What does the following statement sequence print if the user input is 123? public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.print("Enter a number: "); String str = in.next(); str += 456; System.out.println(str); }

The program takes user input as a string and then concatenates another string to it. When the user enters "123", that value is initially stored in the variable str. The next line of code appends "456" to the current value of str using the += operator.

In Java, when you use the += operator with strings, it does not perform arithmetic addition; instead, it concatenates the strings. Therefore, when str which holds "123" is concatenated with "456", the result becomes "123456".

Finally, the program prints this concatenated result. Since "123" is correctly combined with "456" to form the string "123456", this is what gets printed to the console. The understanding of string concatenation in Java is key to reaching this conclusion.