Bug 1299201 - StringUtils: Add helper method for joining strings with a separator. r=Grisha

MozReview-Commit-ID: Fzrap4wkeWk

--HG--
extra : rebase_source : c0d6495d825ad0a8a80d05a39e38d841d758e115

mobile/android/geckoview/src/main/java/org/mozilla/gecko/util/StringUtils.java

@@ -13,6 +13,7 @@ import org.mozilla.gecko.AppConstants.Versions;
 
 import java.util.Collections;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Set;
 
 public class StringUtils {
@@ -271,4 +272,23 @@ public class StringUtils {
 
         return "\u200E" + text;
     }
+
+    /**
+     * Joining together a sequence of strings with a separator.
+     */
+    public static String join(@NonNull String separator, @NonNull List<String> parts) {
+        if (parts.size() == 0) {
+            return "";
+        }
+
+        final StringBuilder builder = new StringBuilder();
+        builder.append(parts.get(0));
+
+        for (int i = 1; i < parts.size(); i++) {
+            builder.append(separator);
+            builder.append(parts.get(i));
+        }
+
+        return builder.toString();
+    }
 }

mobile/android/tests/background/junit4/src/org/mozilla/gecko/util/TestStringUtils.java

@@ -9,6 +9,9 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mozilla.gecko.background.testhelpers.TestRunner;
 
+import java.util.Arrays;
+import java.util.Collections;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -84,4 +87,21 @@ public class TestStringUtils {
         final String forcedAgainLtrString = StringUtils.forceLTR(forcedLtrString);
         assertEquals(5, forcedAgainLtrString.length());
     }
+
+    @Test
+    public void testJoin() {
+        assertEquals("", StringUtils.join("", Collections.<String>emptyList()));
+        assertEquals("", StringUtils.join("-", Collections.<String>emptyList()));
+        assertEquals("", StringUtils.join("", Collections.singletonList("")));
+        assertEquals("", StringUtils.join(".", Collections.singletonList("")));
+
+        assertEquals("192.168.0.1", StringUtils.join(".", Arrays.asList("192", "168", "0", "1")));
+        assertEquals("www.mozilla.org", StringUtils.join(".", Arrays.asList("www", "mozilla", "org")));
+
+        assertEquals("hello", StringUtils.join("", Collections.singletonList("hello")));
+        assertEquals("helloworld", StringUtils.join("", Arrays.asList("hello", "world")));
+        assertEquals("hello world", StringUtils.join(" ", Arrays.asList("hello", "world")));
+
+        assertEquals("m::o::z::i::l::l::a", StringUtils.join("::", Arrays.asList("m", "o", "z", "i", "l", "l", "a")));
+    }
 }