Java Iterable First first(final Iterable iter)

Description

first

License

Apache License

Parameter

Parameter	Description
T	a parameter
iter	a parameter

Return

the first element if available, null otherwise

Declaration

public static <T> T first(final Iterable<T> iter) 

Method Source Code

//package com.java2s;
/**//from w  w w . ja v a 2s . c o m
 * Copyright 2010 Molindo GmbH
 *
 * 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.
 */

import java.util.Iterator;

import java.util.NoSuchElementException;

public class Main {
    public static final Iterator<?> EMPTY_ITERATOR = new Iterator<Object>() {

        @Override
        public boolean hasNext() {
            return false;
        }

        @Override
        public Object next() {
            throw new NoSuchElementException();
        }

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

    };

    /**
     * 
     * @param <T>
     * @param iter
     * @return the first element if available, <code>null</code> otherwise
     */
    public static <T> T first(final Iterable<T> iter) {
        return iter == null ? null : next(iter.iterator());
    }

    /**
     * 
     * @param <T>
     * @param iter
     * @return the next element if available, <code>null</code> otherwise
     */
    public static <T> T next(final Iterator<T> iter) {
        return iter == null || !iter.hasNext() ? null : iter.next();
    }

    /**
     * @param <T>
     * @param iterable
     * @return {@link Iterable#iterator()} or {@link #EMPTY_ITERATOR} if null
     */
    @SuppressWarnings("unchecked")
    public static <T> Iterator<T> iterator(Iterable<T> iterable) {
        return iterable == null ? (Iterator<T>) EMPTY_ITERATOR : iterable.iterator();
    }
}

Related

1. equal(Iterable first, Iterable second)
2. first(final Iterable iterable)
3. first(Iterable iterable)
4. first(Iterable i)
5. first(Iterable iterable)
6. first(Iterable iterable)