BAEL-1525: Review comments incorporated. (#3639)

core-java/src/main/java/com/baeldung/string/Palindrome.java

@@ -5,58 +5,62 @@ import java.util.stream.IntStream;
 public class Palindrome {
 
     public boolean isPalindrome(String text) {
-        text = text.replaceAll("\\s+", "")
-            .toLowerCase();
-        int length = text.length();
+        String clean = text.replaceAll("\\s+", "").toLowerCase();
+        int length = clean.length();
         int forward = 0;
         int backward = length - 1;
-        boolean palindrome = true;
         while (backward > forward) {
-            char forwardChar = text.charAt(forward++);
-            char backwardChar = text.charAt(backward--);
+            char forwardChar = clean.charAt(forward++);
+            char backwardChar = clean.charAt(backward--);
             if (forwardChar != backwardChar)
                 return false;
         }
-        return palindrome;
+        return true;
     }
 
     public boolean isPalindromeReverseTheString(String text) {
-        String reverse = "";
-        text = text.replaceAll("\\s+", "").toLowerCase();
-        char[] plain = text.toCharArray();
+        StringBuilder reverse = new StringBuilder();
+        String clean = text.replaceAll("\\s+", "").toLowerCase();
+        char[] plain = clean.toCharArray();
         for (int i = plain.length - 1; i >= 0; i--)
-            reverse += plain[i];
-        return reverse.equals(text);
+            reverse.append(plain[i]);
+        return (reverse.toString()).equals(clean);
     }
 
     public boolean isPalindromeUsingStringBuilder(String text) {
-        StringBuilder plain = new StringBuilder(text);
+        String clean = text.replaceAll("\\s+", "").toLowerCase();
+        StringBuilder plain = new StringBuilder(clean);
         StringBuilder reverse = plain.reverse();
-        return reverse.equals(plain);
+        return (reverse.toString()).equals(clean);
     }
 
     public boolean isPalindromeUsingStringBuffer(String text) {
-        StringBuffer plain = new StringBuffer(text);
+        String clean = text.replaceAll("\\s+", "").toLowerCase();
+        StringBuffer plain = new StringBuffer(clean);
         StringBuffer reverse = plain.reverse();
-        return reverse.equals(plain);
+        return (reverse.toString()).equals(clean);
     }
 
-    public boolean isPalindromeRecursive(String text, int forward, int backward) {
+    public boolean isPalindromeRecursive(String text) {
+        String clean = text.replaceAll("\\s+", "").toLowerCase();
+        return recursivePalindrome(clean, 0, clean.length() - 1);
+    }
+
+    private boolean recursivePalindrome(String text, int forward, int backward) {
         if (forward == backward)
             return true;
         if ((text.charAt(forward)) != (text.charAt(backward)))
             return false;
         if (forward < backward + 1) {
-            return isPalindromeRecursive(text, forward + 1, backward - 1);
+            return recursivePalindrome(text, forward + 1, backward - 1);
         }
 
         return true;
     }
-    
+
     public boolean isPalindromeUsingIntStream(String text) {
-        String temp  = text.replaceAll("\\s+", "").toLowerCase();
+        String temp = text.replaceAll("\\s+", "").toLowerCase();
         return IntStream.range(0, temp.length() / 2)
             .noneMatch(i -> temp.charAt(i) != temp.charAt(temp.length() - i - 1));
     }
-    
 }