Use isEmpty().

Prefix internal class name with Abstract.
Fix Checkstyle XML.

Author: garydgregory

checkstyle-suppressions.xml

@@ -18,7 +18,7 @@ limitations under the License.
 -->
 
 <!DOCTYPE suppressions PUBLIC
-    -//Checkstyle//DTD SuppressionFilter Configuration 1.0//EN
+    "-//Checkstyle//DTD SuppressionFilter Configuration 1.0//EN"
     "https://checkstyle.org/dtds/suppressions_1_0.dtd">
 
 <suppressions>

src/main/java/org/apache/commons/codec/language/Caverphone1.java

@@ -43,7 +43,7 @@ public class Caverphone1 extends AbstractCaverphone {
     @Override
     public String encode(final String source) {
         String txt = source;
-        if (txt == null || txt.length() == 0) {
+        if (txt == null || txt.isEmpty()) {
             return SIX_1;
         }
 

src/main/java/org/apache/commons/codec/language/Caverphone2.java

@@ -43,7 +43,7 @@ public class Caverphone2 extends AbstractCaverphone {
     @Override
     public String encode(final String source) {
         String txt = source;
-        if (txt == null || txt.length() == 0) {
+        if (txt == null || txt.isEmpty()) {
             return TEN_1;
         }
 

src/main/java/org/apache/commons/codec/language/ColognePhonetic.java

@@ -199,7 +199,7 @@ public class ColognePhonetic implements StringEncoder {
      * However, it is not shared between threads, as it is constructed on demand
      * by the method {@link ColognePhonetic#colognePhonetic(String)}
      */
-    private abstract class CologneBuffer {
+    abstract class CologneBuffer {
 
         protected final char[] data;
 
@@ -225,6 +225,10 @@ public int length() {
         public String toString() {
             return new String(copyData(0, length));
         }
+
+        public boolean isEmpty() {
+            return length() == 0;
+        }
     }
 
     private class CologneOutputBuffer extends CologneBuffer {
@@ -353,7 +357,7 @@ public String colognePhonetic(final String text) {
             } else if (chr == 'S' || chr == 'Z') {
                 output.put('8');
             } else if (chr == 'C') {
-                if (output.length() == 0) {
+                if (output.isEmpty()) {
                     if (arrayContains(AHKLOQRUX, nextChar)) {
                         output.put('4');
                     } else {

src/main/java/org/apache/commons/codec/language/DaitchMokotoffSoundex.java

@@ -270,7 +270,7 @@ private static void parseRules(final Scanner scanner, final String location,
                 // trim leading-trailing whitespace
                 line = line.trim();
 
-                if (line.length() == 0) {
+                if (line.isEmpty()) {
                     continue; // empty lines can be safely skipped
                 }
 

src/main/java/org/apache/commons/codec/language/DoubleMetaphone.java

@@ -888,7 +888,7 @@ private String cleanInput(String input) {
             return null;
         }
         input = input.trim();
-        if (input.length() == 0) {
+        if (input.isEmpty()) {
             return null;
         }
         return input.toUpperCase(java.util.Locale.ENGLISH);

src/main/java/org/apache/commons/codec/language/Nysiis.java

@@ -253,7 +253,7 @@ public String nysiis(String str) {
         // Use the same clean rules as Soundex
         str = SoundexUtils.clean(str);
 
-        if (str.length() == 0) {
+        if (str.isEmpty()) {
             return str;
         }
 

src/main/java/org/apache/commons/codec/language/RefinedSoundex.java

@@ -189,7 +189,7 @@ public String soundex(String str) {
             return null;
         }
         str = SoundexUtils.clean(str);
-        if (str.length() == 0) {
+        if (str.isEmpty()) {
             return str;
         }
 

src/main/java/org/apache/commons/codec/language/Soundex.java

@@ -304,7 +304,7 @@ public String soundex(String str) {
             return null;
         }
         str = SoundexUtils.clean(str);
-        if (str.length() == 0) {
+        if (str.isEmpty()) {
             return str;
         }
         final char out[] = {'0', '0', '0', '0'};

src/main/java/org/apache/commons/codec/language/SoundexUtils.java

@@ -38,7 +38,7 @@ final class SoundexUtils {
      * @return A clean String.
      */
     static String clean(final String str) {
-        if (str == null || str.length() == 0) {
+        if (str == null || str.isEmpty()) {
             return str;
         }
         final int len = str.length();