Mega Code Archive
Ordered Map
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import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* This is a simple Map implementation backed by a List of Map.Entry objects.
* It has the property that iterators return entries in the order in whick
* they were inserted.
*
* Operations involving searching, including get() and put(), have cost linear
* to the size of the map. In other words, avoid this implementation if your
* Map might get large.
*
* If we could assume Java 1.4+, we'd just use java.util.LinkedHashMap
* instead of this class. But we can't.
*
* @author Mike Williams
*/
public class OrderedMap extends AbstractMap {
private Set _entrySet = new OrderedSet();
public Set entrySet() {
return _entrySet;
}
public Object put(Object key, Object value) {
Entry existingEntry = getEntryWithKey(key);
if (existingEntry == null) {
entrySet().add(new Entry(key, value));
return null;
}
Object previousValue = existingEntry.getValue();
existingEntry.setValue(value);
return previousValue;
}
private Entry getEntryWithKey(Object key) {
Iterator i = entrySet().iterator();
while (i.hasNext()) {
Entry e = (Entry) i.next();
if (eq(e.getKey(), key)) {
return e;
}
}
return null;
}
static class OrderedSet extends AbstractSet {
private List _elementList = new LinkedList();
public int size() {
return _elementList.size();
}
public Iterator iterator() {
return _elementList.iterator();
}
public boolean add(Object o) {
_elementList.add(o);
return true;
}
}
static class Entry implements Map.Entry {
Object _key;
Object _value;
public Entry(Object key, Object value) {
_key = key;
_value = value;
}
public Object getKey() {
return _key;
}
public Object getValue() {
return _value;
}
public Object setValue(Object value) {
Object oldValue = _value;
_value = value;
return oldValue;
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
Map.Entry e = (Map.Entry) o;
return eq(_key, e.getKey()) && eq(_value, e.getValue());
}
public int hashCode() {
return ((_key == null) ? 0 : _key.hashCode()) ^
((_value == null) ? 0 : _value.hashCode());
}
public String toString() {
return _key + "=" + _value;
}
}
private static boolean eq(Object o1, Object o2) {
return (o1 == null ? o2 == null : o1.equals(o2));
}
}
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