Java Streams — Python List/Dict Comprehension But In Java

If you clicked on this article, I’m guessing that you might be a Python main who needs to work with Java for whatever reason — be it for work or an existing project etc.

A Simple Sample Problem

Let’s say we have a list containing 3 string values:

The list in Python

list1 = ["apple", "orange", "pear"]

The ArrayList in Java

List<String> list1 = new ArrayList<>();
list1.add("apple");
list1.add("orange");
list1.add("pear");

Let’s say that we want to create another list containing the uppercase versions of the fruits inside ["APPLE", "ORANGE", "PEAR"]

In Python, this is how we might get this new list:

list2 = []
for fruit in list1:
    list2.append(fruit.upper())
print(list2) # ["APPLE", "ORANGE", "PEAR"]

This would be the equivalent in Java:

List<String> list2 = new ArrayList<>();
for (String fruit: list1) {
    list2.add(fruit.toUpperCase());
}
System.out.println(list2);

If you think this method is long and unelegant, here’s a shorter way to do it: