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

Question

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"); } }

You may want to use StringBuilder instead of StringBuffer (if you don't access it from multiple threads), as it's faster. — Gabriel Negut
– Gabriel Negut, Commented Jun 14, 2013 at 14:19
This might answer your query stackoverflow.com/questions/2012305/… — Gaurav Goyal
– Gaurav Goyal, Commented Jun 14, 2013 at 14:22
StringBuffer doesn't override equals() inherited from Object so contents in the StringBuffer aint compared just their reference. — Sello
– Sello, Commented Jun 14, 2013 at 14:29
If you don't already know, you should read the API documentation rather than making assumptions about the behavior of methods. The StringBuffer documentation says its equals method is inherited from Object. — Patricia Shanahan
– Patricia Shanahan, Commented Jun 14, 2013 at 14:31
Please don't use StringBuffer if you can use StringBuilder. This class has been deprecated for almost 10 years now. vanillajava.blogspot.com/2012/08/… — Peter Lawrey
– Peter Lawrey, Commented Jun 14, 2013 at 14:47

darijan · Accepted Answer · 2013-06-14 14:18:49Z

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.

Thanks @darijan it worked but why can't we compare two stringbuffer objects directly?
Well, because equals method is not implemented in such way for StringBuffers. It returns true only when a StringBuffer is comapred to itself.
@user1377586 StringBuffer doesn't have its own equals implementation so the call ends up in Object's implementation that is reference based.

Dulanga · Accepted Answer · 2013-06-14 14:30:01Z

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());

Peter Lawrey · Accepted Answer · 2013-06-14 14:50:04Z

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");

Collectives™ on Stack Overflow

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

3 Answers 3

3 Comments

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

Comments

Linked

Related