diff --git a/jdk/src/share/classes/java/lang/AbstractStringBuilder.java b/jdk/src/share/classes/java/lang/AbstractStringBuilder.java
index b87ebd73d9a..fc513f55efe 100644
--- a/jdk/src/share/classes/java/lang/AbstractStringBuilder.java
+++ b/jdk/src/share/classes/java/lang/AbstractStringBuilder.java
@@ -177,11 +177,10 @@ abstract class AbstractStringBuilder implements Appendable, CharSequence {
         ensureCapacityInternal(newLength);
 
         if (count < newLength) {
-            for (; count < newLength; count++)
-                value[count] = '\0';
-        } else {
-            count = newLength;
+            Arrays.fill(value, count, newLength, '\0');
         }
+
+        count = newLength;
     }
 
     /**
@@ -1308,8 +1307,7 @@ abstract class AbstractStringBuilder implements Appendable, CharSequence {
      *            {@code null}.
      */
     public int indexOf(String str, int fromIndex) {
-        return String.indexOf(value, 0, count,
-                              str.toCharArray(), 0, str.length(), fromIndex);
+        return String.indexOf(value, 0, count, str, fromIndex);
     }
 
     /**
@@ -1352,8 +1350,7 @@ abstract class AbstractStringBuilder implements Appendable, CharSequence {
      *          {@code null}.
      */
     public int lastIndexOf(String str, int fromIndex) {
-        return String.lastIndexOf(value, 0, count,
-                              str.toCharArray(), 0, str.length(), fromIndex);
+        return String.lastIndexOf(value, 0, count, str, fromIndex);
     }
 
     /**
diff --git a/jdk/src/share/classes/java/lang/String.java b/jdk/src/share/classes/java/lang/String.java
index f9550874c9e..d73a2f7c2e9 100644
--- a/jdk/src/share/classes/java/lang/String.java
+++ b/jdk/src/share/classes/java/lang/String.java
@@ -1705,6 +1705,24 @@ public final class String
                 str.value, 0, str.value.length, fromIndex);
     }
 
+    /**
+     * Code shared by String and AbstractStringBuilder to do searches. The
+     * source is the character array being searched, and the target
+     * is the string being searched for.
+     *
+     * @param   source       the characters being searched.
+     * @param   sourceOffset offset of the source string.
+     * @param   sourceCount  count of the source string.
+     * @param   target       the characters being searched for.
+     * @param   fromIndex    the index to begin searching from.
+     */
+    static int indexOf(char[] source, int sourceOffset, int sourceCount,
+            String target, int fromIndex) {
+        return indexOf(source, sourceOffset, sourceCount,
+                       target.value, 0, target.value.length,
+                       fromIndex);
+    }
+
     /**
      * Code shared by String and StringBuffer to do searches. The
      * source is the character array being searched, and the target
@@ -1796,6 +1814,24 @@ public final class String
                 str.value, 0, str.value.length, fromIndex);
     }
 
+    /**
+     * Code shared by String and AbstractStringBuilder to do searches. The
+     * source is the character array being searched, and the target
+     * is the string being searched for.
+     *
+     * @param   source       the characters being searched.
+     * @param   sourceOffset offset of the source string.
+     * @param   sourceCount  count of the source string.
+     * @param   target       the characters being searched for.
+     * @param   fromIndex    the index to begin searching from.
+     */
+    static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
+            String target, int fromIndex) {
+        return lastIndexOf(source, sourceOffset, sourceCount,
+                       target.value, 0, target.value.length,
+                       fromIndex);
+    }
+
     /**
      * Code shared by String and StringBuffer to do searches. The
      * source is the character array being searched, and the target