8.1 Class Declaration

A class declaration specifies a new reference type:

ClassDeclaration:

	ClassModifiersopt class Identifier Superopt Interfacesopt ClassBody

If a class is declared in a named package (§7.4.1) with fully qualified name P (§6.7), then the class has the fully qualified name P.Identifier. If the class is in an unnamed package (§7.4.2), then the class has the fully qualified name Identifier. In the example:

class Point { int x, y; }

the class Point is declared in a compilation unit with no package statement, and thus Point is its fully qualified name, whereas in the example:

package vista;
class Point { int x, y; }

the fully qualified name of the class Point is vista.Point. (The package name vista is suitable for local or personal use; if the package were intended to be widely distributed, it would be better to give it a unique package name (§7.7).)

A compile-time error occurs if the Identifier naming a class appears as the name of any other class type or interface type declared in the same package (§7.6).

A compile-time error occurs if the Identifier naming a class is also declared as a type by a single-type-import declaration (§7.5.1) in the compilation unit (§7.3) containing the class declaration.

In the example:

package test;

import java.util.Vector;


class Point {
	int x, y;
}


interface Point {											// compile-time error #1
	int getR();
	int getTheta();
}

class Vector { Point[] pts; }											// compile-time error #2

the first compile-time error is caused by the duplicate declaration of the name Point as both a class and an interface in the same package. A second error detected at compile time is the attempt to declare the name Vector both by a class type declaration and by a single-type-import declaration.

Note, however, that it is not an error for the Identifier that names a class also to name a type that otherwise might be imported by a type-import-on-demand declaration (§7.5.2) in the compilation unit (§7.3) containing the class declaration. In the example:

package test;

import java.util.*;

class Vector { Point[] pts; }											// not a compile-time error

the declaration of the class Vector is permitted even though there is also a class java.util.Vector. Within this compilation unit, the simple name Vector refers to the class test.Vector, not to java.util.Vector (which can still be referred to by code within the compilation unit, but only by its fully qualified name).