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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.prelude.query;
import com.yahoo.api.annotations.Beta;
/**
* Query tree helper methods and factories.
*
* @author Steinar Knutsen
*/
@Beta
public final class ToolBox {
public static abstract class QueryVisitor {
/**
* Called for each item in the query tree given to
* {@link ToolBox#visit(QueryVisitor, Item)}. Return true to visit the
* sub-items of the given item, return false to ignore the sub-items.
*
* @param item each item in the query tree
* @return whether or not to visit the sub-items of the argument item
* (and then invoke the {@link #onExit()} method)
*/
public abstract boolean visit(Item item);
/**
* Invoked when all sub-items have been visited, or immediately after
* visit() if there are no sub-items or visit() returned false.
* This default implementation does nothing.
*/
public void onExit() {}
}
public static void visit(QueryVisitor visitor, Item item) {
if (item instanceof CompositeItem) {
if (visitor.visit(item)) {
CompositeItem composite = (CompositeItem) item;
for (int i = 0; i < composite.getItemCount(); ++i) {
visit(visitor, composite.getItem(i));
}
}
} else {
visitor.visit(item);
}
visitor.onExit();
}
}
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