How to compare two StringBuffer Objects using .equals() method? [duplicate]

Question

This question already has answers here:

Comparing StringBuffer content with equals (11 answers)

Closed 8 years ago.

The following code did not work. Can anyone tell me what's wrong with the following code. Logically it should work...

package assignments;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class IsPalindrome {
public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(
                                      new InputStreamReader(System.in));
    System.out.println("Enter a Word:");
    StringBuffer sb1 = new StringBuffer(br.readLine());
    StringBuffer sb2 = new StringBuffer(sb1);
    sb1.reverse();

    if(sb2.equals(sb1))
        System.out.println("Palindrome");
    else
        System.out.println("Not a Palindrome");
}
}

Answer 1

Try

sb1.toString().equals(sb2.toString());

because StringBuffer#toString method returns the String value of the data stored inside the buffer:

Returns a string representing the data in this sequence. A new String object is allocated and initialized to contain the character sequence currently represented by this object. This String is then returned. Subsequent changes to this sequence do not affect the contents of the String.

Answer 2

In StringBuffer class equals method is not overriden as in String class. In StringBuffer it just looks whether the references are the same. Therefore you first need to convert that to a String and then use equals method.

So Try

sb1.toString().equals(sb2.toString());

Answer 3

You can write

System.out.println("Enter a line:");
String line = br.readLine().replace(" ", ""); // palindromes can have spaces
String reverse = new StringBuilder(sb1).reverse().toString();

if(line.equals(reverse))
    System.out.print("Not a ");
System.out.println("Palindrome");