com.sun.xml.xsom.impl.scd.Iterators Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2022 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package com.sun.xml.xsom.impl.scd;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.HashSet;
import java.util.Collections;
/**
* Various convenient {@link Iterator} implementations.
* @author Kohsuke Kawaguchi
*/
public class Iterators {
static abstract class ReadOnly implements Iterator {
public final void remove() {
throw new UnsupportedOperationException();
}
}
public static Iterator empty() {
return Collections.emptyIterator();
}
public static Iterator singleton(T value) {
return new Singleton<>(value);
}
/**
* {@link Iterator} that returns a single (or no) value.
*/
static final class Singleton extends ReadOnly {
private T next;
Singleton(T next) {
this.next = next;
}
public boolean hasNext() {
return next!=null;
}
public T next() {
T r = next;
next = null;
return r;
}
}
/**
* {@link Iterator} that wraps another {@link Iterator} and changes its type.
*/
public static abstract class Adapter extends ReadOnly {
private final Iterator core;
public Adapter(Iterator core) {
this.core = core;
}
public boolean hasNext() {
return core.hasNext();
}
public T next() {
return filter(core.next());
}
protected abstract T filter(U u);
}
/**
* For each U, apply {@code U->Iterator} function and then iterate all
* the resulting T.
*/
public static abstract class Map extends ReadOnly {
private final Iterator core;
private Iterator current;
protected Map(Iterator core) {
this.core = core;
}
public boolean hasNext() {
while(current==null || !current.hasNext()) {
if(!core.hasNext())
return false; // nothing more to enumerate
current = apply(core.next());
}
return true;
}
public T next() {
return current.next();
}
protected abstract Iterator apply(U u);
}
/**
* Filter out objects from another iterator.
*/
public static abstract class Filter extends ReadOnly {
private final Iterator core;
private T next;
protected Filter(Iterator core) {
this.core = core;
}
/**
* Return true to retain the value.
*/
protected abstract boolean matches(T value);
public boolean hasNext() {
while(core.hasNext() && next==null) {
next = core.next();
if(!matches(next))
next = null;
}
return next!=null;
}
public T next() {
if(next==null) throw new NoSuchElementException();
T r = next;
next = null;
return r;
}
}
/**
* Only return unique items.
*/
static final class Unique extends Filter {
private Set values = new HashSet<>();
public Unique(Iterator core) {
super(core);
}
protected boolean matches(T value) {
return values.add(value);
}
}
/**
* Union of two iterators.
*/
public static final class Union extends ReadOnly {
private final Iterator first,second;
public Union(Iterator first, Iterator second) {
this.first = first;
this.second = second;
}
public boolean hasNext() {
return first.hasNext() || second.hasNext();
}
public T next() {
if(first.hasNext()) return first.next();
else return second.next();
}
}
/**
* Array iterator.
*/
public static final class Array extends ReadOnly {
private final T[] items;
private int index=0;
public Array(T[] items) {
this.items = items;
}
public boolean hasNext() {
return index