Example usage for java.util Collections emptyList

Introduction

In this page you can find the example usage for java.util Collections emptyList.

Prototype

@SuppressWarnings("unchecked")
public static final <T> List<T> emptyList()

Source Link

Document

Returns an empty list (immutable).

Usage

From source file:Main.java

public static <T> List<T> nullToEmpty(List<T> list) {
    return list == null ? Collections.emptyList() : list;
}

From source file:com.ms.commons.lang.BeanUtils.java

public static <T extends Object> List<T> convert(Class<T> clazz, Collection<?> raw,
        ValueEditable... specialConverts) {
    if (Argument.isEmpty(raw)) {
        return Collections.emptyList();
    }/*from   w w w. ja  v a2 s  .c  o  m*/
    List<T> data = new ArrayList<T>(raw.size());
    for (Object obj : raw) {
        T vo;
        try {
            vo = clazz.newInstance();
            copyProperties(vo, obj, specialConverts);
            data.add(vo);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    return data;
}

From source file:Main.java

public static <T> List<T> nonNullFrom(List<T> list) {
    if (list == null || list.isEmpty()) {
        return Collections.emptyList();
    }/*from w  w w .  j  a  v a 2 s . c  o m*/
    return Collections.unmodifiableList(list);
}

From source file:Main.java

public static <T> List<T> readList(String root, String filename, Class<T> type) {
    List<T> objects = new ArrayList<>();
    File file = new File(root, filename);
    try {/*ww w. j a va 2 s  .  c  o  m*/
        if (file.exists()) {
            FileInputStream fis = new FileInputStream(file);
            ObjectInputStream ois = new ObjectInputStream(fis);
            Object object = ois.readObject();
            if (object instanceof List) {
                for (Object it : (List) object) {
                    objects.add(type.cast(it));
                }
            }
            ois.close();
            return Collections.unmodifiableList(objects);
        }
    } catch (Exception e) {
        Log.e(TAG, String.format("Failed to read [%s]", file), e);
    }
    return Collections.emptyList();
}

From source file:Main.java

/**
 * Using like subList() but it take randoms elements.
 *
 * @param list/*  w  ww  .j  av  a 2  s.  c om*/
 * @param sizeOfSubList
 */
public static <E> void randomSubList(List<E> list, int sizeOfSubList) {
    List<E> subList = Collections.emptyList();
    if (isNotEmpty(list) && list.size() > sizeOfSubList) {
        subList = new ArrayList<E>(sizeOfSubList);
        Random generator = new Random();
        for (int i = 0; i < sizeOfSubList; i++) {
            int random = generator.nextInt(list.size());
            subList.add(list.get(random));
            list.remove(random);
        }
    }
    list.clear();
    list.addAll(subList);
}

From source file:Main.java

/**
 * @param list//  w w w.  j av a 2s .com
 * @param splitSize
 * @return splited collection
 */
public static <T> List<List<T>> split(List<T> list, int splitSize) {
    if (list == null || list.isEmpty() || splitSize <= 0) {
        return Collections.emptyList();
    }

    List<List<T>> result = new ArrayList<List<T>>();
    if (list.size() > splitSize) {
        int fromIndex = 0;
        while (true) {
            int toIndex = fromIndex + splitSize;
            if (toIndex > list.size()) {
                toIndex = list.size();
            }
            result.add(list.subList(fromIndex, toIndex));
            fromIndex += splitSize;
            if (fromIndex >= list.size()) {
                break;
            }
        }
    } else {
        result.add(list);
    }

    return result;
}

From source file:Main.java

/**
 * Copies the contents of a List to a new, unmodifiable List.  If the List is null, an empty List will be returned.
 * <p>// w w  w .  j  a va  2  s .c o  m
 * This is especially useful for methods which take List parameters.  Directly assigning such a List to a member
 * variable can allow external classes to modify internal state.  Classes may have different state depending on the
 * size of a List; for example, a button might be disabled if the the List size is zero.  If an external object
 * can change the List, the containing class would have no way have knowing a modification occurred.
 * 
 * @param <T> The type of element in the List.
 * @param list The List to copy.
 * @return A new, unmodifiable List which contains all of the elements of the List parameter.  Will never be null.
 */
public static <T> List<T> copyToUnmodifiableList(List<T> list) {
    if (list != null) {
        List<T> listCopy = new ArrayList(list);
        return Collections.unmodifiableList(listCopy);
    } else {
        return Collections.emptyList();
    }
}

From source file:Main.java

/**
 * Wraps a possibly null list in an immutable wrapper.
 *
 * @param <T>    the type parameter
 * @param source Nullable list to wrap.// www .  jav  a2  s  .co  m
 * @return {@link Collections#unmodifiableList(List)} if given list is not null, otherwise {@link java.util.Collections#EMPTY_LIST}.
 */
public static <T> List<T> wrap(final List<T> source) {
    if (source != null) {
        return Collections.unmodifiableList(source);
    }
    return Collections.emptyList();
}

From source file:com.navercorp.pinpoint.common.server.util.InetAddressUtils.java

public static List<InetAddress> toInetAddressList(List<String> addressList) {
    if (CollectionUtils.isEmpty(addressList)) {
        return Collections.emptyList();
    }/*from  w  w w.ja  va  2 s  .  c o  m*/
    final List<InetAddress> inetAddressList = new ArrayList<InetAddress>(addressList.size());
    for (String ignoreAddress : addressList) {
        if (StringUtils.isBlank(ignoreAddress)) {
            continue;
        }
        // not throw UnknownHostException
        final InetAddress address = InetAddresses.forString(ignoreAddress);
        if (address != null) {
            inetAddressList.add(address);
        }
    }
    return inetAddressList;
}

From source file:Main.java

/**
 * Given two collections of elements of type <T>, return a collection containing the items from both lists
 * //from   ww w .ja  v a2 s  .  c o  m
 * @param <T>
 *            Type
 * @param collection1
 *            Collection #1
 * @param collection2
 *            Collection #2
 * @return Collection with items from both lists
 */
public static <T> Collection<T> union(Collection<? extends T> collection1,
        Collection<? extends T> collection2) {
    if (isEmpty(collection1)) {
        if (isEmpty(collection2)) {
            // if both are empty, return empty list
            return Collections.emptyList();
        }
        // if just 1 is empty, return 2
        return new ArrayList<T>(collection2);
    }
    // at this point when know 1 is not empty
    if (isEmpty(collection2)) {
        // so if 2 is, return 1.
        return new ArrayList<T>(collection1);
    }

    // we know both 1 and 2 aren't empty
    Set<T> union = new HashSet<T>(collection1.size() + collection2.size());

    union.addAll(collection1);
    union.addAll(collection2);

    return new ArrayList<T>(union);
}