Create a typesafe view over an underlying raw set.
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import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
public class Utils {
/**
* Create a typesafe view over an underlying raw set.
* Mutations affect the underlying set (this is not a copy).
* {@link Set#clear} will make the view empty but may not clear the underlying set.
* You may add elements only of the requested type.
* {@link Set#contains} also performs a type check and will throw {@link ClassCastException}
* for an illegal argument.
* The view is serializable if the underlying set is.
* @param rawSet an unchecked set
* @param type the desired element type
* @param strict if false, elements in the underlying set which are not null and which are not assignable
* to the requested type are omitted from the view;
* if true, a {@link ClassCastException} may arise during some set operation
* @return a view over the raw set guaranteed to match the specified type
*/
public static <E> Set<E> checkedSetByFilter(Set rawSet, Class<E> type, boolean strict) {
return new CheckedSet<E>(rawSet, type, strict);
}
private static final class CheckedSet<E> extends AbstractSet<E> implements Serializable {
private static final long serialVersionUID = 1L;
private final Set rawSet;
private final Class<E> type;
private final boolean strict;
public CheckedSet(Set rawSet, Class<E> type, boolean strict) {
this.rawSet = rawSet;
this.type = type;
this.strict = strict;
}
private boolean acceptEntry(Object o) {
if (o == null) {
return true;
} else if (type.isInstance(o)) {
return true;
} else if (strict) {
throw new ClassCastException(o + " was not a " + type.getName()); // NOI18N
} else {
return false;
}
}
@Override
public Iterator<E> iterator() {
return new CheckedIterator<E>(rawSet.iterator()) {
@Override
protected boolean accept(Object o) {
return acceptEntry(o);
}
};
}
@Override
public int size() {
int c = 0;
Iterator it = rawSet.iterator();
while (it.hasNext()) {
if (acceptEntry(it.next())) {
c++;
}
}
return c;
}
@Override
@SuppressWarnings("unchecked") // complains about usage of raw set
public boolean add(E o) {
return rawSet.add(type.cast(o));
}
@Override
public boolean contains(Object o) {
return rawSet.contains(type.cast(o));
}
}
}
abstract class CheckedIterator<E> implements Iterator<E> {
static final Object WAITING = new Object();
private final Iterator it;
private Object next = WAITING;
public CheckedIterator(Iterator it) {
this.it = it;
}
protected abstract boolean accept(Object o);
public boolean hasNext() {
if (next != WAITING) {
return true;
}
while (it.hasNext()) {
next = it.next();
if (accept(next)) {
return true;
}
}
next = WAITING;
return false;
}
public E next() {
if (next == WAITING && !hasNext()) {
throw new NoSuchElementException();
}
assert next != WAITING;
@SuppressWarnings("unchecked")
// type-checking is done by accept()
E x = (E) next;
next = WAITING;
return x;
}
public void remove() {
it.remove();
}
}
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