// Exercise 2
//
// every class in Java is also a type:
// you can define and use a variable whose type is a certain class
//   
// a very famous example is the class String, consider this:
//
//   String s = "chris";
//
// a Java programer would say "s is a variable that holds a reference
// to an object of class String" or more simply "s is a String object"
//
// you can use a lot of predefined classes from the standard library
// (such as String) or you can define your own
//
// type, compile and run this programm too and observe what you can
// do with objects!


public class DemoStrings {

    public static void main(String[] a) {
       
        // define a few String objects
        // and perform the + operation (concatenation) on them
 
        String str1 = "I'm a";
        String str2 = "student";

        String phrase = str1 + str2;
        String nice_phrase = str1 + " " + str2;

        System.out.println(phrase);
        System.out.println(nice_phrase);

        // contrary to built-in types, classes have methods
        // that you can call by using a dot . and round brackets ()
        
        System.out.println(nice_phrase.toUpperCase());    // method toUpperCase
        System.out.println(nice_phrase.substring(0, 3));  // method substring

        // can you figure out what these two methods do?


       // String is a class
       // note that the name String starts with an upper case letter,
       // as opposed to built-ins such as int and double
    }
}