Search:

What happened when you used an int value there instead a String?

Make the switch variable an int. All the case statements are int values. Get rid of the x variable.

Write a small program and try it to see what happens.

Look at what order the song lines are in as new lines are added:
1
then
2
1
then
3
2
1

Have you looked at the tutorial:
The switch Statement (The Java™ Tutorials > Learning the Java Language > Language Basics)