Example usage for java.util Collections emptySet

Introduction

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

Prototype

@SuppressWarnings("unchecked")
public static final <T> Set<T> emptySet()

Source Link

Document

Returns an empty set (immutable).

Usage

From source file:Main.java

/**
 * Convert a String to a unmodifiable set of characters.
 * @param str The string to convert//from w w  w  .j  a  v  a 2  s  . c o  m
 * @return A set containing the characters in str. A empty set
 *    is returned if str is null.
 */
public static Set<Character> strToUnmodifiableSet(String str) {
    if (str == null)
        return Collections.emptySet();
    if (str.length() == 1)
        return Collections.singleton(str.charAt(0));
    return Collections.unmodifiableSet(strToSet(str));
}

From source file:Main.java

private static Set<String> getQueryParameterNames(Uri uri) {
    if (uri.isOpaque()) {
        throw new UnsupportedOperationException("This isn't a hierarchical URI.");
    }/*from  w  w  w  .  ja  va  2s . c om*/

    String query = uri.getEncodedQuery();
    if (query == null) {
        return Collections.emptySet();
    }

    Set<String> names = new LinkedHashSet<String>();
    int start = 0;
    do {
        int next = query.indexOf('&', start);
        int end = (next == -1) ? query.length() : next;

        int separator = query.indexOf('=', start);
        if (separator > end || separator == -1) {
            separator = end;
        }

        String name = query.substring(start, separator);
        names.add(Uri.decode(name));

        // Move start to end of name.
        start = end + 1;
    } while (start < query.length());

    return Collections.unmodifiableSet(names);
}

From source file:Main.java

/**
 * Returns a collection with the common elements in c1 and c2
 * @param <T>//from   w  w  w  . ja  v  a  2 s.  c  om
 * @param c1
 * @param c2
 * @return
 */
public static <T> Collection<T> intersect(Collection<T> c1, Collection<T> c2) {

    if (c1.isEmpty() || c2.isEmpty()) {
        return Collections.emptySet();
    }

    if (!(c2 instanceof Set) && (c1 instanceof Set || c1.size() > c2.size())) {
        //swap
        Collection<T> tmp = c1;
        c1 = c2;
        c2 = tmp;
    }

    Collection<T> result = new HashSet<T>();
    for (T obj : c1) {
        if (c2.contains(obj)) {
            result.add(obj);
        }
    }

    return result;
}

From source file:Main.java

public static Set<String> getQueryParameterNames(Uri uri) {
    if (uri.isOpaque()) {
        throw new UnsupportedOperationException("This isn't a hierarchical URI.");
    }/* ww w  . ja v  a  2s. c om*/

    String query = uri.getEncodedQuery();
    if (query == null) {
        return Collections.emptySet();
    }

    Set<String> names = new LinkedHashSet<String>();
    int start = 0;
    do {
        int next = query.indexOf('&', start);
        int end = next == -1 ? query.length() : next;

        int separator = query.indexOf('=', start);
        if (separator > end || separator == -1) {
            separator = end;
        }

        String name = query.substring(start, separator);
        names.add(Uri.decode(name));

        // Move start to end of name.
        start = end + 1;
    } while (start < query.length());

    return Collections.unmodifiableSet(names);
}

From source file:Main.java

public static <T> Set<T> immutableSet(T... set) {
    if (set == null)
        return Collections.emptySet();
    return Collections.unmodifiableSet(new HashSet<T>(Arrays.asList(set)));
}

From source file:Main.java

/**
 * Creates an unmodifiable set filled with the given values.
 * //ww  w.  j a  v  a 2  s . co  m
 * @param <T>
 *            the set's element type.
 * @param values
 *            the values.
 * @return a newly created set containing the given values.
 */
@SafeVarargs
public static <T> Set<T> createUnmodifiableSet(final T... values) {
    switch (values.length) {
    case 0:
        return Collections.emptySet();
    case 1:
        return Collections.singleton(values[0]);
    default:
        return Collections.unmodifiableSet(createHashSet(values));
    }
}

From source file:Main.java

/**
 * Build a set of bean from the provided iterable
 * @param source any kind of iterable//  w  w w .  j av  a  2  s . c  om
 * @return a {@link Serializable} {@link Set} containing the same element set
 */
public static <Bean> Set<Bean> asSet(Iterable<Bean> source) {
    if (source instanceof Set && source instanceof Serializable) {
        return (Set<Bean>) source;
    } else if (source == null) {
        return Collections.emptySet();
    } else {
        Set<Bean> returned = new HashSet<Bean>();
        for (Bean b : source) {
            returned.add(b);
        }
        return returned;
    }
}

From source file:Main.java

public static <T> Set<T> unmodifiableSet(Set<? extends T> list) {
    if ((list == null) || (list.isEmpty())) {
        return Collections.emptySet();
    }//from   ww  w  .  j  a va  2s  . c om
    return Collections.unmodifiableSet(list);
}

From source file:Main.java

/**
 * This is a convenience method that essentially checks for a null set and returns Collections.emptySet in that
 * case. If the set is non-null, then this is an identity function.
 * //  w  w  w.  j  a v a 2s  .  c  o  m
 * @param <T>
 * @param set
 * @return
 */
public static <T> Set<T> getSetValue(Set<T> set) {
    if (set == null) {
        return Collections.emptySet();
    }

    return set;
}

From source file:Main.java

public static <T> Set<T> newSet(T... values) {
    if (values == null) {
        return Collections.emptySet();
    }/*  w w  w . j a  v  a2 s  .c om*/

    return new HashSet<T>(Arrays.asList(values));
}