CollectionsUtil.java

package org.rhq.enterprise.server.resource.metadata;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class CollectionsUtil {
    /**
     * Return a set containing those element that are in reference, but not in first. Both input sets are not modified
     *
     * @param  <T>
     * @param  first
     * @param  reference
     *
     * @return
     */
    static <T> Set<T> missingInFirstSet(Set<T> first, Set<T> reference) {
        Set<T> result = new HashSet<T>();

        if (reference != null) {
            // First collection is null -> everything is missing
            if (first == null) {
                result.addAll(reference);
                return result;
            }

            // else loop over the set and sort out the right items.
            for (T item : reference) {
                //                if (!first.contains(item)) {
                //                    result.add(item);
                //                }
                boolean found = false;
                Iterator<T> iter = first.iterator();
                while (iter.hasNext()) {
                    T f = iter.next();
                    if (f.equals(item)) {
                        found = true;
                        break;
                    }
                }
                if (!found)
                    result.add(item);
            }
        }

        return result;
    }

    /**
     * Return a new Set with elements that are in the first and second passed collection.
     * If one set is null, an empty Set will be returned.
     * @param  <T>    Type of set
     * @param  first  First set
     * @param  second Second set
     *
     * @return a new set (depending on input type) with elements in first and second
     */
    static <T> Set<T> intersection(Set<T> first, Set<T> second) {
        Set<T> result = new HashSet<T>();
        if ((first != null) && (second != null)) {
            result.addAll(first);
            //            result.retainAll(second);
            Iterator<T> iter = result.iterator();
            boolean found;
            while (iter.hasNext()) {
                T item = iter.next();
                found = false;
                for (T s : second) {
                    if (s.equals(item))
                        found = true;
                }
                if (!found)
                    iter.remove();
            }
        }

        return result;
    }
}