src/main/java/freemarker/core/_UnmodifiableSet.java

/*
 * 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 freemarker.core;

import java.util.AbstractSet;

/** Don't use this; used internally by FreeMarker, might changes without notice. */
public abstract class _UnmodifiableSet<E> extends AbstractSet<E> {

    @Override
    public boolean add(E o) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean remove(Object o) {
        if (contains(o)) {
            throw new UnsupportedOperationException();
        }
        return false;
    }

    @Override
    public void clear() {
        if (!isEmpty()) {
            throw new UnsupportedOperationException();
        }
    }

}