Write a program that reads a string from the console.

Write a program that reads a string from the console. If the string is empty or there is no input, it outputs Hello, world!. Otherwise it outputs Hello, followed by the contents of the string.

For example, with interleaved input of John:

Enter a string: John Hello, John!

Note the last line should be terminated by a newline.

Hint: Use hasNextLine() of the Scanner class to check if there is input.