Package com.thoughtworks.proxy.toys.nullobject

A toy to create dummy null objects with intelligent behaviour.

See: Description

Class Summary

Class	Description
Null	Toy factory to create proxies acting as Null Objects.
NullInvoker	A Invoker implementation that returns always new Null objects.

Package com.thoughtworks.proxy.toys.nullobject Description

A toy to create dummy null objects with intelligent behaviour.

The package provides a proxy factory creating proxies, that work as a dummy replacement. Main component is the Null toy, a utility class creating these proxies. Such a proxy contains an instance of a NullInvoker that handles the calls.

A null object instantiated by this toy has deterministically boring behaviour as follows:

• If a method's return type is a primitive, the null object returns the default for that type (e.g. false for boolean).
• If a method's return type is an array, the null object returns an empty array, which is usually nicer than just returning null. (In fact an empty array is just the null object for arrays.)
• If a method's return type is List, Collections.EMPTY_LIST is returned.
• If a method's return type is Set, Collections.EMPTY_SET is returned.
• If a method's return type is Map, Collections.EMPTY_MAP is returned.
• If a method's return type is SortedSet, Null.NULL_SORTED_SET is returned.
• If a method's return type is SortedMap, Null.NULL_SORTED_MAP is returned.
• If a method's return type is Object, an Object is returned.
• If the method's return type is any other type, the Null toy returns one of the following:
• If the currently installed ProxyFactory can create a proxy for the type, a new null object for that type is returned (so you can recurse or step through object graphs without surprises). For the standard proxy factory this requires the return type to be an interface.
• If the ProxyFactory in use cannot create a proxy for the type, null is returned.

In the follwoing example the behaviour is demonstrated by an Null object of the type File:

ProxyFactory factory = new CglibProxyFactory();
File file = (File)Null.object(File.class, factory);
System.out.println("Length is: " + file.length());
System.out.println("Exists: " + file.exists());
System.out.println("Array is empty: " + file.list().length);
System.out.println("toURL returns null, since URL is final: " + (file.toURL() == null));
System.out.println("Parent file is Null proxy: " + Null.isNullObject(file.getParentFile(), factory));