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org.jdaemon.util.data
Class Type  

java.lang.Object
  org.jdaemon.util.data.Type

Direct Known Subclasses:

AbstractType, ArrayType, QuickListType

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public abstract class Type

extends java.lang.Object

Mechanism for persisting Java objects in a DataRepresentation.

The Type object allows Java objects to be both retrieved from and written to a DataRepresentation.

A single Type object provides a mapping between the element type stored in a DataRepresentation and the class of a java object. For instance a java object of class 'org.jdaemon.Polygon' might have an element type of 'POLYGON'.

In addition, Type has two abstract methods (read and write) which must be implemented in order to define the exact mapping between fields of a java class and attributes of an element representing that class in a DataRepresentation.

Trivially, then, if POLYGON is an instance of an appropriate type object, and polygon is an instance of the Polygon class, polygon could be written to a data representation using:

POLYGON.put(data_representation, "example", polygon)

and read from a data representation using:

polygon = (Polygon)POLYGON.get(data_representation, "example")

Type also provides for polymorphism, allowing an object to be retrieved from a DataRepresentation without knowing its exact class. A tree of Type objects is created that specifies a notional inheritance tree (or type hierarchy) for the elements stored in a DataRepresentation. This will generally be similar to the type hierarchy of the java objects to be stored in the DataRepresentation.

The tree of Type objects is created using the addSubtype method. For example, given three classes, Drawable, Polygon, and Rectangle, where Polygon and Rectangle are both subclasses of Drawable, it would be natural to create three Type objects, POLYGON, RECTANGLE, and DRAWABLE.

If POLYGON and RECTANGLE are both added as subtypes of DRAWABLE, then it will be possible to read and write both polygon and rectangle objects using the DRAWABLE type. So:

drawable = (Drawable)DRAWABLE.get(data_representation, "example")

would correctly instantiate either a Polygon or a Rectangle object depending on the element type stored in the data representation.

Version:

0.1

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Field Summary
private  java.lang.Class	my_class           The java class represented by this type
private  java.util.LinkedList	subtypes           A list of subtypes of this type
private  java.lang.String	type           The name of this type.

 

Constructor Summary

Type(java.lang.String type, java.lang.Class my_class)           Construct a Type object to map between objects of a given class and DataRepresentation elements of a given type.

Type(Type parent, java.lang.String type, java.lang.Class my_class)           Construct a Type object to map between objects of a given class and DataRepresentation elements of a given type.

 

Method Summary
protected  void	addSubtype(Type type)           Add a subtype to this type.
java.lang.Object	get(DataRepresentation representation)
java.lang.Object	get(DataRepresentation representation, java.lang.Object key)           Reads an object from the specified element of a DataRepresentation
java.lang.Class	getJavaClass()
java.lang.String	getName()           Get the element type for which this Type provides a mapping.
Type	getType(DataRepresentation representation)           Find the actual type of some DataRepresentation.
Type	getType(java.lang.Object object)           Find the actual type of some object.
void	put(DataRepresentation representation, java.lang.Object key, java.lang.Object object)           Writes an object as an element of a DataRepresentation
abstract  java.lang.Object	read(DataRepresentation representation)           Reads an object of this exact type from some DataRepresentation.
abstract  void	write(DataRepresentation representation, java.lang.Object object)           Writes an object of this exact type to some DataRepresentation.

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Field Detail

type

private java.lang.String type

The name of this type. Maps to the element type in a datarepresentation

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my_class

private java.lang.Class my_class

The java class represented by this type

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subtypes

private java.util.LinkedList subtypes

A list of subtypes of this type

Constructor Detail

Type

public Type(java.lang.String type,
            java.lang.Class my_class)

Construct a Type object to map between objects of a given class and DataRepresentation elements of a given type.

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Type

public Type(Type parent,
            java.lang.String type,
            java.lang.Class my_class)

Construct a Type object to map between objects of a given class and DataRepresentation elements of a given type. This constructor is equivalent to building an object with Type(type, my_class) and then adding that object as a subtype of some parent Type with parent's addSubtype method.

Method Detail

getName

public java.lang.String getName()

Get the element type for which this Type provides a mapping.

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getJavaClass

public java.lang.Class getJavaClass()

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addSubtype

protected void addSubtype(Type type)

Add a subtype to this type.

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read

public abstract java.lang.Object read(DataRepresentation representation)
                               throws ReadError,
                                      ObjectInstantiationError

Reads an object of this exact type from some DataRepresentation. Implement this method in order to define the mapping from attributes/sub-elements of a data representation to the fields of an object.

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write

public abstract void write(DataRepresentation representation,
                           java.lang.Object object)
                    throws WriteError

Writes an object of this exact type to some DataRepresentation. Implement this method in order to define the mapping from the fields of an object to attributes/sub-elements of a data representation

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getType

public Type getType(DataRepresentation representation)
             throws ReadError

Find the actual type of some DataRepresentation.

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getType

public Type getType(java.lang.Object object)

Find the actual type of some object.

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get

public java.lang.Object get(DataRepresentation representation)
                     throws ReadError,
                            ObjectInstantiationError

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get

public java.lang.Object get(DataRepresentation representation,
                            java.lang.Object key)
                     throws ReadError,
                            ObjectInstantiationError

Reads an object from the specified element of a DataRepresentation

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put

public void put(DataRepresentation representation,
                java.lang.Object key,
                java.lang.Object object)
         throws WriteError

Writes an object as an element of a DataRepresentation

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> org >> jdaemon >> util >> [ data overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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