diff -N DecisionMakerPair.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ DecisionMakerPair.java	2 Jan 2006 21:16:14 -0000	1.1
@@ -0,0 +1,19 @@

+package org.lcsim.util.decision;
+
+import java.io.*;
+import java.util.*;
+
+/**
+  * A templated interface for a DecisionMaker that acts on a pair of objects.
+  *
+  * @version $Id: DecisionMakerPair.java,v 1.1 2006/01/02 21:16:14 mcharles Exp $
+  */
+public interface DecisionMakerPair<E,T> {
+
+  /**
+    * Check the pair of objects for validity.
+    * Return true if valid, false if not.
+    */
+    public boolean valid(E objectToTest1, T objectToTest2);
+
+}

diff -N DecisionMakerSingle.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ DecisionMakerSingle.java	2 Jan 2006 21:16:14 -0000	1.1
@@ -0,0 +1,16 @@

+package org.lcsim.util.decision;
+
+/**
+  * A templated interface for a DecisionMaker which takes a single
+  * object as input.
+  *
+  * @version $Id: DecisionMakerSingle.java,v 1.1 2006/01/02 21:16:14 mcharles Exp $   
+  */
+public interface DecisionMakerSingle<E> {
+
+  /**
+    * Return true if the object is valid, false if not.
+    */
+    public boolean valid(E objectToTest);
+
+}

diff -N DummyDecisionMakerPair.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ DummyDecisionMakerPair.java	2 Jan 2006 21:16:14 -0000	1.1
@@ -0,0 +1,12 @@

+package org.lcsim.util.decision;
+
+/**
+ * A dummy decision maker which always returns valid.
+ *
+ * @version $Id: DummyDecisionMakerPair.java,v 1.1 2006/01/02 21:16:14 mcharles Exp $
+ */
+
+public class DummyDecisionMakerPair<E,T> implements DecisionMakerPair<E,T> {
+    public DummyDecisionMakerPair () {}
+    public boolean valid(E objectToTest1, T objectToTest2) { return true; }
+}

diff -N DummyDecisionMakerSingle.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ DummyDecisionMakerSingle.java	2 Jan 2006 21:16:14 -0000	1.1
@@ -0,0 +1,12 @@

+package org.lcsim.util.decision;
+
+/**
+ * A dummy decision maker which always returns valid.
+ *
+ * @version $Id: DummyDecisionMakerSingle.java,v 1.1 2006/01/02 21:16:14 mcharles Exp $
+ */
+
+public class DummyDecisionMakerSingle<E> implements DecisionMakerSingle<E> {
+    public DummyDecisionMakerSingle () {}
+    public boolean valid(E objectToTest) { return true; }
+}

diff -N ExactMatchDecision.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ExactMatchDecision.java	2 Jan 2006 21:16:14 -0000	1.1
@@ -0,0 +1,27 @@

+package org.lcsim.util.decision;
+
+/**
+ * A decision maker that requires an exact match.
+ *
+ * @version $Id: ExactMatchDecision.java,v 1.1 2006/01/02 21:16:14 mcharles Exp $
+ */
+
+public class ExactMatchDecision<T> implements DecisionMakerSingle<T> {
+    /**
+     * Constructor.
+     *
+     * @param toBeMatched The value required for a valid match
+     */
+    public ExactMatchDecision(T toBeMatched) {
+	m_toBeMatched = toBeMatched;
+    }
+
+    /**
+     * Check whether test == toBeMatched
+     */
+    public boolean valid(T test) {
+	return (m_toBeMatched == test);
+    }
+
+    protected T m_toBeMatched;
+}

diff -N ListFilter.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ListFilter.java	2 Jan 2006 21:16:14 -0000	1.1
@@ -0,0 +1,49 @@

+package org.lcsim.util.decision;
+
+import java.util.*;
+
+/**
+  * A templated filter which applies a DecisionMakerSingle to each element in a list.
+  *
+  * @version $Id: ListFilter.java,v 1.1 2006/01/02 21:16:14 mcharles Exp $
+  */
+public class ListFilter<E> 
+{
+  /**
+    * Constructor.
+    *
+    * @param dec The DecisionMaker which will be applied.
+    */
+    public ListFilter (DecisionMakerSingle<E> dec) {
+      m_dec = dec;
+    }
+
+  /**
+    * Apply the filter to a list. The input list is unmodified;
+    * all elements that pass the filter are added to an output list
+    * which is supplied as the second parameter. The output is
+    * not wiped before the filtered elements of the input list are added.
+    *
+    * @param inputList  The input list (remains unmodified)
+    * @param outputList The output list (also the return value)
+    */
+    public List<E> filterList(List<E> inputList, List<E> outputList) {
+      for (E item : inputList) {
+        if (m_dec.valid(item)) {
+          outputList.add(item);
+        }
+      }
+      return outputList;
+    }
+
+  /**
+    * Apply the filter to a list. Returns a new List containing the
+    * filtered elements; the input list is not modified.
+    */
+    public List<E> filterList(List<E> inputList) {
+      List<E> emptyList = new ArrayList<E>();
+      return filterList(inputList, emptyList);
+    }
+
+    protected DecisionMakerSingle<E> m_dec = null;
+}