cheking on symmetric number

Question

How check number on symmetrics?

public static int Symmetric(int a) {
    if(new StringBuilder(Integer.toString(a)) ==
        new StringBuilder(Integer.toString(a)).reverse())
        return  a;
    else
        return 0;
}

I try do it smth like this but always return 0.

The idea is good, but the problem is the comparison. Using `==` you're comparing the instance values of the `StringBuilder`s, you should use `equals` to compare them. — Luiggi Mendoza, Feb 23 '13 at 22:26
@SevaAlekseyev looks like it, that's why I haven't posted an answer. — Luiggi Mendoza, Feb 23 '13 at 22:27

Keppil · Accepted Answer · 2013-02-23T22:38:40.770

4

You can't use == to compare Strings (or StringBuilders), you need to use equals().
Also, you need to turn the StringBuilders back to Strings before comparing:

EDIT: Also, there is really no need for the first StringBuilder:

public static int symmetric(int a) {
    if (Integer.toString(a).equals(new StringBuilder(Integer.toString(a)).reverse().toString()))
        return a;
    else
        return 0;
}

edited Feb 23 '13 at 22:38

answered Feb 23 '13 at 22:26

Keppil

45,603
8
97
119

thank for answer) But i again get 0 :( System.out.println(isSymmetric(101)); return 0... – Roman Chyzh Feb 23 '13 at 22:31
@RomanChyzh: This method yields `121` for `121` and `0` for `1231` when I test it. – Keppil Feb 23 '13 at 22:32
emm... sorry) awherything is well) i don't convert to string this : (Integer.toString(a)) – Roman Chyzh Feb 23 '13 at 22:36

score 0 · Answer 2 · answered Feb 23 '13 at 22:28

Equality is explained here in JLS.

You must use equals() on Strings: StringBuilder.toString().equals().

public static int Symmetric( int a ) {
    return
       new StringBuilder(Integer.toString(a)).toString().equals(
             StringBuilder(Integer.toString(a)).reverse().toString())
       ? a : 0;
}

cheking on symmetric number

2 Answers2