7.6 Type Declarations

A type declaration declares a class type (§8) or an interface type (§9):

TypeDeclaration:

	ClassDeclaration

	InterfaceDeclaration

	;

A Java compiler must ignore extra ";" tokens appearing at the level of type declarations. Stray semicolons are permitted in Java solely as a concession to C++ programmers who are used to writing:

class date { int month, day, year; };

(In C++, but not in Java, one can provide a comma-separated list of identifiers in order to declare variables between the "}" and the ";".) Extra semicolons should not be used in new Java code. Software that reformats Java code can delete them.

By default, the types declared in a package are accessible only within the compilation units of that package, but a type may be declared to be public to grant access to the type from code in other packages (§6.6, §8.1.2, §9.1.2).

A Java implementation must keep track of types within packages by their fully qualified names (§6.7). Multiple ways of naming a type must be expanded to fully qualified names to make sure that such names are understood as referring to the same type. For example, if a compilation unit contains the single-type-import declaration (§7.5.1):

import java.util.Vector;

then within that compilation unit the simple name Vector and the fully qualified name java.util.Vector refer to the same type.

When Java packages are stored in a file system (§7.2.1), the host system may choose to enforce the restriction that it is a compile-time error if a type is not found in a file under a name composed of the type name plus an extension (such as .java or .jav) if either of the following is true:

• The type is referred to by code in other compilation units of the package in which the type is declared.
• The type is declared public (and therefore is potentially accessible from code in other packages).

This restriction implies that there must be at most one such type per compilation unit. This restriction makes it easy for a Java compiler and Java Virtual Machine to find a named class within a package; for example, the source code for a public type wet.sprocket.Toad would be found in a file Toad.java in the directory wet/sprocket, and the corresponding object code would be found in the file Toad.class in the same directory.

When Java packages are stored in a database (§7.2.2), the host system need not enforce such restrictions.

In practice, many Java programmers choose to put each class or interface type in its own compilation unit, whether or not it is public or is referred to by code in other compilation units.