Lets say I have a method which returns a list with a random number of random numbers - we will call that method List<Integer> getRandomNumberOfRandomNumbers();
System.out.println(String.format("Here are the random numbers: %s", getRandomNumberOfRandomNumbers()));
I know this won't work but how can I achieve this effect?
Here are the random numbers:
1 4 2 4
Here are the random numbers:
2 43 323 434 3423 54
It's easiest to just make getRandomNumberOfRandomNumbers return all of the numbers in a single String. Or you could do it all inline, like this:
getRandomNumberOfRandomNumbers().stream()
.map(Object::toString)
.collect(Collectors.joining(" "));
For example, if we have a List of Integers as below:
List<Integer> var = new ArrayList<>();
var.add(1);
var.add(4);
var.add(2);
var.add(4);
Then to print the List in your desired way, you can follow this:
System.out.println(String.format("Here are the random numbers:%n%n%s",
var.toString().replaceAll("[,\\[,\\]]", "")));
This outputs:
Here are the random numbers:
1 4 2 4
Here var is the list your function getRandomNumberOfRandomNumbers() is returning and we are converting it to String using var.toString() but it returns [1, 4, 2, 4]. So, we need to remove [, ] and ,. I used regular expression to replace them with an empty character. This is actually simple and easy way but not sure whether it is an efficient way!! Whenever i need to convert a Colletion to String, i use toString() method and then do some trick with regular expression to get my desired form of representation.
Update: After surfing web, i found few alternatives. (Preferred over my previous answer using List.toString())
For example, in your case, you can do:
StringJoiner sj = new StringJoiner(" ");
for (Integer i : var) {
sj.add(String.valueOf(i));
}
System.out.println(sj.toString());
You can do the same with the following two alternatives.
%n not \n
%n over \n? and when you said List's toString() can be changed, did you mean if java API changes? i guess the probability is pretty low and yes off course, we can change our code if someday toString() returns different string representation.
%n is OS independant.Another solution is iterating through the list and adding the values to a string builder before printing it out
like so:
StringBuilder stringBuilder = new StringBuilder();
for(Integer number : getRandomNumberOfRandomNumbers())
stringBuilder.append(number + " ");
System.out.println("Here are the random numbers: " + stringBuilder.toString().trim());
