PropertyDescriptor (GNU Classpath 0.94-pre Documentation)

PropertyDescriptor describes information about a JavaBean property, by which we mean a property that has been exposed via a pair of get and set methods. (There may be no get method, which means the property is write-only, or no set method, which means the the property is read-only.)

The constraints put on get and set methods are:

A get method must have signature <propertyType> <getMethodName>()
A set method must have signature void <setMethodName>(<propertyType>)
Either method type may throw any exception.
Both methods must be public.

Since: 1.1

UNKNOWN: updated to 1.4

Constructor Summary
	PropertyDescriptor(String name, Class<?> beanClass) Create a new PropertyDescriptor by introspection.
	PropertyDescriptor(String name, Class<?> beanClass, String getMethodName, String setMethodName) Create a new PropertyDescriptor by introspection.
	PropertyDescriptor(String name, Method readMethod, Method writeMethod) Create a new PropertyDescriptor using explicit Methods.

Method Summary
PropertyEditor	createPropertyEditor(Object bean) Instantiate a property editor using the property editor class.
boolean	equals(Object o) Compares this `PropertyDescriptor` against the given object.
Class<?>	getPropertyEditorClass() Get the PropertyEditor class.
Class<?>	getPropertyType() Get the property type.
Method	getReadMethod() Get the get method.
Method	getWriteMethod() Get the set method.
int	hashCode() Return a hash code for this object, conforming to the contract described in {@link Object#hashCode()}.
boolean	isBound() Get whether the property is bound.
boolean	isConstrained() Get whether the property is constrained.
void	setBound(boolean bound) Set whether the property is bound.
void	setConstrained(boolean constrained) Set whether the property is constrained.
void	setPropertyEditorClass(Class<?> propertyEditorClass) Set the PropertyEditor class.
void	setReadMethod(Method readMethod) Sets the read method. The read method is used to retrieve the value of a property.
void	setWriteMethod(Method writeMethod) Sets the write method. The write method is used to set the value of a property.

Constructor Detail

PropertyDescriptor

Create a new PropertyDescriptor by introspection. This form of constructor creates the PropertyDescriptor by looking for a getter method named get<name>() (or, optionally, if the property is boolean, is<name>()) and set<name>() in class <beanClass>, where <name> has its first letter capitalized by the constructor.

Note that using this constructor the given property must be read- and writeable. If the implementation does not both, a read and a write method, an IntrospectionException is thrown. Implementation note: If there is both are both isXXX and getXXX methods, the former is used in preference to the latter. We do not check that an isXXX method returns a boolean. In both cases, this matches the behaviour of JDK 1.4

Parameters: name the programmatic name of the property, usually starting with a lowercase letter (e.g. fooManChu instead of FooManChu). beanClass the class the get and set methods live in.

Throws: IntrospectionException if the methods are not found or invalid.

PropertyDescriptor

Create a new PropertyDescriptor by introspection. This form of constructor allows you to specify the names of the get and set methods to search for.

Implementation note: If there is a get method (or boolean isXXX() method), then the return type of that method is used to find the set method. If there is no get method, then the set method is searched for exhaustively.

Spec note: If there is no get method and multiple set methods with the same name and a single parameter (different type of course), then an IntrospectionException is thrown. While Sun's spec does not state this, it can make Bean behavior different on different systems (since method order is not guaranteed) and as such, can be treated as a bug in the spec. I am not aware of whether Sun's implementation catches this.

Parameters: name the programmatic name of the property, usually starting with a lowercase letter (e.g. fooManChu instead of FooManChu). beanClass the class the get and set methods live in. getMethodName the name of the get method or null if the property is write-only. setMethodName the name of the set method or null if the property is read-only.

Throws: IntrospectionException if the methods are not found or invalid.

PropertyDescriptor

Create a new PropertyDescriptor using explicit Methods. Note that the methods will be checked for conformance to standard Property method rules, as described above at the top of this class.
It is possible to call this method with both Method arguments being null. In such a case the property type is null.

Parameters: name the programmatic name of the property, usually starting with a lowercase letter (e.g. fooManChu instead of FooManChu). readMethod the read method or null if the property is write-only. writeMethod the write method or null if the property is read-only.

Throws: IntrospectionException if the methods are not found or invalid.

Method Detail

createPropertyEditor

Instantiate a property editor using the property editor class. If no property editor class has been set, this will return null. If the editor class has a public constructor which takes a single argument, that will be used and the bean parameter will be passed to it. Otherwise, a public no-argument constructor will be used, if available. This method will return null if no constructor is found or if construction fails for any reason.

Parameters: bean the argument to the constructor

Returns: a new PropertyEditor, or null on error

Since: 1.5

equals

Compares this PropertyDescriptor against the given object. Two PropertyDescriptors are equals if

the read methods are equal
the write methods are equal
the property types are equals
the property editor classes are equal
the flags (constrained and bound) are equal

Returns: Whether both objects are equal according to the rules given above.

Since: 1.4

getPropertyEditorClass

Get the PropertyEditor class. Defaults to null. *

getPropertyType

Get the property type. This is the type the get method returns and the set method takes in.

getReadMethod

Get the get method. Why they call it readMethod here and get everywhere else is beyond me.

getWriteMethod

Get the set method. Why they call it writeMethod here and set everywhere else is beyond me.

hashCode

Return a hash code for this object, conforming to the contract described in {@link Object#hashCode()}.

Returns: the hash code

Since: 1.5

isBound

Get whether the property is bound. Defaults to false. *

isConstrained

Get whether the property is constrained. Defaults to false. *

setBound

Set whether the property is bound. As long as the the bean implements addPropertyChangeListener() and removePropertyChangeListener(), setBound(true) may safely be called.

If these things are not true, then the behavior of the system will be undefined.

When a property is bound, its set method is required to fire the PropertyChangeListener.propertyChange()) event after the value has changed.

Parameters: bound whether the property is bound or not.

setConstrained

Set whether the property is constrained. If the set method throws java.beans.PropertyVetoException (or subclass thereof) and the bean implements addVetoableChangeListener() and removeVetoableChangeListener(), then setConstrained(true) may safely be called. Otherwise, the system behavior is undefined. Spec note: given those strict parameters, it would be nice if it got set automatically by detection, but oh well.

When a property is constrained, its set method is required to:

Fire the VetoableChangeListener.vetoableChange() event notifying others of the change and allowing them a chance to say it is a bad thing.
If any of the listeners throws a PropertyVetoException, then it must fire another vetoableChange() event notifying the others of a reversion to the old value (though, of course, the change was never made). Then it rethrows the PropertyVetoException and exits.
If all has gone well to this point, the value may be changed.

Parameters: constrained whether the property is constrained or not.

setPropertyEditorClass

Set the PropertyEditor class. If the class does not implement the PropertyEditor interface, you will likely get an exception late in the game.

Parameters: propertyEditorClass the PropertyEditor class for this class to use.

setReadMethod

Sets the read method.
The read method is used to retrieve the value of a property. A legal read method must have no arguments. Its return type must not be void. If this methods succeeds the property type is adjusted to the return type of the read method.

It is legal to set the read and the write method to null or provide method which have been declared in distinct classes.

Parameters: readMethod The new method to be used or null.

Throws: IntrospectionException If the given method is invalid.

Since: 1.2

setWriteMethod

Sets the write method.
The write method is used to set the value of a property. A legal write method must have a single argument which can be assigned to the property. If no read method exists the property type changes to the argument type of the write method.

It is legal to set the read and the write method to null or provide method which have been declared in distinct classes.

Parameters: writeMethod The new method to be used or null.

Throws: IntrospectionException If the given method is invalid.

Since: 1.2

Class PropertyDescriptor