net.derquinse.common.collect.EmptyImmutableHierarchy.java Source code

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Here is the source code for net.derquinse.common.collect.EmptyImmutableHierarchy.java

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/*
 * Copyright 2008-2010 the original author or authors.
 *
 * 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 net.derquinse.common.collect;

import java.util.List;

import javax.annotation.Nullable;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;

/**
 * An empty immutable hierarchy.
 * @author Andres Rodriguez
 */
final class EmptyImmutableHierarchy extends ImmutableHierarchy<Object> {
    static final EmptyImmutableHierarchy INSTANCE = new EmptyImmutableHierarchy();

    private EmptyImmutableHierarchy() {
    }

    @Override
    public ImmutableSet<Object> elementSet() {
        return ImmutableSet.of();
    }

    /*
     * (non-Javadoc)
     * @see net.derquinse.common.collect.Hierarchy#getChildren(java.lang.Object)
     */
    public List<Object> getChildren(@Nullable Object element) {
        if (element == null) {
            return getFirstLevel();
        }
        checkMember(element);
        return ImmutableList.of();
    }

    /*
     * (non-Javadoc)
     * @see net.derquinse.common.collect.Hierarchy#getFirstLevel()
     */
    public List<Object> getFirstLevel() {
        return ImmutableList.of();
    }

    /*
     * (non-Javadoc)
     * @see net.derquinse.common.collect.Hierarchy#getParent(java.lang.Object)
     */
    public Object getParent(Object element) {
        checkMember(element);
        return null;
    }

    /*
     * (non-Javadoc)
     * @see net.derquinse.common.collect.Hierarchy#getRoot()
     */
    public Object getRoot() {
        throw new IllegalStateException("An empty hierarchy has no root");
    }

    /*
     * (non-Javadoc)
     * @see net.derquinse.common.collect.Hierarchy#isRooted()
     */
    public boolean isRooted() {
        return false;
    }
}