Define template contract

src/main/java/org/ical4j/template/AbstractTemplate.java

@@ -1,14 +1,15 @@
 package org.ical4j.template;
 
 import java.lang.reflect.InvocationTargetException;
-import java.util.function.UnaryOperator;
 
 /**
- * Base class for templates with the added ability to construct new object instances.
+ * Base class for templates with support for a prototype instance. A prototype is an
+ * instance of the applicable object type used to construct a new instance or modify
+ * an existing instance prior to applying the template.
  *
- * @param <T>
+ * @param <T> the applicable object type
  */
-public abstract class AbstractTemplate<T> implements UnaryOperator<T> {
+public abstract class AbstractTemplate<T> implements Template<T> {
 
     private final Class<? extends T> typeClass;
 

src/main/java/org/ical4j/template/Template.java

@@ -0,0 +1,26 @@
+package org.ical4j.template;
+
+import java.lang.reflect.InvocationTargetException;
+import java.util.function.UnaryOperator;
+
+/**
+ * A template encapsulates rules for creating and modifying complex iCalendar and
+ * vCard objects.
+ *
+ * @param <T> the applicable object type
+ */
+public interface Template<T> extends UnaryOperator<T> {
+
+    /**
+     * Apply the template to a new object instance. The use of this method requires
+     * that the applicable object type contains a default noargs constructor that
+     * can be used to create a new object instance.
+     * @return a new object instance resulting from applying the template
+     * @throws NoSuchMethodException if a noargs constructor doesn't exist on the applicable object type
+     * @throws InvocationTargetException an error resulting from invoking the noargs constructor
+     * @throws InstantiationException an error resulting from invoking the noargs constructor
+     * @throws IllegalAccessException an error resulting from invoking the noargs constructor
+     */
+    T apply() throws NoSuchMethodException, InvocationTargetException, InstantiationException,
+            IllegalAccessException;
+}