javacc-doc 5.0-4 / usr / share / doc / javacc / examples / JJTreeExamples / Eg4DumpVisitor.java

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/**
 *  This is an example of how the Visitor pattern might be used to
 *  implement the dumping code that comes with SimpleNode.  It's a bit
 *  long-winded, but it does illustrate a couple of the main points.
 *  <ol>
 *  <li> the visitor can maintain state between the nodes that it visits
 *  (for example the current indentation level).
 *  </li>
 *
 *  <li>if you don't implement a jjtAccept() method for a subclass of
 *  SimpleNode, then SimpleNode's acceptor will get called.
 *  </li>
 *  <li> the utility method childrenAccept() can be useful when
 *  implementing preorder or postorder tree walks.
 *  </li>
 *  </ol>
 *
 */

public class Eg4DumpVisitor implements Eg4Visitor
{
  private int indent = 0;

  private String indentString() {
    StringBuffer sb = new StringBuffer();
    for (int i = 0; i < indent; ++i) {
      sb.append(' ');
    }
    return sb.toString();
  }

  public Object visit(SimpleNode node, Object data) {
    System.out.println(indentString() + node +
                   ": acceptor not unimplemented in subclass?");
    ++indent;
    data = node.childrenAccept(this, data);
    --indent;
    return data;
  }

  public Object visit(ASTStart node, Object data) {
    System.out.println(indentString() + node);
    ++indent;
    data = node.childrenAccept(this, data);
    --indent;
    return data;
  }

  public Object visit(ASTAdd node, Object data) {
    System.out.println(indentString() + node);
    ++indent;
    data = node.childrenAccept(this, data);
    --indent;
    return data;
  }

  public Object visit(ASTMult node, Object data) {
    System.out.println(indentString() + node);
    ++indent;
    data = node.childrenAccept(this, data);
    --indent;
    return data;
  }

  public Object visit(ASTMyOtherID node, Object data) {
    System.out.println(indentString() + node);
    ++indent;
    data = node.childrenAccept(this, data);
    --indent;
    return data;
  }

  public Object visit(ASTInteger node, Object data) {
    System.out.println(indentString() + node);
    ++indent;
    data = node.childrenAccept(this, data);
    --indent;
    return data;
  }
}

/*end*/