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package org.apache.commons.collections.collection;

import java.util.Collection;
import java.util.Iterator;

import org.apache.commons.collections.Predicate;

/**
 * Decorates another <code>Collection</code> to validate that additions
 * match a specified predicate.
 * <p>
 * If an object cannot be added to the collection, an IllegalArgumentException
 * is thrown.
 *
 * @since Commons Collections 3.0
 * @version $Revision: 3330 $ $Date: 2006-03-14 09:47:58 +0100 (Di, 14 Mrz 2006) $
 * 
 * @author Stephen Colebourne
 * @author Paul Jack
 */
public class PredicatedCollection extends AbstractCollectionDecorator {

    /** The predicate to use */
    protected final Predicate predicate;

    /**
     * Factory method to create a predicated (validating) collection.
     * <p>
     * If there are any elements already in the collection being decorated, they
     * are validated.
     * 
     * @param coll  the collection to decorate, must not be null
     * @param predicate  the predicate to use for validation, must not be null
     * @throws IllegalArgumentException if collection or predicate is null
     * @throws IllegalArgumentException if the collection contains invalid elements
     */
    public static Collection decorate(Collection coll, Predicate predicate) {
        return new PredicatedCollection(coll, predicate);
    }
    
    //-----------------------------------------------------------------------
    /**
     * Constructor that wraps (not copies).
     * <p>
     * If there are any elements already in the collection being decorated, they
     * are validated.
     * 
     * @param coll  the collection to decorate, must not be null
     * @param predicate  the predicate to use for validation, must not be null
     * @throws IllegalArgumentException if collection or predicate is null
     * @throws IllegalArgumentException if the collection contains invalid elements
     */
    protected PredicatedCollection(Collection coll, Predicate predicate) {
        super(coll);
        if (predicate == null) {
            throw new IllegalArgumentException("Predicate must not be null");
        }
        this.predicate = predicate;
        for (Iterator it = coll.iterator(); it.hasNext(); ) {
            validate(it.next());
        }
    }

    /**
     * Validates the object being added to ensure it matches the predicate.
     * <p>
     * The predicate itself should not throw an exception, but return false to
     * indicate that the object cannot be added.
     * 
     * @param object  the object being added
     * @throws IllegalArgumentException if the add is invalid
     */
    protected void validate(Object object) {
        if (predicate.evaluate(object) == false) {
            throw new IllegalArgumentException("Cannot add Object '" + object + "' - Predicate rejected it");
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Override to validate the object being added to ensure it matches
     * the predicate.
     * 
     * @param object  the object being added
     * @return the result of adding to the underlying collection
     * @throws IllegalArgumentException if the add is invalid
     */
    public boolean add(Object object) {
        validate(object);
        return getCollection().add(object);
    }

    /**
     * Override to validate the objects being added to ensure they match
     * the predicate. If any one fails, no update is made to the underlying
     * collection.
     * 
     * @param coll  the collection being added
     * @return the result of adding to the underlying collection
     * @throws IllegalArgumentException if the add is invalid
     */
    public boolean addAll(Collection coll) {
        for (Iterator it = coll.iterator(); it.hasNext(); ) {
            validate(it.next());
        }
        return getCollection().addAll(coll);
    }

}
