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Java > Open Source Codes > org > apache > bcel > generic > LocalVariableInstruction


1 /*
2  * Copyright 2000-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  *
16  */
17 package org.apache.bcel.generic;
18
19 import java.io.DataOutputStream JavaDoc;
20 import java.io.IOException JavaDoc;
21 import org.apache.bcel.Constants;
22 import org.apache.bcel.util.ByteSequence;
23
24 /**
25  * Abstract super class for instructions dealing with local variables.
26  *
27  * @version $Id: LocalVariableInstruction.java 386056 2006-03-15 11:31:56Z tcurdt $
28  * @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
29  */
30 public abstract class LocalVariableInstruction extends Instruction implements TypedInstruction,
31         IndexedInstruction {
32
33     protected int n = -1; // index of referenced variable
34 private short c_tag = -1; // compact version, such as ILOAD_0
35 private short canon_tag = -1; // canonical tag such as ILOAD
36
37
38     private final boolean wide() {
39         return n > Constants.MAX_BYTE;
40     }
41
42
43     /**
44      * Empty constructor needed for the Class.newInstance() statement in
45      * Instruction.readInstruction(). Not to be used otherwise.
46      * tag and length are defined in readInstruction and initFromFile, respectively.
47      */
48     LocalVariableInstruction(short canon_tag, short c_tag) {
49         super();
50         this.canon_tag = canon_tag;
51         this.c_tag = c_tag;
52     }
53
54
55     /**
56      * Empty constructor needed for the Class.newInstance() statement in
57      * Instruction.readInstruction(). Also used by IINC()!
58      */
59     LocalVariableInstruction() {
60     }
61
62
63     /**
64      * @param opcode Instruction opcode
65      * @param c_tag Instruction number for compact version, ALOAD_0, e.g.
66      * @param n local variable index (unsigned short)
67      */
68     protected LocalVariableInstruction(short opcode, short c_tag, int n) {
69         super(opcode, (short) 2);
70         this.c_tag = c_tag;
71         canon_tag = opcode;
72         setIndex(n);
73     }
74
75
76     /**
77      * Dump instruction as byte code to stream out.
78      * @param out Output stream
79      */
80     public void dump( DataOutputStream JavaDoc out ) throws IOException JavaDoc {
81         if (wide()) {
82             out.writeByte(Constants.WIDE);
83         }
84         out.writeByte(opcode);
85         if (length > 1) { // Otherwise ILOAD_n, instruction, e.g.
86 if (wide()) {
87                 out.writeShort(n);
88             } else {
89                 out.writeByte(n);
90             }
91         }
92     }
93
94
95     /**
96      * Long output format:
97      *
98      * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]"
99      * "("&lt;length of instruction&gt;")" "&lt;"&lt; local variable index&gt;"&gt;"
100      *
101      * @param verbose long/short format switch
102      * @return mnemonic for instruction
103      */
104     public String JavaDoc toString( boolean verbose ) {
105         if (((opcode >= Constants.ILOAD_0) && (opcode <= Constants.ALOAD_3))
106                 || ((opcode >= Constants.ISTORE_0) && (opcode <= Constants.ASTORE_3))) {
107             return super.toString(verbose);
108         } else {
109             return super.toString(verbose) + " " + n;
110         }
111     }
112
113
114     /**
115      * Read needed data (e.g. index) from file.
116      * PRE: (ILOAD <= tag <= ALOAD_3) || (ISTORE <= tag <= ASTORE_3)
117      */
118     protected void initFromFile( ByteSequence bytes, boolean wide ) throws IOException JavaDoc {
119         if (wide) {
120             n = bytes.readUnsignedShort();
121             length = 4;
122         } else if (((opcode >= Constants.ILOAD) && (opcode <= Constants.ALOAD))
123                 || ((opcode >= Constants.ISTORE) && (opcode <= Constants.ASTORE))) {
124             n = bytes.readUnsignedByte();
125             length = 2;
126         } else if (opcode <= Constants.ALOAD_3) { // compact load instruction such as ILOAD_2
127 n = (opcode - Constants.ILOAD_0) % 4;
128             length = 1;
129         } else { // Assert ISTORE_0 <= tag <= ASTORE_3
130 n = (opcode - Constants.ISTORE_0) % 4;
131             length = 1;
132         }
133     }
134
135
136     /**
137      * @return local variable index referred by this instruction.
138      */
139     public final int getIndex() {
140         return n;
141     }
142
143
144     /**
145      * Set the local variable index
146      */
147     public void setIndex( int n ) {
148         if ((n < 0) || (n > Constants.MAX_SHORT)) {
149             throw new ClassGenException("Illegal value: " + n);
150         }
151         this.n = n;
152         if (n >= 0 && n <= 3) { // Use more compact instruction xLOAD_n
153 opcode = (short) (c_tag + n);
154             length = 1;
155         } else {
156             opcode = canon_tag;
157             if (wide()) {
158                 length = 4;
159             } else {
160                 length = 2;
161             }
162         }
163     }
164
165
166     /** @return canonical tag for instruction, e.g., ALOAD for ALOAD_0
167      */
168     public short getCanonicalTag() {
169         return canon_tag;
170     }
171
172
173     /**
174      * Returns the type associated with the instruction -
175      * in case of ALOAD or ASTORE Type.OBJECT is returned.
176      * This is just a bit incorrect, because ALOAD and ASTORE
177      * may work on every ReferenceType (including Type.NULL) and
178      * ASTORE may even work on a ReturnaddressType .
179      * @return type associated with the instruction
180      */
181     public Type getType( ConstantPoolGen cp ) {
182         switch (canon_tag) {
183             case Constants.ILOAD:
184             case Constants.ISTORE:
185                 return Type.INT;
186             case Constants.LLOAD:
187             case Constants.LSTORE:
188                 return Type.LONG;
189             case Constants.DLOAD:
190             case Constants.DSTORE:
191                 return Type.DOUBLE;
192             case Constants.FLOAD:
193             case Constants.FSTORE:
194                 return Type.FLOAT;
195             case Constants.ALOAD:
196             case Constants.ASTORE:
197                 return Type.OBJECT;
198             default:
199                 throw new ClassGenException("Oops: unknown case in switch" + canon_tag);
200         }
201     }
202 }
203
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