2 files changed, 73 insertions, 0 deletions
diff --git a/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java b/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java
index 311b32c7bf..3ee30bd4b5 100644
--- a/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java
+++ b/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java
@@ -16,6 +16,9 @@
 package com.vaadin.shared.util;
 
 import java.io.Serializable;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.Locale;
 
 /**
@@ -145,6 +148,9 @@ public class SharedUtil implements Serializable {
      * @return The constructed string of words and separators
      */
     public static String join(String[] parts, String separator) {
+        if (parts.length == 0) {
+            return "";
+        }
         StringBuilder sb = new StringBuilder();
         for (int i = 0; i < parts.length; i++) {
             sb.append(parts[i]);
@@ -266,4 +272,39 @@ public class SharedUtil implements Serializable {
         return join(parts, "");
     }
 
+    /**
+     * Checks if the given array contains duplicates (according to
+     * {@link Object#equals(Object)}.
+     * 
+     * @param values
+     *            the array to check for duplicates
+     * @return <code>true</code> if the array contains duplicates,
+     *         <code>false</code> otherwise
+     */
+    public static boolean containsDuplicates(Object[] values) {
+        int uniqueCount = new HashSet<Object>(Arrays.asList(values)).size();
+        return uniqueCount != values.length;
+    }
+
+    /**
+     * Return duplicate values in the given array in the format
+     * "duplicateValue1, duplicateValue2".
+     * 
+     * @param values
+     *            the values to check for duplicates
+     * @return a comma separated string of duplicates or an empty string if no
+     *         duplicates were found
+     */
+    public static String getDuplicates(Object[] values) {
+        HashSet<Object> set = new HashSet<Object>();
+        LinkedHashSet<String> duplicates = new LinkedHashSet<String>();
+        for (Object o : values) {
+            if (!set.add(o)) {
+                duplicates.add(String.valueOf(o));
+            }
+
+        }
+        return join(duplicates.toArray(new String[duplicates.size()]), ", ");
+    }
+
 }
diff --git a/shared/src/test/java/com/vaadin/shared/util/SharedUtilTest.java b/shared/src/test/java/com/vaadin/shared/util/SharedUtilTest.java
index 081f594a97..6d8cab4fea 100644
--- a/shared/src/test/java/com/vaadin/shared/util/SharedUtilTest.java
+++ b/shared/src/test/java/com/vaadin/shared/util/SharedUtilTest.java
@@ -118,4 +118,36 @@ public class SharedUtilTest {
         }
     }
 
+    @Test
+    public void duplicatesInArray() {
+        Assert.assertTrue(
+                SharedUtil.containsDuplicates(new Object[] { "a", "a" }));
+        Assert.assertTrue(
+                SharedUtil.containsDuplicates(new Object[] { "a", "b", "a" }));
+        Assert.assertTrue(SharedUtil
+                .containsDuplicates(new Object[] { "a", "b", "a", "b" }));
+        Assert.assertTrue(
+                SharedUtil.containsDuplicates(new Object[] { 1, "b", 1 }));
+
+        Assert.assertFalse(SharedUtil.containsDuplicates(new Object[] {}));
+        Assert.assertFalse(SharedUtil.containsDuplicates(new Object[] { "a" }));
+        Assert.assertFalse(
+                SharedUtil.containsDuplicates(new Object[] { "a", "b" }));
+        Assert.assertFalse(
+                SharedUtil.containsDuplicates(new Object[] { "1", 1 }));
+    }
+
+    @Test
+    public void getDuplicates() {
+        Assert.assertEquals("", SharedUtil.getDuplicates(new Object[] { "a" }));
+        Assert.assertEquals("a",
+                SharedUtil.getDuplicates(new Object[] { "a", "a" }));
+        Assert.assertEquals("a, b",
+                SharedUtil.getDuplicates(new Object[] { "a", "b", "a", "b" }));
+        Assert.assertEquals("a, b, c", SharedUtil
+                .getDuplicates(new Object[] { "c", "a", "b", "a", "b", "c" }));
+        Assert.assertEquals("1.2",
+                SharedUtil.getDuplicates(new Object[] { 1.2, "a", 1.2 }));
+    }
+
 }