/*
* 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.util.iterator;
import java.util.*;
/**
* RandomOrderIterator - Reorders the elements returned by an Iterator.
*/
public class RandomOrderIterator<T> extends WrappedIterator<T> {
private Random rnd = new Random();
private Object buffer[];
// one more than the index of the last non-null element.
int top;
/**
* Wrap the base iterator, randomizing with a buffer of length sz.
*/
public RandomOrderIterator(int sz, Iterator<T> base) {
super(base);
buffer = new Object[sz];
top = 0;
fill();
}
@Override
public boolean hasNext() {
return top > 0;
}
@Override
public T next() {
int ix = rnd.nextInt(top);
Object rslt = buffer[ix];
top--;
buffer[ix] = buffer[top];
fill();
@SuppressWarnings("unchecked")
T obj = (T)rslt;
return obj ;
}
@Override
public void remove() {
throw new UnsupportedOperationException("randomizing does not allow modification");
}
private void fill() {
while ( top < buffer.length && super.hasNext() ) {
buffer[top++] = super.next();
}
}
}