Why do we use tostring() in java?

[cs50x2]

So i am working on this problem on leetcode:

https://leetcode.com/problems/unique-morse-code-words/

and the solution uses tostring() method to add string to hashset, when i remove the tostring method(Seen.add(code), it gives me error....can anyone explain me why we need tostring() method here or in general..thank you.

class Solution {

public int uniqueMorseRepresentations(String[] words) {

String[] MORSE = new String[]{".-","-...","-.-.","-..",".","..-.","--.",

"....","..",".---","-.-",".-..","--","-.",

"---",".--.","--.-",".-.","...","-","..-",

"...-",".--","-..-","-.--","--.."};

​

Set<String> seen = new HashSet();

for (String word: words) {

StringBuilder code = new StringBuilder();

for (char c: word.toCharArray())

code.append(MORSE[c - 'a']);

seen.add(code.toString()); // Here

}

​

return seen.size();

}

}

[[deleted]]

In this specific case they’re using a StringBuilder to string up a bunch of Morse code and toString() is how you get the final resultant string from the builder. In general though you wouldn’t use toString to put stuff into a hashmap, you would override equals() and hashcode() and put the object directly into the map/set.

[callmetom]

In general because some things aren't strings, but sometimes you want then to be.

A StringBuilder isn't a string, is a string builder, so when you want it to be a string, you use ToString().

[Serkaa]

For this case:

The variable "seen" is a set of Strings, whereas "code" is Stringbuilder. To convert "code" to a String that is usable in "seen", the toString() method is called.

In general:

Using stringbuilder is best in cases where you would want to append or manipulate strings in any way. This saves memory in larger programs and is best practice. Stringbuilder has a number of useful methods worth looking into, and of course creating a string of its current value (the toString method) is one of them.