15.9.5 Anonymous Class Declarations

EXPRESSIONS

The value of a class instance creation expression is a reference to the newly created object of the specified class. Every time the expression is evaluated, a fresh object is created.

Example 15.9.4-1. Evaluation Order and Out-Of-Memory Detection

If evaluation of a class instance creation expression finds there is insufficient memory to perform the creation operation, then an OutOfMemoryError is thrown. This check occurs before any argument expressions are evaluated.

So, for example, the test program:

class List { int value; List next;

static List head = new List(0);

List(int n) { value = n; next = head; head = this; }

}

class Test {

public static void main(String[] args) { int id = 0, oldid = 0;

try {

for (;;) { ++id;

new List(oldid = id);

}

} catch (Error e) { List.head = null;

System.out.println(e.getClass() + ", " + (oldid==id));

}

}

}

prints:

class java.lang.OutOfMemoryError, false

because the out-of-memory condition is detected before the argument expression oldid = id is evaluated.

Compare this to the treatment of array creation expressions (§15.10), for which the out-of- memory condition is detected after evaluation of the dimension expressions (§15.10.1).

15.9.5 Anonymous Class Declarations

An anonymous class declaration is automatically derived from a class instance creation expression by the Java compiler.

An anonymous class is never abstract (§8.1.1.1).

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EXPRESSIONS

Anonymous Class Declarations 15.9.5

An anonymous class is always implicitly final (§8.1.1.2).

An anonymous class is always an inner class (§8.1.3); it is never static (§8.1.1, §8.5.1).

15.9.5.1 Anonymous Constructors

An anonymous class cannot have an explicitly declared constructor. Instead, a Java compiler must automatically provide an anonymous constructor for the anonymous class. The form of the anonymous constructor of an anonymous class C with direct superclass S is as follows:

•If S is not an inner class, or if S is a local class that occurs in a static context, then the anonymous constructor has one formal parameter for each actual argument to the class instance creation expression in which C is declared.

The actual arguments to the class instance creation expression are used to determine a constructor cs of S, using the same rules as for method invocations (§15.12).

The type of each formal parameter of the anonymous constructor must be identical to the corresponding formal parameter of cs.

The body of the constructor consists of an explicit constructor invocation (§8.8.7.1) of the form super(...), where the actual arguments are the formal parameters of the constructor, in the order they were declared.

•Otherwise, the first formal parameter of the constructor of C represents the value of the immediately enclosing instance of i with respect to S. The type of this parameter is the class type that immediately encloses the declaration of S.

The constructor has an additional formal parameter for each actual argument to the class instance creation expression that declared the anonymous class. The n'th formal parameter e corresponds to the n-1'th actual argument.

The actual arguments to the class instance creation expression are used to determine a constructor cs of S, using the same rules as for method invocations (§15.12).

The type of each formal parameter of the anonymous constructor must be identical to the corresponding formal parameter of cs.

The body of the constructor consists of an explicit constructor invocation (§8.8.7.1) of the form o.super(...), where o is the first formal parameter of the constructor, and the actual arguments are the subsequent formal parameters of the constructor, in the order they were declared.

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