ParserDumpVisitor


1   /**
2    *
3    * Copyright (c) 1996-1997 Sun Microsystems, Inc.
4    *
5    * Use of this file and the system it is part of is constrained by the
6    * file COPYRIGHT in the root directory of this system.
7    *
8    */
9   
10  /* This is an example of how the Visitor pattern might be used to
11     implement the dumping code that comes with SimpleNode.  It's a bit
12     long-winded, but it does illustrate a couple of the main points.
13  
14     1) the visitor can maintain state between the nodes that it visits
15     (for example the current indentation level).
16  
17     2) if you don't implement a jjtAccept() method for a subclass of
18     SimpleNode, then SimpleNode's acceptor will get called.
19  
20     3) the utility method childrenAccept() can be useful when
21     implementing preorder or postorder tree walks.
22  
23     Err, that's it. */
24     
25  package org.nfunk.jep;
26  
27  public class ParserDumpVisitor implements ParserVisitor
28  {
29    private int indent = 0;
30  
31    private String   indentString() {
32      StringBuffer   sb = new StringBuffer  ();
33      for (int i = 0; i < indent; ++i) {
34        sb.append("  ");
35      }
36      return sb.toString();
37    }
38  
39    public Object   visit(SimpleNode node, Object   data) throws ParseException {
40      System.out.println(indentString() + node +
41                 ": acceptor not unimplemented in subclass?");
42      ++indent;
43      data = node.childrenAccept(this, data);
44      --indent;
45      return data;
46    }
47  
48    public Object   visit(ASTStart node, Object   data) throws ParseException {
49      System.out.println(indentString() + node);
50      ++indent;
51      data = node.childrenAccept(this, data);
52      --indent;
53      return data;
54    }
55  
56    public Object   visit(ASTFunNode node, Object   data) throws ParseException {
57      System.out.println(indentString() + node);
58      ++indent;
59      data = node.childrenAccept(this, data);
60      --indent;
61      return data;
62    }
63  
64    public Object   visit(ASTVarNode node, Object   data) throws ParseException {
65      System.out.println(indentString() + node);
66      ++indent;
67      data = node.childrenAccept(this, data);
68      --indent;
69      return data;
70    }
71  
72    public Object   visit(ASTConstant node, Object   data) throws ParseException {
73      System.out.println(indentString() + node);
74      ++indent;
75      data = node.childrenAccept(this, data);
76      --indent;
77      return data;
78    }
79  }
80  
81  /*end*/
82
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