ConstructUnary


1   // ============================================================================
2   // $Id: ConstructUnary.java,v 1.16 2006/05/08 02:23:26 davidahall Exp $
3   // Copyright (c) 2003-2005  David A. Hall
4   // ============================================================================
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19  // GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which
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32  
33  package net.sf.jga.fn.property;
34  
35  import java.lang.reflect.Constructor  ;
36  import java.lang.reflect.InvocationTargetException  ;
37  import java.text.MessageFormat  ;
38  import net.sf.jga.fn.EvaluationException;
39  import net.sf.jga.fn.UnaryFunctor;
40  
41  /**
42   * Unary Functor that constructs an object of the given class via a
43   * one-argument constructor.
44   * <p>
45   * Copyright &copy; 2003-2005  David A. Hall
46   *
47   * @author <a HREF="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
48   **/
49  
50  public class ConstructUnary<T,R> extends UnaryFunctor<T,R> {
51      
52      static final long serialVersionUID = -6046849006655934333L;
53  
54      // the type of the object built by the constructor
55      private Class  <R> _objclass;
56  
57      // the argument type for the constructor
58      private Class  <T> _argclass;
59  
60      // the constructor being invoked
61      private transient Constructor  <R> _ctor;
62  
63      /**
64       * Builds a functor that will build an object of class
65       * <code>ctorclass</code>, given an argument of class <code>argclass</code>.
66       * The classes passed to the constructor must be assignable to the generic
67       * arguments (when generics are in use):
68       * <code>
69       *    ConstructUnary<String,Integer> ctor =
70       *         new ConstructUnary<String,Integer>(String.class,Integer.class);
71       * </code>
72       * @throws IllegalArgumentException if either argument is omitted, or if the
73       * constructor cannot be found.
74       */
75      
76      public ConstructUnary(Class  <T> argclass, Class  <R> ctorclass) {
77          if (argclass == null) {
78              String   msg = "Argument Class must be specified";
79              throw new IllegalArgumentException  (msg);
80          }
81  
82          if (ctorclass == null) {
83              String   msg = "Class to be constructed must be specified";
84              throw new IllegalArgumentException  (msg);
85          }
86          
87          try {
88              _argclass = argclass;
89              _objclass = ctorclass;
90              _ctor = getConstructor();
91          }
92          catch (NoSuchMethodException   x) {
93              String   msg = "No constructor found for class {0} that takes an argument of class {1}";
94              Object   args[] = new Object  [] { ctorclass, argclass };
95              
96              IllegalArgumentException   x1 =
97                  new IllegalArgumentException  (MessageFormat.format(msg, args));
98              x1.initCause(x);
99              throw x1;
100         }
101     }
102 
103     
104     /**
105      * Lazily loads the constructor
106      */
107     public synchronized Constructor  <R> getConstructor() throws NoSuchMethodException   {
108         if (_ctor == null) 
109             _ctor = _objclass.getConstructor(new Class  []{_argclass});
110 
111         return _ctor;
112     }
113 
114     
115     // UnaryFunctor interface
116     
117     /**
118      * Builds an object via a one-arg constructor, passing the given value.
119      * <p>
120      * @return the object built by the constructor
121      */
122     public R fn(T arg) {
123         
124         try {
125             R val = (R) getConstructor().newInstance(new Object  []{arg});
126             return val;
127         }
128         catch (NoSuchMethodException   x) {
129             String   msg = "No constructor for class {0} that takes an argument of type {1}";
130             Object  [] args = new Object  []{_objclass.getName(), _argclass.getName()};
131             throw new EvaluationException(MessageFormat.format(msg,args), x);
132         }
133         catch (InstantiationException   x) {
134             String   msg = "class {0} is abstract: cannot be constructed";
135             Object  [] args = new Object  []{_objclass.getName()};
136             throw new EvaluationException(MessageFormat.format(msg,args), x);
137         }
138         catch (IllegalArgumentException   x) {
139             String   msg = "class {0} ctor({1}) cannot be called with {2}";
140             Object  [] args = new Object  []{_objclass.getName(), _argclass.getName(), arg};
141             throw new EvaluationException(MessageFormat.format(msg,args), x);
142         }
143         catch (IllegalAccessException   x) {
144             String   msg = "class {0} ctor({1}) is not accessible";
145             Object  [] args = new Object  []{_objclass.getName(), _argclass.getName()};
146             throw new EvaluationException(MessageFormat.format(msg,args), x);
147         }
148         catch (InvocationTargetException   x) { 
149             String   msg = "class {0} ctor({1}) failed: "+x.getMessage();
150             Object  [] args = new Object  []{_objclass.getName(), _argclass.getName()};
151             throw new EvaluationException(MessageFormat.format(msg,args), x);
152         }
153     }
154 
155     
156     /**
157      * Calls the Visitor's <code>visit(ConstructUnary)</code> method, if it
158      * implements the nested Visitor interface.
159      */
160     public void accept(net.sf.jga.fn.Visitor v) {
161         if (v instanceof ConstructUnary.Visitor)
162             ((ConstructUnary.Visitor)v).visit(this);
163         else
164             v.visit(this);
165     }
166 
167     // Object overrides
168 
169     public String   toString() {
170         return "new "+_objclass.getName()+"(["+_argclass.getName()+"])";
171     }
172     
173     // Acyclic Visitor
174     
175     /**
176      * Interface for classes that may interpret a <b>ConstructUnary</b>
177      * predicate.
178      */
179     public interface Visitor extends net.sf.jga.fn.Visitor {
180         public void visit(ConstructUnary host);
181     }
182 }
183
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