Ant example source code file (FailFast.java)

This example Ant source code file (FailFast.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Ant tags/keywords

failfast, hashset, illegalargumentexception, illegalargumentexception, iterator, map, nosuchelementexception, object, object, set, set, unsupportedoperationexception, util, weakhashmap, weakhashmap

The FailFast.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */
package org.apache.tools.ant.types.resources;

import java.util.Set;
import java.util.HashSet;
import java.util.Iterator;
import java.util.WeakHashMap;
import java.util.NoSuchElementException;
import java.util.ConcurrentModificationException;

/**
 * Helper class for ResourceCollections to return Iterators
 * that fail on changes to the object.
 * @since Ant 1.7
 */
/*package-private*/ class FailFast implements Iterator {
    private static final WeakHashMap MAP = new WeakHashMap();

    /**
     * Invalidate any in-use Iterators from the specified Object.
     * @param o the parent Object.
     */
    static synchronized void invalidate(Object o) {
        Set s = (Set) (MAP.get(o));
        if (s != null) {
            s.clear();
        }
    }

    private static synchronized void add(FailFast f) {
        Set s = (Set) (MAP.get(f.parent));
        if (s == null) {
            s = new HashSet();
            MAP.put(f.parent, s);
        }
        s.add(f);
    }

    private static synchronized void remove(FailFast f) {
        Set s = (Set) (MAP.get(f.parent));
        if (s != null) {
            s.remove(f);
        }
    }

    private static synchronized void failFast(FailFast f) {
        Set s = (Set) (MAP.get(f.parent));
        if (!s.contains(f)) {
            throw new ConcurrentModificationException();
        }
    }

    private Object parent;
    private Iterator wrapped;

    /**
     * Construct a new FailFast Iterator wrapping the specified Iterator
     * and dependent upon the specified parent Object.
     * @param o the parent Object.
     * @param i the wrapped Iterator.
     */
    FailFast(Object o, Iterator i) {
        if (o == null) {
            throw new IllegalArgumentException("parent object is null");
        }
        if (i == null) {
            throw new IllegalArgumentException("cannot wrap null iterator");
        }
        parent = o;
        if (i.hasNext()) {
            wrapped = i;
            add(this);
        }
    }

    /**
     * Fulfill the Iterator contract.
     * @return true if there are more elements.
     */
    public boolean hasNext() {
        if (wrapped == null) {
            return false;
        }
        failFast(this);
        return wrapped.hasNext();
    }

    /**
     * Fulfill the Iterator contract.
     * @return the next element.
     * @throws NoSuchElementException if no more elements.
     */
    public Object next() {
        if (wrapped == null || !wrapped.hasNext()) {
            throw new NoSuchElementException();
        }
        failFast(this);
        try {
            return wrapped.next();
        } finally {
            if (!wrapped.hasNext()) {
                wrapped = null;
                remove(this);
            }
        }
    }

    /**
     * Fulfill the Iterator contract.
     * @throws UnsupportedOperationException always.
     */
    public void remove() {
        throw new UnsupportedOperationException();
    }

}