Why when String ... keyIn=null; does keyIn= key; generate error "cannot convert char to String"?

sfoerster

This code does what I want, but there are two odd things that I can not rationalize:

1) When keyIn is a String and null .. keyIn = key; generate an error message "cannot convert char to String" .. But keyIn = " " + key; works

2)Immediately trying to trim the lead space fails, but putting the trim command after the second character is entered works

I am writing because I want to use this in the future where I may try to input a string that starts with a space. And this will strip the space no matter what.

This code works and has the questions in the context of the code:

String keyIn = ""; 
void setup() {}
void draw() {}
void keyPressed() {
  if (key == RETURN || key == ENTER) {
      println(".."+keyIn);
      keyIn = null;
    } else {
      if (keyIn == null) {
           // keyIn = key; doesn't work .. generates message "cannot convert from char to String" ... why?
           keyIn = " " + key;
           // keyIn = trim(keyIn); doesn't work here .. but does work below ... why?
      } else {
           keyIn = keyIn + key;
           keyIn = trim(keyIn);//now this will clip any leading space someone tries to type in the future and look like a bug if this code is reused ... is there another solution?
      }
    }
}

GoToLoop

But keyIn = " " + key; works.

String + "anything" results another String in Java!

• String s = "" + key;
• String s = key + "";
• String s = str(key);

That is so b/c the + binary operator is overloaded for both addition & concatenation operations:
http://processing.org/reference/addition.html

Immediately trying to trim() the lead space fails,...

Function trim() accepts String or String[] parameters only:
http://processing.org/reference/trim_.html

Alternatively, we can use trim() method from String class:
http://docs.oracle.com/javase/8/docs/api/java/lang/String.html#trim--

_vk

edit: late : )

The + operator is doing the conversion for you, you can use Processing's str() to it by yourself:

String keyIn = ""; 
void setup() {}
void draw() {}
void keyPressed() {
  if (key == RETURN || key == ENTER) {
      println(".."+keyIn);
      keyIn = null;
    } else {
      if (keyIn == null) {
           // keyIn = key; doesn't work .. generates message "cannot convert from char to String" ... why?
           keyIn =str(key);
           // keyIn = trim(keyIn); doesn't work here .. but does work below ... why?
      } else {
           keyIn += str(key);
      }
    }
}