Filter an Collection using an Predicate instance. Example: The sample below is going to return a Collection that inside of it, it'll have just a single instance of a String "A Object". - Java java.util

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Description

Filter an Collection using an Predicate instance. Example: The sample below is going to return a Collection that inside of it, it'll have just a single instance of a String "A Object".

Demo Code


import java.util.ArrayList;
import java.util.Collection;
import java.util.function.Predicate;

public class Main {
  /**/* w w w.  j  av a  2  s.  co m*/
   * Filter an {@link Collection} using an {@link Predicate} instance.<br/>
   * Example: The sample below is going to return a {@link Collection} that inside
   * of it, it'll have just a single instance of a String "A Object".
   * 
   * <pre>
   * {@link ArrayList}&lt;String&gt; list = new ArrayList&lt;String&gt;();
   * list.add(&quot;A Object&quot;);
   * list.add(&quot;B Object&quot;);
   * 
   * {@link Collection}&lt;String&gt; b = CollectionsUtils.filter(list, new {@link Predicate}&lt;String&gt;() {
   * 
   *    public boolean apply(String type) {
   *       return (type.charAt(0) == 'A');
   *    };
   * });
   * </pre>
   * 
   * @param source
   *          Collection source to be filtered. This field is mandatory, if you
   *          don't send it, it'll generate an {@link NullPointerException}.
   * @param predicate
   *          Instance of the predicate to be used to apply the filter. This field
   *          is mandatory, if you don't send it, it'll generate an
   *          {@link NullPointerException}.
   * @return It'll returns an Collection instance filtered by the predicate. If
   *         the <code>source</code> or the <code>predicate</code> passed through
   *         parameter is null, it'll throw a {@link NullPointerException}.
   */
  public static <T> Collection<T> filter(Collection<T> source, Predicate<T> predicate) {
    if (source == null) {
      throw new NullPointerException("The source is mandatory.");
    }
    if (predicate == null) {
      throw new NullPointerException("The predicate is mandatory.");
    }

    Collection<T> result = new ArrayList<T>();
    if (source.size() > 0) {
      for (T element : source) {
        if (predicate.test(element)) {
          result.add(element);
        }
      }
    }
    return result;
  }
}

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