Research of Stream API behavior in Java

This example shows a chain of Stream API calls. It is necessary to determine what output will appear in the console when the test() method is executed.

void test() {
    Stream.of("a", "b", "c")
        .map(letter -> {
            System.out.println(letter.toUpperCase()); 
            return letter.toUpperCase();
        })
        .map(letter -> {
            System.out.println(letter + 1); 
            return letter + 1;
        });
}