YsCollections.java

package com.yoursway.utils;

import static com.google.common.collect.Lists.newArrayList;

import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import com.google.common.collect.Iterators;

public class YsCollections {
    
    public static <T> boolean addIfNotNull(Collection<? super T> collection, T item) {
        if (item != null)
            return collection.add(item);
        else
            return false;
    }

    public static <T> Iterable<T> forEnumeration(Enumeration<T> enumeration) {
        return YsCollections.forIterator(Iterators.forEnumeration(enumeration));
    }

    public static <T> Iterable<T> forIterator(final Iterator<T> iterator) {
        return new Iterable<T>() {
            
            private boolean used = false;
    
            public Iterator<T> iterator() {
                if (used)
                    throw new IllegalStateException("Cannot obtain this iterable's iterator twice");
                used = true;
                return iterator;
            }
            
        };
    }

    public static <T extends Comparable<? super T>> List<T> sort(Iterable<T> iterable) {
        return YsCollections.sort(iterable.iterator());
    }

    public static <T extends Comparable<? super T>> List<T> sort(Iterator<T> iterator) {
        List<T> list = newArrayList(iterator);
        Collections.sort(list);
        return list;
    }
    
    public static <K, V> Map<K, V> immutableMap(Map<? extends K, ? extends V> map) {
    	if (map.isEmpty())
    		return Collections.emptyMap();
    	else
    		return Collections.unmodifiableMap(new HashMap<K, V>(map));
    }
    
}