From a4c5380ffe636edc0acbab144080adbc709d668c Mon Sep 17 00:00:00 2001
From: Kevin Cooney <kcooney@google.com>
Date: Mon, 30 May 2011 20:28:12 -0700
Subject: [PATCH] Optimize Filter.intersect() for common cases -
 ALL.intersect(filter) - filter.intersect(ALL) - filter.intersect(filter)

---
 .../org/junit/runner/manipulation/Filter.java     | 10 +++++++++-
 .../org/junit/tests/manipulation/FilterTest.java  | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/main/java/org/junit/runner/manipulation/Filter.java b/src/main/java/org/junit/runner/manipulation/Filter.java
index f5e0e09bd872..c0f31b0b40c4 100644
--- a/src/main/java/org/junit/runner/manipulation/Filter.java
+++ b/src/main/java/org/junit/runner/manipulation/Filter.java
@@ -30,7 +30,12 @@ public String describe() {
 		@Override
 		public void apply(Object child) throws NoTestsRemainException {
 			// do nothing
-		};
+		}
+
+		@Override
+		public Filter intersect(Filter second) {
+			return second;
+		}
 	};
 	
 	/**
@@ -89,6 +94,9 @@ public void apply(Object child) throws NoTestsRemainException {
 	 * by this Filter and {@code second}
 	 */
 	public Filter intersect(final Filter second) {
+		if (second == this || second == ALL) {
+			return this;
+		}
 		final Filter first= this;
 		return new Filter() {
 			@Override
diff --git a/src/test/java/org/junit/tests/manipulation/FilterTest.java b/src/test/java/org/junit/tests/manipulation/FilterTest.java
index 16c1ff0c8d1d..242e9907f242 100644
--- a/src/test/java/org/junit/tests/manipulation/FilterTest.java
+++ b/src/test/java/org/junit/tests/manipulation/FilterTest.java
@@ -1,6 +1,7 @@
 package org.junit.tests.manipulation;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 import org.junit.Test;
 import org.junit.runner.Description;
 import org.junit.runner.manipulation.Filter;
@@ -31,4 +32,18 @@ public void intersectionText() {
 		assertEquals("a and b", a.intersect(b).describe());
 		assertEquals("b and a", b.intersect(a).describe());
 	}
+	
+	@Test
+	public void intersectSelf() {
+		NamedFilter a= new NamedFilter("a");
+		assertSame(a, a.intersect(a));
+	}
+	
+	@Test
+	public void intersectAll() {
+		NamedFilter a= new NamedFilter("a");
+		assertSame(a, a.intersect(Filter.ALL));
+		assertSame(a, Filter.ALL.intersect(a));
+		assertSame(Filter.ALL, Filter.ALL.intersect(Filter.ALL));
+	}
 }