Adjust InefficientEmptyStringCheck documentation

InefficientEmptyStringCheckRule.java and the corresponding section
both contain information which the other doesn't. The class Javadoc and
the description section in performance.xml has thus been adjusted.

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/InefficientEmptyStringCheckRule.java

@@ -10,20 +10,22 @@ import net.sourceforge.pmd.lang.java.rule.AbstractInefficientZeroCheck;
 import net.sourceforge.pmd.lang.java.symboltable.JavaNameOccurrence;
 
 /**
- * This rule finds code which inefficiently determines empty strings. This code
+ * This rule finds code which inefficiently determines empty strings.
  *
+ * <p>
  * <pre>
  * str.trim().length()==0
  * </pre>
- *
- * <p>
- * is quite inefficient as trim() causes a new String to be created. Smarter
- * code to check for an empty string would be:
- * </p>
+ * or
+ * <pre>
+ * str.trim().isEmpty()
+ * </pre>
+ * (for the same reason) is quite inefficient as trim() causes a new String to
+ * be created. A Smarter code to check for an empty string would be:
  *
  * <pre>
  * private boolean checkTrimEmpty(String str) {
- *     for(int i=0; i<str.length(); i++) {
+ *     for(int i = 0; i < str.length(); i++) {
  *         if(!Character.isWhitespace(str.charAt(i))) {
  *             return false;
  *         }
@@ -31,7 +33,11 @@ import net.sourceforge.pmd.lang.java.symboltable.JavaNameOccurrence;
  *     return true;
  * }
  * </pre>
- * or Apache commons-lang's <code>StringUtils.isBlank</code>.
+ * or you can refer to Apache's <code>StringUtils#isBlank</code>
+ * (in commons-lang), Spring's <code>StringUtils#hasText</code> (in the Spring
+ * framework) or Google's <code>CharMatcher#whitespace</code> (in Guava) for
+ * existing implementations (some might include the check for != null).
+ * </p>
  *
  * @author acaplan
  */

pmd-java/src/main/resources/category/java/performance.xml

@@ -366,18 +366,34 @@ buf.append("1m");           // good
           class="net.sourceforge.pmd.lang.java.rule.performance.InefficientEmptyStringCheckRule"
           externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_performance.html#inefficientemptystringcheck">
         <description>
-String.trim().length() is an inefficient way to check if a String is really empty, as it
+<![CDATA[
+String.trim().length() == 0 (or String.trim().isEmpty() for the same reason) is an
+inefficient way to check if a String is really empty, as it
 creates a new String object just to check its size. Consider creating a static function that
 loops through a string, checking Character.isWhitespace() on each character and returning
-false if a non-whitespace character is found. You can refer to Apache's StringUtils#isBlank (in commons-lang),
-Spring's StringUtils#hasText (in the Spring framework) or Google's CharMatcher#whitespace (in Guava) for
-existing implementations.
+false if a non-whitespace character is found. A Smarter code to check for an empty string
+would be:
+
+private boolean checkTrimEmpty(String str) {
+    for(int i = 0; i < str.length(); i++) {
+        if(!Character.isWhitespace(str.charAt(i))) {
+            return false;
+        }
+    }
+    return true;
+}
+
+You can refer to Apache's StringUtils#isBlank (in commons-lang),
+Spring's StringUtils#hasText (in the Spring framework) or Google's
+CharMatcher#whitespace (in Guava) for existing implementations (some might
+include the check for != null).
+]]>
         </description>
         <priority>3</priority>
         <example>
 <![CDATA[
 public void bar(String string) {
-    if (string != null && string.trim().size() > 0) {
+    if (string != null && string.trim().length() > 0) {
         doSomething();
     }
 }