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Common module for front-facing implementations like REST.

There is a newer version: 3.0.4

/**
 * JBoss, Home of Professional Open Source.
 * Copyright 2014-2022 Red Hat, Inc., and individual contributors
 * as indicated by the @author tags.
 *
 * 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 org.jboss.pnc.facade.util;

import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Iterator that merges two sorted iterators.
 *
 * @author Honza Brázdil <[email protected]>
 */
public class MergeIterator implements Iterator {

    private final Iterator itA;
    private final Iterator itB;
    private final Comparator comparator;
    private T objectA;
    private T objectB;

    public MergeIterator(Iterator a, Iterator b, Comparator comparator) {
        this.itA = a;
        this.itB = b;
        this.comparator = comparator;
        if (itA.hasNext()) {
            objectA = itA.next();
        }
        if (itB.hasNext()) {
            objectB = itB.next();
        }
    }

    @Override
    public boolean hasNext() {
        return objectA != null || objectB != null || itA.hasNext() || itB.hasNext();
    }

    @Override
    public T next() {
        T object;
        if (objectA != null && objectB != null) {
            if (comparator.compare(objectA, objectB) < 0) {
                object = objectA;
                objectA = provideNext(itA);
            } else {
                object = objectB;
                objectB = provideNext(itB);
            }
        } else if (objectA != null) {
            object = objectA;
            objectA = provideNext(itA);
        } else if (objectB != null) {
            object = objectB;
            objectB = provideNext(itB);
        } else {
            throw new NoSuchElementException();
        }
        return object;
    }

    private T provideNext(Iterator it) {
        if (it.hasNext()) {
            return it.next();
        } else {
            return null;
        }
    }

}