View Javadoc

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  /*** 
20   * Super class for JSR - Jump to subroutine
21   *
22   * @version $Id: JsrInstruction.java 386056 2006-03-15 11:31:56Z tcurdt $
23   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
24   */
25  public abstract class JsrInstruction extends BranchInstruction implements UnconditionalBranch,
26          TypedInstruction, StackProducer {
27  
28      JsrInstruction(short opcode, InstructionHandle target) {
29          super(opcode, target);
30      }
31  
32  
33      /***
34       * Empty constructor needed for the Class.newInstance() statement in
35       * Instruction.readInstruction(). Not to be used otherwise.
36       */
37      JsrInstruction() {
38      }
39  
40  
41      /*** @return return address type
42       */
43      public Type getType( ConstantPoolGen cp ) {
44          return new ReturnaddressType(physicalSuccessor());
45      }
46  
47  
48      /***
49       * Returns an InstructionHandle to the physical successor
50       * of this JsrInstruction. <B>For this method to work,
51       * this JsrInstruction object must not be shared between
52       * multiple InstructionHandle objects!</B>
53       * Formally, there must not be InstructionHandle objects
54       * i, j where i != j and i.getInstruction() == this ==
55       * j.getInstruction().
56       * @return an InstructionHandle to the "next" instruction that
57       * will be executed when RETurned from a subroutine.
58       */
59      public InstructionHandle physicalSuccessor() {
60          InstructionHandle ih = this.target;
61          // Rewind!
62          while (ih.getPrev() != null) {
63              ih = ih.getPrev();
64          }
65          // Find the handle for "this" JsrInstruction object.
66          while (ih.getInstruction() != this) {
67              ih = ih.getNext();
68          }
69          InstructionHandle toThis = ih;
70          while (ih != null) {
71              ih = ih.getNext();
72              if ((ih != null) && (ih.getInstruction() == this)) {
73                  throw new RuntimeException("physicalSuccessor() called on a shared JsrInstruction.");
74              }
75          }
76          // Return the physical successor		
77          return toThis.getNext();
78      }
79  }