Using Java 8 to convert a list of objects into a string obtained from the toString() method

Question

There are a lot of useful new things in Java 8. E.g., I can iterate with a stream over a list of objects and then sum the values from a specific field of the Object

Answer 1

Just in case anyone is trying to do this without java 8, there is a pretty good trick. List.toString() already returns a collection that looks like this:

[1,2,3]

Depending on your specific requirements, this can be post-processed to whatever you want as long as your list items don't contain [] or , .

For instance:

list.toString().replace("[","").replace("]","") 

or if your data might contain square brackets this:

String s=list.toString();
s = s.substring(1,s.length()-1) 

will get you a pretty reasonable output.

One array item on each line can be created like this:

list.toString().replace("[","").replace("]","").replaceAll(",","\r\n")

I used this technique to make html tooltips from a list in a small app, with something like:

list.toString().replace("[","").replace("]","").replaceAll(",","
")

If you have an array then start with Arrays.asList(list).toString() instead

I'll totally own the fact that this is not optimal, but it's not as inefficient as you might think and is pretty straightforward to read and understand. It is, however, quite inflexible--in particular don't try to separate the elements with replaceAll if your data might contain commas and use the substring version if you have square brackets in your data, but for an array of numbers it's pretty much perfect.