org.opentripplanner.netex.index.hierarchy.HierarchicalElement Maven / Gradle / Ivy
package org.opentripplanner.netex.index.hierarchy;
import javax.annotation.Nullable;
/**
* This is a hierarchical wrapper around a singe element which provide the ability to create
* parent and child relationship with fallback from the child value to the parent
* value [if the child does not have a value].
*
* There is no reference from the parent to the child, enabling garbage collection of children, when
* not referenced by the outer context any more.
*
* @param the element value type.
*/
public class HierarchicalElement {
private final HierarchicalElement parent;
private E element = null;
/** Create a root for the hierarchy */
public HierarchicalElement() {
this(null);
}
/** Create a child of the given {@code parent}. */
public HierarchicalElement(HierarchicalElement parent) {
this.parent = parent;
}
/** Return a reference to the parent. */
public HierarchicalElement parent() {
return parent;
}
/**
* Get element, if not found delegate up to the parent.
*
* @return an {@code null} if no element is found.
*/
@Nullable
public E get() {
if (element != null) {
return element;
}
if (parent == null) {
return null;
} else {
return parent.get();
}
}
/**
* Set the {@code element} on the level in the hierarchy represented by {@code this} instance.
*/
public void set(E element) {
this.element = element;
}
@Override
public String toString() {
E value = get();
return value == null ? "[empty]" : value.toString();
}
}