[CIShell-SVN] SF.net SVN: cishell:[1144] trunk/core/org.cishell.utilities/src/org/cishell /utilities/OrderingUtilities.java

[<jrb...@us...>]

Revision: 1144
          http://cishell.svn.sourceforge.net/cishell/?rev=1144&view=rev
Author:   jrbibers
Date:     2010-10-22 18:08:52 +0000 (Fri, 22 Oct 2010)

Log Message:
-----------
Adding utilities for the Google Guava extension of Comparator, Ordering.  We add decorators for Ordering.explicit() to handle ordering of unspecified values.

Added Paths:
-----------
    trunk/core/org.cishell.utilities/src/org/cishell/utilities/OrderingUtilities.java

Added: trunk/core/org.cishell.utilities/src/org/cishell/utilities/OrderingUtilities.java
===================================================================
--- trunk/core/org.cishell.utilities/src/org/cishell/utilities/OrderingUtilities.java	                        (rev 0)
+++ trunk/core/org.cishell.utilities/src/org/cishell/utilities/OrderingUtilities.java	2010-10-22 18:08:52 UTC (rev 1144)
@@ -0,0 +1,73 @@
+package org.cishell.utilities;
+
+import java.util.Collection;
+import java.util.List;
+
+import com.google.common.base.Function;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Ordering;
+
+public class OrderingUtilities {
+	/**
+	 * Normally Ordering.explicit() gives an Ordering that throws a ClassCastException for
+	 * unspecified values.  This method gives an explicit ordering that puts unspecified values
+	 * before all others.
+	 * <br/><br/>
+	 * Until {@link http://code.google.com/p/guava-libraries/issues/detail?id=332} is addressed.
+	 */
+	public static <T> Ordering<T> explicitWithUnknownsFirst(List<T> valuesInOrder) {
+		Function<T, T> unknownToNullFunction = new IdentityIndicatorFunction<T>(valuesInOrder);
+
+		return Ordering.explicit(valuesInOrder).nullsFirst().onResultOf(unknownToNullFunction);
+	}
+	
+	/**
+	 * {@link org.cishell.utilities.OrderingUtilities.explicitWithUnknownsFirst(List<T>)}
+	 */
+	public static <T> Ordering<T> explicitWithUnknownsFirst(
+			T leastValue, T... remainingValuesInOrder) {
+		return explicitWithUnknownsFirst(Lists.asList(leastValue, remainingValuesInOrder));
+	}
+	
+	
+	/**
+	 * Normally Ordering.explicit() gives an Ordering that throws a ClassCastException for
+	 * unspecified values.  This method gives an explicit ordering that puts unspecified values
+	 * after all others.
+	 * <br/><br/>
+	 * Until {@link http://code.google.com/p/guava-libraries/issues/detail?id=332} is addressed.
+	 */
+	public static <T> Ordering<T> explicitWithUnknownsLast(List<T> valuesInOrder) {
+		Function<T, T> unknownToNullFunction = new IdentityIndicatorFunction<T>(valuesInOrder);
+
+		return Ordering.explicit(valuesInOrder).nullsLast().onResultOf(unknownToNullFunction);
+	}
+	
+	/**
+	 * {@link org.cishell.utilities.OrderingUtilities.explicitWithUnknownsLast(List<T>)}
+	 */
+	public static <T> Ordering<T> explicitWithUnknownsLast(
+			T leastValue, T... remainingValuesInOrder) {
+		return explicitWithUnknownsLast(Lists.asList(leastValue, remainingValuesInOrder));
+	}
+	
+	/**
+	 * For values in the given collection, this is the identity function.
+	 * For other values we return null.
+	 */
+	public static class IdentityIndicatorFunction<T> implements Function<T, T> {
+		private Collection<? extends T> values;
+
+		public IdentityIndicatorFunction(Collection<? extends T> values) {
+			this.values = values;
+		}
+		
+		public T apply(T candidateValue) {
+			if (values.contains(candidateValue)) {
+				return candidateValue;
+			} else {
+				return null;
+			}
+		}
+	}
+}


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