Print list items with Java streams

Question

I can use something like:

 .forEach(System.out::print) 

...to print my list items but if I have another operation to do before printing I can't use it like:

mylist.replaceAll(s -> s.toUpperCase()).forEach(System.out::print) 

I'm getting an error:

void cannot be dereferenced

Answer 1

You have to decide. When you want to modify the list, you can’t combine the operations. You need two statements then.

myList.replaceAll(String::toUpperCase);// modifies the list myList.forEach(System.out::println); 

---

If you just want to map values before printing without modifying the list, you’ll have to use a Stream:

myList.stream().map(String::toUpperCase).forEachOrdered(System.out::println); 

Answer 2

If you want to print and save modified values simultaneously you can do

List<String> newValues = myList.stream().map(String::toUpperCase) .peek(System.out::println).collect(Collectors.toList());