| package org.eclipse.persistence.internal.libraries.antlr.runtime.tree; |
| |
| /** Do a depth first walk of a tree, applying pre() and post() actions |
| * as we discover and finish nodes. |
| */ |
| public class TreeVisitor { |
| protected TreeAdaptor adaptor; |
| |
| public TreeVisitor(TreeAdaptor adaptor) { |
| this.adaptor = adaptor; |
| } |
| public TreeVisitor() { this(new CommonTreeAdaptor()); } |
| |
| /** Visit every node in tree t and trigger an action for each node |
| * before/after having visited all of its children. |
| * Execute both actions even if t has no children. |
| * If a child visit yields a new child, it can update its |
| * parent's child list or just return the new child. The |
| * child update code works even if the child visit alters its parent |
| * and returns the new tree. |
| * |
| * Return result of applying post action to this node. |
| */ |
| public Object visit(Object t, TreeVisitorAction action) { |
| // System.out.println("visit "+((Tree)t).toStringTree()); |
| boolean isNil = adaptor.isNil(t); |
| if ( action!=null && !isNil ) { |
| t = action.pre(t); // if rewritten, walk children of new t |
| } |
| int n = adaptor.getChildCount(t); |
| for (int i=0; i<n; i++) { |
| Object child = adaptor.getChild(t, i); |
| Object visitResult = visit(child, action); |
| Object childAfterVisit = adaptor.getChild(t, i); |
| if ( visitResult != childAfterVisit ) { // result & child differ? |
| adaptor.setChild(t, i, visitResult); |
| } |
| } |
| if ( action!=null && !isNil ) t = action.post(t); |
| return t; |
| } |
| } |