Java Collection Unique getUnique(Collection collection)

Description

Returns the only element in the given collection.

License

Apache License

Parameter

Parameter	Description
collection	The collection of elements that is expected to be of size 1.

Exception

Parameter	Description
IllegalStateException	If the collection size is different from 1.

Return

The only element in the collection.

Declaration

public static <T> T getUnique(Collection<T> collection) 

Method Source Code

//package com.java2s;
/*/*from   w  ww  .  j a  v  a2s  .com*/
 * Entwined STM
 * 
 * (c) Copyright 2013 CERN. This software is distributed under the terms of the Apache License Version 2.0, copied
 * verbatim in the file "COPYING". In applying this licence, CERN does not waive the privileges and immunities granted
 * to it by virtue of its status as an Intergovernmental Organization or submit itself to any jurisdiction.
 */

import java.util.Collection;

public class Main {
    /**
     * Returns the only element in the given collection.
     * 
     * @param collection The collection of elements that is expected to be of size 1.
     * @return The only element in the collection.
     * @throws IllegalStateException If the collection size is different from 1.
     */
    public static <T> T getUnique(Collection<T> collection) {
        checkNull("Collection", collection);
        if (collection.size() != 1) {
            throw new IllegalArgumentException(
                    "Collection " + collection + " is expected to contain only one element");
        }
        return collection.iterator().next();
    }

    /**
     * A facility method that checks object to be null and throws the {@link IllegalArgumentException} if it is. This
     * method can be chained as it returns the value in case of success.
     * 
     * @param <T> Type of the checked and returned value.
     * @param name The object's name.
     * @param value The object.
     * @return The passed object.
     */
    public static <T> T checkNull(String name, T value) {
        if (null == value) {
            throw new IllegalArgumentException(name + " can't be null");
        }
        return value;
    }

    /**
     * A facility method that checks object to be null and throws the {@link IllegalArgumentException} if it is. This
     * method can be chained as it returns the value in case of success.
     * 
     * @param name The object's name.
     * @param value The object.
     * @return The passed value string in case of success.
     */
    public static String checkNull(String name, String value) {
        if (null == value) {
            throw new IllegalArgumentException(name + " can't be null");
        }
        if (value.trim().length() == 0) {
            throw new IllegalArgumentException(name + " can't be empty or be constituted only of spaces");
        }
        return value;
    }
}

Related

1. addUnique(C collection, T item)
2. addUnique(final Collection collection, final Object value)
3. generateUniqueName(String aName, Collection aStringCollection)
4. getUnique(Collection c)
5. getUniqueName(String name, Collection collection)
6. getUniqueNameWithNumbers(Collection names, String baseName)
7. getUniqueValue(Collection values, String initValue)
8. hasUniqueObject(Collection collection)