svn merge -c 1342514 from trunk. Backports HADOOP-8323 (harsh).

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1342516 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -24,6 +24,8 @@ Release 2.0.1-alpha - UNRELEASED
 
     HADOOP-8403. bump up POMs version to 2.0.1-SNAPSHOT. (tucu)
 
+    HADOOP-8323. Add javadoc and tests for Text.clear() behavior (harsh)
+
   BUG FIXES
 
     HADOOP-8372. NetUtils.normalizeHostName() incorrectly handles hostname

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/Text.java

@@ -236,6 +236,11 @@ public class Text extends BinaryComparable
 
   /**
    * Clear the string to empty.
+   *
+   * <em>Note</em>: For performance reasons, this call does not clear the
+   * underlying byte array that is retrievable via {@link #getBytes()}.
+   * In order to free the byte-array memory, call {@link #set(byte[])}
+   * with an empty byte array (For example, <code>new byte[0]</code>).
    */
   public void clear() {
     length = 0;

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/TestText.java

@@ -241,6 +241,30 @@ public class TestText extends TestCase {
     Text.validateUTF8(utf8, 0, length);
   }
 
+  public void testClear() throws Exception {
+    // Test lengths on an empty text object
+    Text text = new Text();
+    assertEquals(
+        "Actual string on an empty text object must be an empty string",
+        "", text.toString());
+    assertEquals("Underlying byte array length must be zero",
+        0, text.getBytes().length);
+    assertEquals("String's length must be zero",
+        0, text.getLength());
+
+    // Test if clear works as intended
+    text = new Text("abcd\u20acbdcd\u20ac");
+    int len = text.getLength();
+    text.clear();
+    assertEquals("String must be empty after clear()",
+        "", text.toString());
+    assertTrue(
+        "Length of the byte array must not decrease after clear()",
+        text.getBytes().length >= len);
+    assertEquals("Length of the string must be reset to 0 after clear()",
+        0, text.getLength());
+  }
+
   public void testTextText() throws CharacterCodingException {
     Text a=new Text("abc");
     Text b=new Text("a");