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Also, can the user buy and sell many times?

If so, I have an idea.

Preferably use an ArrayList, though you could use a Vector I suppose.

Have an ArrayList of products.

Say you start out...

Not sure if you're using console or JOptionPane, but

use a char

char c = 'c';
String str = "";

System.out.println("Enter a Y for yes or N for no");
str = console.nextLine();