org.opentripplanner.netex.loader.util.AbstractHierarchicalMap Maven / Gradle / Ivy
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package org.opentripplanner.netex.loader.util;
/**
* Base class for a hierarchical map. This class proved a way to create a hierarchy of maps with
* a parent - child relationship. Elements must be added to the right level (map instance), but
* when retrieving values({@link #lookup(Object)}) the lookup call check the current instance, then
* ask the parent. This continue until the root of the hierarchy is reached. If a {@code key}
* exist in more than two places in the hierarchy, the first value found wins.
*
* There is no reference from the parent to the child, enableing garbage collection of children,
* when not referenced by the outer context any more.
*
* @param The key type
* @param Thr value type
*/
public abstract class AbstractHierarchicalMap implements ReadOnlyHierarchicalMap {
private final AbstractHierarchicalMap parent;
AbstractHierarchicalMap(AbstractHierarchicalMap parent) {
this.parent = parent;
}
/**
* Lookup element, if not found delegate up to the parent.
* NB! elements of this class and its parents are NOT merged, the closest win.
* @return an empty collection if no element are found.
*/
public V lookup(K key) {
return (localContainsKey(key) || isRoot()) ? localGet(key) : parent.lookup(key);
}
/**
* The key exist in this Collection or one of the parents (parent, parent´s parent and so on)
*/
public boolean containsKey(K key) {
return localContainsKey(key) || parentContainsKey(key);
}
/** Get value from 'local' map, parent is not queried. */
abstract V localGet(K key);
/** Check if key exist in 'local' map, parent is not queried. */
abstract boolean localContainsKey(K key);
/* private methods */
/** Return true if this instance have a parent. */
private boolean isRoot() {
return parent == null;
}
/**
* Return true if the {@code key} exist in one of the
* parents (parent, parent´s parent and so on).
*/
private boolean parentContainsKey(K key) {
return parent != null && parent.containsKey(key);
}
}