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The ANTLR 4 Runtime

There is a newer version: 4.13.2

/*
 * Copyright (c) 2012-2016 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.misc;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;

public class MultiMap extends LinkedHashMap> {
	public void map(K key, V value) {
		List elementsForKey = get(key);
		if ( elementsForKey==null ) {
			elementsForKey = new ArrayList();
			super.put(key, elementsForKey);
		}
		elementsForKey.add(value);
	}

	public List> getPairs() {
		List> pairs = new ArrayList>();
		for (K key : keySet()) {
			for (V value : get(key)) {
				pairs.add(new Pair(key, value));
			}
		}
		return pairs;
	}
}