Key.java

/**
 * Copyright 2013 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 io.neba.core.util;

import java.util.Arrays;

import static org.apache.commons.lang.StringUtils.join;

/**
 * A key based on multiple values, e.g. for use as a key
 * in a {@link java.util.HashMap}.
 * 
 * @author Olaf Otto
 */
public class Key {
    private static final int CONSTANT = 97;
    private static final int NULL_HASH_CODE = "null".hashCode();
    private int hashCode = 29;
    private final Object[] contents;

    public static Key toKey(Object... contents) {
        return new Key(contents);
    }

    /**
     * @param contents can be <code>null</code> and can contain <code>null</code> elements.
     */
    public Key(Object... contents) {
        this.contents = contents;
        if (contents != null && contents.length != 0) {
            for (Object content : contents) {
                hashCode = hashCode * CONSTANT + (content == null ? NULL_HASH_CODE : content.hashCode());
            }
        } else {
            hashCode =  hashCode * CONSTANT + NULL_HASH_CODE;
        }
    }

    @Override
    public int hashCode() {
        return this.hashCode;
    }
    
    @Override
    public boolean equals(Object obj) {
        return obj == this || obj != null && obj.getClass() == getClass() 
        								  && Arrays.equals(this.contents, ((Key) obj).contents);
    }

    @Override
    public String toString() {
        return "Key {" + join(this.contents, ", ") + '}';
    }
}