How to concat string values in array list

Question

I need to print all arraylist values at a time using concat.

Here is my code:

ArrayList lst = new ArrayList();
lst.add(\"hi\"         


        

Answer 1

The error in your code is pretty small. In each iteration you assign a value to the result variable. However instead of updating your existing content you just erase it and enter a new value.

You do result = element + " ". But it should be something like result = result + element + " " or the same in short:

result += element + " ";

This way the first iteration will save hi in it and after that hello gets appended resulting in hi hello (instead of overriding the content of the first iteration).

Note that it now also has the whitespace at the end. You could delete it with result = result.substring(0, result.length() - 1). Or not add it in the last iteration, but then you need to count the iterations.

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Please note that Java has a class StringJoiner that does exactly what you want, joining some elements together and also using a delimiter like whitespace. You use it like this:

StringJoiner sj = new StringJoiner(" ");
while(itr.hasNext()) {
    Object element = itr.next();
    sj.add(element);
}
String result = sj.toString();

Also note that since Java 8 there is an even shorter version of it:

String result = String.join(" ", list);

Answer 2

Please prefer the List interface to the ArrayList concrete type. Assuming you are using Java 8+, you might use a Stream and Collectors.joining (and Arrays.asList) like

List<String> lst = Arrays.asList("hi", "hello");
String r = lst.stream().collect(Collectors.joining(" "));
System.out.println(r);

Which outputs

hi hello

As requested.