MyClass

import java.util.*;

public class MyClass {
    public static void main(String args[]) {
        List<String> myList = Arrays.asList("a1", "a2", "b1", "c2", "c1");
        myList.stream().map(x ->
        {
            if (x.startsWith("a")) {
                x = x.toUpperCase();
            }
            return x;
        }).forEach(System.out::println);
    }
}