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// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.lib.actions;
import java.util.HashMap;
import java.util.Map;
/**
* A visitor helper class for bipartite graphs. The alternate kinds of nodes
* are arbitrarily designated "black" or "white".
*
* <p> Subclasses implement the black() and white() hook functions which are
* called as nodes are visited. The class holds a mapping from each node to a
* small integer; this is available to subclasses if they wish.
*/
public abstract class BipartiteVisitor<BLACK, WHITE> {
protected BipartiteVisitor() {}
private int nextNodeId = 0;
// Maps each visited black node to a small integer.
protected final Map<BLACK, Integer> visitedBlackNodes = new HashMap<>();
// Maps each visited white node to a small integer.
protected final Map<WHITE, Integer> visitedWhiteNodes = new HashMap<>();
/**
* Visit the specified black node. If this node has not already been
* visited, the black() hook is called and true is returned; otherwise,
* false is returned.
*/
public final boolean visitBlackNode(BLACK blackNode) {
if (blackNode == null) { throw new NullPointerException(); }
if (!visitedBlackNodes.containsKey(blackNode)) {
visitedBlackNodes.put(blackNode, nextNodeId++);
black(blackNode);
return true;
}
return false;
}
/**
* Visit all specified black nodes.
*/
public final void visitBlackNodes(Iterable<BLACK> blackNodes) {
for (BLACK blackNode : blackNodes) {
visitBlackNode(blackNode);
}
}
/**
* Visit the specified white node. If this node has not already been
* visited, the white() hook is called and true is returned; otherwise,
* false is returned.
*/
public final boolean visitWhiteNode(WHITE whiteNode) {
if (whiteNode == null) {
throw new NullPointerException();
}
if (!visitedWhiteNodes.containsKey(whiteNode)) {
visitedWhiteNodes.put(whiteNode, nextNodeId++);
white(whiteNode);
return true;
}
return false;
}
/**
* Visit all specified white nodes.
*/
public final void visitWhiteNodes(Iterable<WHITE> whiteNodes) {
for (WHITE whiteNode : whiteNodes) {
visitWhiteNode(whiteNode);
}
}
/**
* Called whenever a white node is visited. Hook for subclasses.
*/
protected abstract void white(WHITE whiteNode);
/**
* Called whenever a black node is visited. Hook for subclasses.
*/
protected abstract void black(BLACK blackNode);
}
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