and methods, and on up to classes and packages. From a practical standpoint, the unit of Java program structure you will be dealing with most often is the Java file. A Java file is the smallest unit of Java code that can be compiled by the Java compiler. A Java file consists of:
Zero or more
One or more type definitions
These elements can be interspersed with comments, of course, but they
must appear in this order. This is all there is to a Java file. All
Java statements (except the
import directives, which are not true statements)
must appear within methods, and all methods must appear within a type
Java files have a couple of other
important restrictions. First, each file can contain at most one
class that is declared
public class is one that is designed for use by
other classes in other packages. This restriction on public classes
only applies to top-level classes; a class can contain any number of
nested or inner classes that are declared
We’ll see more about the
modifier and nested classes in Chapter 3.
second restriction concerns the filename of a Java file. If a Java
file contains a
public class, the name of the file must be the same as the name of the class, with the extension ...
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