/*
* 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.jena.atlas.iterator ;
import java.util.ArrayDeque ;
import java.util.Deque ;
import java.util.Iterator ;
/** An iterator where you can push items backinto the iterator, to be yielded (LIFO) next time.
* @see PeekIterator
*/
public class PushbackIterator<T> implements Iterator<T> {
private Deque<T> items = new ArrayDeque<>() ;
private Iterator<T> iter ;
public PushbackIterator(Iterator<T> iter) {
if ( iter == null )
throw new IllegalArgumentException("Wrapped iterator can't be null") ;
this.iter = iter ;
}
public void pushback(T item) {
items.push(item) ;
}
@Override
public boolean hasNext() {
if ( !items.isEmpty() )
return true ;
return iter.hasNext() ;
}
@Override
public T next() {
if ( !items.isEmpty() )
return items.pop() ;
return iter.next() ;
}
@Override
public void remove() {
// Need to track if last next() was from the stack or not.
throw new UnsupportedOperationException() ;
}
}