Mega Code Archive
Create a typesafe view over an underlying raw map
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import java.io.Serializable;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Map;
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 map.
* Mutations affect the underlying map (this is not a copy).
* {@link Map#clear} will make the view empty but may not clear the underlying map.
* You may add entries only of the requested type pair.
* {@link Map#get}, {@link Map#containsKey}, and {@link Map#containsValue} also perform a type check
* and will throw {@link ClassCastException} for an illegal argument.
* The view is serializable if the underlying map is.
* @param rawMap an unchecked map
* @param keyType the desired entry key type
* @param valueType the desired entry value type
* @param strict if false, entries in the underlying map for which the key is not null but not assignable
* to the requested key type, and/or the value is not null but not assignable to
* the requested value type, are omitted from the view;
* if true, a {@link ClassCastException} may arise during some map operation
* @return a view over the raw map guaranteed to match the specified type
*/
public static <K,V> Map<K,V> checkedMapByFilter(Map rawMap, Class<K> keyType, Class<V> valueType, boolean strict) {
return new CheckedMap<K,V>(rawMap, keyType, valueType, strict);
}
private static final class CheckedMap<K,V> extends AbstractMap<K,V> implements Serializable {
private static final long serialVersionUID = 1L;
private final Map rawMap;
private final Class<K> keyType;
private final Class<V> valueType;
private final boolean strict;
public CheckedMap(Map rawMap, Class<K> keyType, Class<V> valueType, boolean strict) {
this.rawMap = rawMap;
this.keyType = keyType;
this.valueType = valueType;
this.strict = strict;
}
private boolean acceptKey(Object o) {
if (o == null) {
return true;
} else if (keyType.isInstance(o)) {
return true;
} else if (strict) {
throw new ClassCastException(o + " was not a " + keyType.getName()); // NOI18N
} else {
return false;
}
}
private boolean acceptValue(Object o) {
if (o == null) {
return true;
} else if (valueType.isInstance(o)) {
return true;
} else if (strict) {
throw new ClassCastException(o + " was not a " + valueType.getName()); // NOI18N
} else {
return false;
}
}
private boolean acceptEntry(Map.Entry e) {
return acceptKey(e.getKey()) && acceptValue(e.getValue());
}
private final class EntrySet extends AbstractSet<Map.Entry<K, V>> {
@Override
public Iterator<Map.Entry<K,V>> iterator() {
return new CheckedIterator<Map.Entry<K,V>>(rawMap.entrySet().iterator()) {
@Override
protected boolean accept(Object o) {
return acceptEntry((Map.Entry) o);
}
};
}
@Override
public int size() {
int c = 0;
Iterator it = rawMap.entrySet().iterator();
while (it.hasNext()) {
if (acceptEntry((Map.Entry) it.next())) {
c++;
}
}
return c;
}
}
@Override
public Set<Map.Entry<K, V>> entrySet() {
return new EntrySet();
}
@Override
public V get(Object key) {
Object o = rawMap.get(keyType.cast(key));
if (acceptValue(o)) {
@SuppressWarnings("unchecked")
V v = (V) o;
return v;
} else {
return null;
}
}
@SuppressWarnings("unchecked")
@Override
public V put(K key, V value) {
Object old = rawMap.put(keyType.cast(key), valueType.cast(value));
if (acceptValue(old)) {
return (V) old;
} else {
return null;
}
}
@Override
public V remove(Object key) {
Object old = rawMap.remove(keyType.cast(key));
if (acceptValue(old)) {
@SuppressWarnings("unchecked")
V v = (V) old;
return v;
} else {
return null;
}
}
@Override
public boolean containsKey(Object key) {
return rawMap.containsKey(keyType.cast(key)) &&
acceptValue(rawMap.get(key));
}
@Override
public boolean containsValue(Object value) {
// Cannot just ask rawMap since we could not check type of key.
return super.containsValue(valueType.cast(value));
}
@Override
public int size() {
int c = 0;
Iterator it = rawMap.entrySet().iterator();
while (it.hasNext()) {
if (acceptEntry((Map.Entry) it.next())) {
c++;
}
}
return c;
}
// keySet, values cannot be so easily overridden because we type-check whole entries
}
}
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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