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Java > Open Source Codes > sample > vector > VectorAssistant


1 package sample.vector;
2
3 import java.io.IOException JavaDoc;
4 import javassist.*;
5 import javassist.preproc.Assistant;
6
7 /**
8  * This is a Javassist program which produce a new class representing
9  * vectors of a given type. For example,
10  *
11  * <ul>import java.util.Vector by sample.vector.VectorAssistant(int)</ul>
12  *
13  * <p>requests the Javassist preprocessor to substitute the following
14  * lines for the original import declaration:
15  *
16  * <ul><pre>
17  * import java.util.Vector;
18  * import sample.vector.intVector;
19  * </pre></ul>
20  *
21  * <p>The Javassist preprocessor calls <code>VectorAssistant.assist()</code>
22  * and produces class <code>intVector</code> equivalent to:
23  *
24  * <ul><pre>
25  * package sample.vector;
26  *
27  * public class intVector extends Vector {
28  * pubilc void add(int value) {
29  * addElement(new Integer(value));
30  * }
31  *
32  * public int at(int index) {
33  * return elementAt(index).intValue();
34  * }
35  * }
36  * </pre></ul>
37  *
38  * <p><code>VectorAssistant.assist()</code> uses
39  * <code>sample.vector.Sample</code> and <code>sample.vector.Sample2</code>
40  * as a template to produce the methods <code>add()</code> and
41  * <code>at()</code>.
42  */
43 public class VectorAssistant implements Assistant {
44     public final String JavaDoc packageName = "sample.vector.";
45
46     /**
47      * Calls <code>makeSubclass()</code> and produces a new vector class.
48      * This method is called by a <code>javassist.preproc.Compiler</code>.
49      *
50      * @see javassist.preproc.Compiler
51      */
52     public CtClass[] assist(ClassPool pool, String JavaDoc vec, String JavaDoc[] args)
53     throws CannotCompileException
54     {
55     if (args.length != 1)
56         throw new CannotCompileException(
57             "VectorAssistant receives a single argument.");
58
59     try {
60         CtClass subclass;
61         CtClass elementType = pool.get(args[0]);
62         if (elementType.isPrimitive())
63         subclass = makeSubclass2(pool, elementType);
64         else
65         subclass = makeSubclass(pool, elementType);
66
67         CtClass[] results = { subclass, pool.get(vec) };
68         return results;
69     }
70     catch (NotFoundException e) {
71         throw new CannotCompileException(e);
72     }
73     catch (IOException JavaDoc e) {
74         throw new CannotCompileException(e);
75     }
76     }
77
78     /**
79      * Produces a new vector class. This method does not work if
80      * the element type is a primitive type.
81      *
82      * @param type the type of elements
83      */
84     public CtClass makeSubclass(ClassPool pool, CtClass type)
85     throws CannotCompileException, NotFoundException, IOException JavaDoc
86     {
87     CtClass vec = pool.makeClass(makeClassName(type));
88     vec.setSuperclass(pool.get("java.util.Vector"));
89
90     CtClass c = pool.get("sample.vector.Sample");
91     CtMethod addmethod = c.getDeclaredMethod("add");
92     CtMethod atmethod = c.getDeclaredMethod("at");
93
94     ClassMap map = new ClassMap();
95     map.put("sample.vector.X", type.getName());
96
97     vec.addMethod(CtNewMethod.copy(addmethod, "add", vec, map));
98     vec.addMethod(CtNewMethod.copy(atmethod, "at", vec, map));
99     vec.writeFile();
100     return vec;
101     }
102
103     /**
104      * Produces a new vector class. This uses wrapped methods so that
105      * the element type can be a primitive type.
106      *
107      * @param type the type of elements
108      */
109     public CtClass makeSubclass2(ClassPool pool, CtClass type)
110     throws CannotCompileException, NotFoundException, IOException JavaDoc
111     {
112     CtClass vec = pool.makeClass(makeClassName(type));
113     vec.setSuperclass(pool.get("java.util.Vector"));
114
115     CtClass c = pool.get("sample.vector.Sample2");
116     CtMethod addmethod = c.getDeclaredMethod("add");
117     CtMethod atmethod = c.getDeclaredMethod("at");
118
119     CtClass[] args1 = { type };
120     CtClass[] args2 = { CtClass.intType };
121     CtMethod m
122         = CtNewMethod.wrapped(CtClass.voidType, "add", args1,
123                   null, addmethod, null, vec);
124     vec.addMethod(m);
125     m = CtNewMethod.wrapped(type, "at", args2,
126                 null, atmethod, null, vec);
127     vec.addMethod(m);
128     vec.writeFile();
129     return vec;
130     }
131
132     private String JavaDoc makeClassName(CtClass type) {
133     return packageName + type.getSimpleName() + "Vector";
134     }
135 }
136
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