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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<T> implements Iterator<T> {
public final void remove() {
throw new UnsupportedOperationException();
}
}
// we need to run on JDK 1.4
private static final Iterator EMPTY = Collections.EMPTY_LIST.iterator();
public static <T> Iterator<T> empty() {
return EMPTY;
}
public static <T> Iterator<T> singleton(T value) {
return new Singleton<T>(value);
}
/**
* {@link Iterator} that returns a single (or no) value.
*/
static final class Singleton<T> extends ReadOnly<T> {
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<T,U> extends ReadOnly<T> {
private final Iterator<? extends U> core;
public Adapter(Iterator<? extends U> 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<T>} function and then iterate all
* the resulting T.
*/
public static abstract class Map<T,U> extends ReadOnly<T> {
private final Iterator<? extends U> core;
private Iterator<? extends T> current;
protected Map(Iterator<? extends U> 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<? extends T> apply(U u);
}
/**
* Filter out objects from another iterator.
*/
public static abstract class Filter<T> extends ReadOnly<T> {
private final Iterator<? extends T> core;
private T next;
protected Filter(Iterator<? extends T> 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<T> extends Filter<T> {
private Set<T> values = new HashSet<T>();
public Unique(Iterator<? extends T> core) {
super(core);
}
protected boolean matches(T value) {
return values.add(value);
}
}
/**
* Union of two iterators.
*/
public static final class Union<T> extends ReadOnly<T> {
private final Iterator<? extends T> first,second;
public Union(Iterator<? extends T> first, Iterator<? extends T> 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<T> extends ReadOnly<T> {
private final T[] items;
private int index=0;
public Array(T[] items) {
this.items = items;
}
public boolean hasNext() {
return index<items.length;
}
public T next() {
return items[index++];
}
}
}