Author: tn
Date: Thu Aug 16 20:50:27 2012
New Revision: 1374049
URL: http://svn.apache.org/viewvc?rev=1374049&view=rev
Log:
[COLLECTIONS-393] Added ListUtils.partition method, thanks to Chris Shayan for
report and patch.
Modified:
commons/proper/collections/trunk/src/changes/changes.xml
commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/ListUtils.java
commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/TestListUtils.java
Modified: commons/proper/collections/trunk/src/changes/changes.xml
URL:
http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/changes/changes.xml?rev=1374049&r1=1374048&r2=1374049&view=diff
==============================================================================
--- commons/proper/collections/trunk/src/changes/changes.xml (original)
+++ commons/proper/collections/trunk/src/changes/changes.xml Thu Aug 16
20:50:27 2012
@@ -22,6 +22,9 @@
<body>
<release version="4.0" date="TBA" description="Next release">
+ <action issue="COLLECTIONS-393" dev="tn" type="add" due-to="Chris Shayan">
+ Added "ListUtils#partition" method to split a List into consecutive
sublists.
+ </action>
<action issue="COLLECTIONS-272" dev="tn" type="add" due-to="Chaitanya
Mutyala">
Added serialization support for "FixedOrderComparator" and
"TransformingComparator".
</action>
Modified:
commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/ListUtils.java
URL:
http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/ListUtils.java?rev=1374049&r1=1374048&r2=1374049&view=diff
==============================================================================
---
commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/ListUtils.java
(original)
+++
commons/proper/collections/trunk/src/main/java/org/apache/commons/collections/ListUtils.java
Thu Aug 16 20:50:27 2012
@@ -16,6 +16,7 @@
*/
package org.apache.commons.collections;
+import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
@@ -438,5 +439,73 @@ public class ListUtils {
}
return -1;
}
+
+ /**
+ * Returns consecutive {@link List#subList(int, int) sublists} of a
+ * list, each of the same size (the final list may be smaller). For
example,
+ * partitioning a list containing {@code [a, b, c, d, e]} with a partition
+ * size of 3 yields {@code [[a, b, c], [d, e]]} -- an outer list containing
+ * two inner lists of three and two elements, all in the original order.
+ * <p>
+ * The outer list is unmodifiable, but reflects the latest state of the
+ * source list. The inner lists are sublist views of the original list,
+ * produced on demand using {@link List#subList(int, int)}, and are subject
+ * to all the usual caveats about modification as explained in that API.
+ * <p>
+ * Adapted from http://code.google.com/p/guava-libraries/
+ *
+ * @param <T> the element type
+ * @param list the list to return consecutive sublists of
+ * @param size the desired size of each sublist (the last may be smaller)
+ * @return a list of consecutive sublists
+ * @throws IllegalArgumentException if list is {@code null} or size is not
strictly positive
+ */
+ public static <T> List<List<T>> partition(List<T> list, int size) {
+ if (list == null) {
+ throw new IllegalArgumentException("List must not be null");
+ }
+ if (size <= 0) {
+ throw new IllegalArgumentException("Size must be greater than 0");
+ }
+ return new Partition<T>(list, size);
+ }
+ /**
+ * Provides a partition view on a {@link List}.
+ */
+ private static class Partition<T> extends AbstractList<List<T>> {
+ private final List<T> list;
+ private final int size;
+
+ private Partition(List<T> list, int size) {
+ this.list = list;
+ this.size = size;
+ }
+
+ public List<T> get(int index) {
+ int listSize = size();
+ if (listSize < 0) {
+ throw new IllegalArgumentException("negative size: " +
listSize);
+ }
+ if (index < 0) {
+ throw new IndexOutOfBoundsException("Index " + index + " must
not be negative");
+ }
+ if (index >= listSize) {
+ throw new IndexOutOfBoundsException("Index " + index + " must
be less than size " +
+ listSize);
+ }
+ int start = index * size;
+ int end = Math.min(start + size, list.size());
+ return list.subList(start, end);
+ }
+
+ public int size() {
+ return (list.size() + size - 1) / size;
+ }
+
+ @Override
+ public boolean isEmpty() {
+ return list.isEmpty();
+ }
+ }
}
Modified:
commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/TestListUtils.java
URL:
http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/TestListUtils.java?rev=1374049&r1=1374048&r2=1374049&view=diff
==============================================================================
---
commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/TestListUtils.java
(original)
+++
commons/proper/collections/trunk/src/test/java/org/apache/commons/collections/TestListUtils.java
Thu Aug 16 20:50:27 2012
@@ -22,6 +22,7 @@ import java.util.Collection;
import java.util.Collections;
import java.util.List;
+import junit.framework.Assert;
import junit.framework.Test;
import org.apache.commons.collections.functors.EqualPredicate;
@@ -30,12 +31,7 @@ import org.apache.commons.collections.li
/**
* Tests for ListUtils.
*
- * @version $Revision$
- *
- * @author Stephen Colebourne
- * @author Neil O'Toole
- * @author Matthew Hawthorne
- * @author Dave Meikle
+ * @version $Id$
*/
public class TestListUtils extends BulkTest {
@@ -297,4 +293,32 @@ public class TestListUtils extends BulkT
assertEquals(ListUtils.indexOf(fullList, null), -1);
}
+ public void testPartition() {
+ List<Integer> strings = new ArrayList<Integer>();
+ for (int i = 0; i <= 6; i++) {
+ strings.add(i);
+ }
+
+ final List<List<Integer>> partition = ListUtils.partition(strings, 3);
+
+ assertNotNull(partition);
+ assertEquals(3, partition.size());
+ assertEquals(1, partition.get(2).size());
+
+ try {
+ ListUtils.partition(null, 3);
+ Assert.fail("failed to check for null argument");
+ } catch (IllegalArgumentException e) {}
+
+ try {
+ ListUtils.partition(strings, 0);
+ Assert.fail("failed to check for size argument");
+ } catch (IllegalArgumentException e) {}
+
+ try {
+ ListUtils.partition(strings, -10);
+ Assert.fail("failed to check for size argument");
+ } catch (IllegalArgumentException e) {}
+
+ }
}
