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/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

package org.antlr.v4.runtime.tree;

public abstract class AbstractParseTreeVisitor implements ParseTreeVisitor {
	/**
	 * {@inheritDoc}
	 *
	 * 

The default implementation calls {@link ParseTree#accept} on the * specified tree.

*/ @Override public T visit(ParseTree tree) { return tree.accept(this); } /** * {@inheritDoc} * *

The default implementation initializes the aggregate result to * {@link #defaultResult defaultResult()}. Before visiting each child, it * calls {@link #shouldVisitNextChild shouldVisitNextChild}; if the result * is {@code false} no more children are visited and the current aggregate * result is returned. After visiting a child, the aggregate result is * updated by calling {@link #aggregateResult aggregateResult} with the * previous aggregate result and the result of visiting the child.

* *

The default implementation is not safe for use in visitors that modify * the tree structure. Visitors that modify the tree should override this * method to behave properly in respect to the specific algorithm in use.

*/ @Override public T visitChildren(RuleNode node) { T result = defaultResult(); int n = node.getChildCount(); for (int i=0; iThe default implementation returns the result of * {@link #defaultResult defaultResult}.

*/ @Override public T visitTerminal(TerminalNode node) { return defaultResult(); } /** * {@inheritDoc} * *

The default implementation returns the result of * {@link #defaultResult defaultResult}.

*/ @Override public T visitErrorNode(ErrorNode node) { return defaultResult(); } /** * Gets the default value returned by visitor methods. This value is * returned by the default implementations of * {@link #visitTerminal visitTerminal}, {@link #visitErrorNode visitErrorNode}. * The default implementation of {@link #visitChildren visitChildren} * initializes its aggregate result to this value. * *

The base implementation returns {@code null}.

* * @return The default value returned by visitor methods. */ protected T defaultResult() { return null; } /** * Aggregates the results of visiting multiple children of a node. After * either all children are visited or {@link #shouldVisitNextChild} returns * {@code false}, the aggregate value is returned as the result of * {@link #visitChildren}. * *

The default implementation returns {@code nextResult}, meaning * {@link #visitChildren} will return the result of the last child visited * (or return the initial value if the node has no children).

* * @param aggregate The previous aggregate value. In the default * implementation, the aggregate value is initialized to * {@link #defaultResult}, which is passed as the {@code aggregate} argument * to this method after the first child node is visited. * @param nextResult The result of the immediately preceeding call to visit * a child node. * * @return The updated aggregate result. */ protected T aggregateResult(T aggregate, T nextResult) { return nextResult; } /** * This method is called after visiting each child in * {@link #visitChildren}. This method is first called before the first * child is visited; at that point {@code currentResult} will be the initial * value (in the default implementation, the initial value is returned by a * call to {@link #defaultResult}. This method is not called after the last * child is visited. * *

The default implementation always returns {@code true}, indicating that * {@code visitChildren} should only return after all children are visited. * One reason to override this method is to provide a "short circuit" * evaluation option for situations where the result of visiting a single * child has the potential to determine the result of the visit operation as * a whole.

* * @param node The {@link RuleNode} whose children are currently being * visited. * @param currentResult The current aggregate result of the children visited * to the current point. * * @return {@code true} to continue visiting children. Otherwise return * {@code false} to stop visiting children and immediately return the * current aggregate result from {@link #visitChildren}. */ protected boolean shouldVisitNextChild(RuleNode node, T currentResult) { return true; } }




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