--- /dev/null
+import java.util.*;
+import java.lang.reflect.*;
+import org.aspectj.lang.annotation.*;
+
+ /**
+ * a generic aspect, we've used descriptive role names for the type variables
+ * (Parent and Child) but you could use anything of course
+ */
+ /*public */ abstract aspect ParentChildRelationship<Parent,Child> {
+
+ /** generic interface implemented by parents */
+ interface ParentHasChildren<C extends ChildHasParent>{
+ List<C> getChildren();
+ void addChild(C child);
+ void removeChild(C child);
+ }
+
+ /** generic interface implemented by children */
+ interface ChildHasParent<P extends ParentHasChildren>{
+ P getParent();
+ void setParent(P parent);
+ }
+
+ /** ensure the parent type implements ParentHasChildren<child type> */
+ declare parents: Parent implements ParentHasChildren<Child>;
+
+ /** ensure the child type implements ChildHasParent<parent type> */
+ declare parents: Child implements ChildHasParent<Parent>;
+
+ // Inter-type declarations made on the *generic* interface types to provide
+ // default implementations.
+
+ /** list of children maintained by parent */
+ public List<C> ParentHasChildren<C>.children = new ArrayList<C>();
+
+ /** reference to parent maintained by child */
+ public P ChildHasParent<P>.parent;
+
+ /** Default implementation of getChildren for the generic type ParentHasChildren */
+ public List<C> ParentHasChildren<C>.getChildren() {
+ return Collections.unmodifiableList(children);
+ }
+
+ /** Default implementation of getParent for the generic type ChildHasParent */
+ public P ChildHasParent<P>.getParent() {
+ return parent;
+ }
+
+ /**
+ * Default implementation of addChild, ensures that parent of child is
+ * also updated.
+ */
+ public void ParentHasChildren<C>.addChild(C child) {
+ if (child.parent != null) {
+ child.parent.removeChild(child);
+ }
+ children.add(child);
+ child.parent = this;
+ }
+
+ /**
+ * Default implementation of removeChild, ensures that parent of
+ * child is also updated.
+ */
+ public void ParentHasChildren<C>.removeChild(C child) {
+ if (children.remove(child)) {
+ child.parent = null;
+ }
+ }
+
+ /**
+ * Default implementation of setParent for the generic type ChildHasParent.
+ * Ensures that this child is added to the children of the parent too.
+ */
+ public void ChildHasParent<P>.setParent(P parent) {
+ parent.addChild(this);
+ }
+
+ /**
+ * Matches at an addChild join point for the parent type P and child type C
+ */
+ public pointcut addingChild(Parent p, Child c) :
+ execution(* Parent.addChild(Child)) && this(p) && args(c);
+
+ /**
+ * Matches at a removeChild join point for the parent type P and child type C
+ */
+ public pointcut removingChild(Parent p, Child c) :
+ execution(* Parent.removeChild(Child)) && this(p) && args(c);
+
+ }
+
+aspect GenericAspectX extends ParentChildRelationship<Top,Bottom> {
+
+ // Advice to trigger weave infos
+ before(Top p,Bottom c): ParentChildRelationship.addingChild(p,c) {}
+ before(Top p,Bottom c): ParentChildRelationship.removingChild(p,c) {}
+
+ public static void main(String []argv) {
+
+ // Check the state of top
+ Top t = new Top();
+ check(t instanceof ParentHasChildren,"Top should implement ParentHasChildren");
+ Type[] intfs = Top.class.getGenericInterfaces();
+ check(intfs[0] instanceof ParameterizedType,
+ "Expected Top to have parameterized interface but found "+intfs[0]);
+ ParameterizedType pt = (ParameterizedType) intfs[0];
+ Type[] tArgs = pt.getActualTypeArguments();
+ check(tArgs[0]==Bottom.class,
+ "Expecting Bottom parameter but found " + tArgs[0]);
+
+
+ // Check the state of top
+ Bottom b = new Bottom();
+ check(b instanceof ChildHasParent,"Bottom should implement ChildHasParent");
+ intfs = Bottom.class.getGenericInterfaces();
+ check(intfs[0] instanceof ParameterizedType,
+ "Expected Bottom to have parameterized interface but found "+intfs[0]);
+ pt = (ParameterizedType) intfs[0];
+ tArgs = pt.getActualTypeArguments();
+ check(tArgs[0]==Top.class,
+ "Expecting Top parameter but found " + tArgs[0]);
+
+
+
+
+ // Field fiddling
+ b.parent = t;
+ List<Bottom> kids = new ArrayList<Bottom>();
+ kids.add(b);
+ t.children = kids;
+
+
+ // start using the methods
+ List<Bottom> kids2 = t.getChildren();
+ check(kids2.size()==1,
+ "Expected one child of the Top but found "+kids2.size());
+ check(kids2.get(0).equals(b),
+ "Expected one child of the Top which was what we put in there!"+kids2.get(0));
+
+ // and the parent methods
+ Top retrievedParent = b.getParent();
+ check(retrievedParent==t,
+ "parent check 1 failed "+
+ "retrieved="+retrievedParent+" expected="+t);
+
+
+ Top top2 = new Top();
+ b.setParent(top2);
+ Top retrievedParent2 = b.getParent();
+ check(retrievedParent2==top2,
+ "parent check 2 failed "+
+ "retrieved="+retrievedParent2+" expected="+top2);
+
+ Top top3 = new Top();
+ Bottom bot2 = new Bottom();
+ top3.addChild(bot2);
+ Bottom aBottom = top3.getChildren().get(0);
+ check(aBottom==bot2,"Incorrect child? expected="+bot2+" found="+aBottom);
+ top3.removeChild(bot2);
+ int size=top3.getChildren().size();
+ check(size==0,"Should be no children but there were "+size);
+
+
+ }
+
+ public static void check(boolean b,String msg) {
+ if (!b) throw new RuntimeException(msg);
+ }
+}
+
+class Top {}
+class Bottom {}
+
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