org.novelang.common.tree.ImmutableTree.java Source code

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Here is the source code for org.novelang.common.tree.ImmutableTree.java

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/*
 * Copyright (C) 2011 Laurent Caillette
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation, either
 * version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.novelang.common.tree;

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import com.google.common.collect.Lists;
import com.google.common.collect.ObjectArrays;
import org.apache.commons.lang.NullArgumentException;

/**
 * Immutable base class for homogeneous n-ary trees.
 * <p>
 * This class is generic for strong-typing the {@link Tree#adopt(Iterable)}} method.
 * 
 * @author Laurent Caillette
 */
public abstract class ImmutableTree<T extends Tree<T>> implements Tree<T> {

    /**
     * Don't be stupid using reflection to make this mutable!
     */
    private final T[] children;

    /**
     * Constructor.
     * @param children may be null but may not contain nulls.
     * @throws NullArgumentException
     */
    protected ImmutableTree(final T... children) throws NullArgumentException {
        this(Lists.newArrayList(children));
    }

    /**
     * Constructor.
     * @param children a non-null iterable returning non-null iterators iterating over
     *     non-null objects.
     * @throws NullArgumentException
     */
    protected ImmutableTree(final Iterable<? extends T> children) throws NullArgumentException {
        final List<T> childList = Lists.newArrayList(children);
        if (childList.isEmpty()) {
            this.children = null;
        } else {
            this.children = (T[]) createArray(this, childList.get(0), childList.size());
            for (int i = 0; i < childList.size(); i++) {
                final T child = childList.get(i);
                if (null == child) {
                    throw new NullArgumentException("Null child at index " + i);
                }
                this.children[i] = childList.get(i);
            }
        }
    }

    @Override
    public final int getChildCount() {
        return null == children ? 0 : children.length;
    }

    @Override
    public final T getChildAt(final int index) {
        if (index >= getChildCount()) {
            throw new ArrayIndexOutOfBoundsException(
                    "Unsupported index: " + index + " (child count: " + getChildCount() + ")");
        }
        return children[index];
    }

    /**
     * Convenience method (not a part of {@link Tree} contract).
     *
     * @return a non-null iterable returning non-null iterators, which iterate on non-null objects.
     */
    public Iterable<? extends T> getChildren() {
        return new Iterable() {
            @Override
            public Iterator<T> iterator() {
                return new ChildrenIterator();
            }
        };
    }

    private class ChildrenIterator implements Iterator<T> {

        private int current = 0;

        @Override
        public boolean hasNext() {
            return current < getChildCount();
        }

        @Override
        public T next() throws NoSuchElementException {
            if (hasNext()) {
                return ImmutableTree.this.getChildAt(current++);
            } else {
                throw new NoSuchElementException("No more children (child count: " + getChildCount() + ")");
            }
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException("remove");
        }
    }

    /**
     * Creates an array for storing children.
     * If the concrete instance ({@code this}) is an instance of 
     * {@link org.novelang.common.tree.StorageTypeProvider}, then returned array is of type
     * returned by {@link StorageTypeProvider#getStorageType()}.
     * Otherwise, it is of the type of the {@code fallback} parameter.
     * <p>
     * This method is used internally.
     * It is made a member of {@code ImmutableTree} in order to avoid a cyclic depedency
     * with {@code TreeTools} (which would be the logical place).
     *
     * @param fallback a non-null object.
     * @param arraySize a non-negative number.
     * @return a non-null array of the given size.
     *
     * @see org.novelang.common.tree.StorageTypeProvider
     */
    protected static <T extends Tree> T[] createArray(final T tree, final T fallback, final int arraySize) {
        final Class<T> concreteClass;
        if (tree instanceof StorageTypeProvider) {
            concreteClass = ((StorageTypeProvider) tree).getStorageType();
        } else {
            concreteClass = (Class<T>) fallback.getClass();
        }
        return ObjectArrays.newArray(concreteClass, arraySize);
    }

}