Question

So, I was always a novice programmer but recently decided to learn Java. I was just messing around with a small constructor that was to take in a string and then write it backwards (my method of doing this was in no way supposed to be efficient, I was simply using different tools available to me in order to become accustomed.) My error came when I was trying to add a char in an array to a string. This is the code:

public class dids {

    char letters[];

    public dids(String thing)
    {
        letters= new char[thing.length()];  
        for(char x:letters){
            letters[x] = thing.charAt(x);
        }
        for(int i=thing.length();i>0;i--){
            String retval += letters[i];
        }
    }
}

The error is saying I cannot add a char to a string. A type mismatch.

Answer 1

public class dids { //classes start with an upper case letter (Dids not dids)

char letters[];

public dids(String thing)
{

letters= new char[thing.length()];  //No null check can throw NPE
for(char x:letters){ //letters is an empty array.  
    letters[x] = thing.charAt(x);  
}
for(int i=thing.length();i>0;i--){//style is to count up
    String retval += letters[i]; //retval is recreated every time

}

}

}   

you want to use String.toCharArray to populate your array like so:

letters = thing.toCharArray();

The below code reverse a String.

StringBuilder sb = new StringBuilder(thing);  
sb = sb.reverse();  
String retval = sb.toString();