Refactor List and Tree

src/BodyForceTreeMap.java

@@ -105,3 +105,50 @@ public class BodyForceTreeMap {
         return toString(root);
     }
 }
+
+class BodyForceTreeMapItem {
+    private final Body key;
+    private Vector3 value;
+    private BodyForceTreeMapItem parent;
+    private BodyForceTreeMapItem left;
+    private BodyForceTreeMapItem right;
+
+    public BodyForceTreeMapItem(Body key, Vector3 value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    public Body key() {
+        return this.key;
+    }
+
+    public void setValue(Vector3 value) {
+        this.value = value;
+    }
+
+    public Vector3 value() {
+        return this.value;
+    }
+
+    public BodyForceTreeMapItem left() {
+        return this.left;
+    }
+
+    public BodyForceTreeMapItem right() {
+        return this.right;
+    }
+
+    public BodyForceTreeMapItem parent() {
+        return this.parent;
+    }
+
+    public void setLeft(BodyForceTreeMapItem left) {
+        this.left = left;
+        if (left != null) left.parent = this;
+    }
+
+    public void setRight(BodyForceTreeMapItem right) {
+        this.right = right;
+        if (right != null) right.parent = this;
+    }
+}