See, the main() function is not required to be called explicitely, keep that function in a class and save the java file with the same name as the class in which main() is defined. So main() starting point in java.
Secondly in java String, Integer, Boolean Character all are classes defined. You should go through the java APIs that is java doc which is available whenever you install java on your machine. For any class in Java have a habit to refer this java doc.
I hope this will help you.