Missing return statement error in Java

Question

I am currently writing a palindrome tester in Java for a class I am taking in high school. I have asked my teacher for assistance and he is also confused as well. I was hoping the community on stackoverflow could help me out. Thank you.

public class Palindrome
{
    private String sentence;
    public Palindrome(String s)
    {
        sentence = s;
    }

    public boolean isPalindrome()
    {
        if(sentence.length() <= 1)
        {
            return true;
        }

        if(sentence.charAt(0) == sentence.charAt(sentence.length()-1))
        {
            sentence = sentence.substring(1, sentence.length()-1);
            isPalindrome();
        }
        else
            return false;
    }

}

Answer 1

You need return isPalindrome(); . Otherwise the method isn't returning anything in that case, and it's declared to return a boolean.

Answer 2

Change

if (sentence.charAt(0) == sentence.charAt(sentence.length()-1))
{
    sentence = sentence.substring(1, sentence.length()-1);
    isPalindrome();
}

to

if (sentence.charAt(0) == sentence.charAt(sentence.length()-1))
{
    sentence = sentence.substring(1, sentence.length()-1);
    return isPalindrome();
}

In order to have the method complied, JVM need to make sure the method has a return statement for every possible case (which is something you haven't done).

Answer 3

If your code takes this path there is no return statement. If your teacher is confused, you need a new teacher.

if(sentence.charAt(0) == sentence.charAt(sentence.length()-1))
{
    sentence = sentence.substring(1, sentence.length()-1);
    isPalindrome();
}

Answer 4

如果您真的想在else子句中返回false，则您的最后一个if子句会错过返回。

Answer 5

You want to use a recursive way to check if the sentence is palindrome. you'd better to return isPalindrome() method inside following snippet

if(sentence.charAt(0) == sentence.charAt(sentence.length()-1))
        {
            sentence = sentence.substring(1, sentence.length()-1);
            return isPalindrome();
        }

This is my code:

public class palindrome
{
    private String sentence;
    public palindrome(String s)
    {
        sentence = s;
    }

    public boolean isPalindrome()
    {
        if(sentence.length() <= 1)
        {
            return true;
        }

        if(sentence.charAt(0) == sentence.charAt(sentence.length()-1))
        {
            sentence = sentence.substring(1, sentence.length()-1);
            return isPalindrome();
        }
        else
            return false;
    }

    public static void main(String [] args)
    {
        palindrome p=new palindrome("aabbaa");
        if(p.isPalindrome())
            System.out.println("yes");
        else
            System.out.println("no");
    }
}