// Zorah Fung, CSE 143
// A demo of "null"
public class NullDemo {
    public static void main(String[] args) {
        Student student = new Student();
        System.out.println(student.id);
        System.out.println(student.name);
        System.out.println(student.grades);
        // System.out.println(student.name.toLowerCase()); // throws NullPointerException
        // System.out.println(student.grades.add(42)); // throws NullPointerException

        Student student2 = null;
        /*
         * All of the following with throw NullPointerException
         * System.out.println(student2.id); System.out.println(student2.name);
         * System.out.println(student2.name.toLowerCase());
         */

        String word = "hello";
        String word2 = null;
        printNotNull("hello");
        printNotNull("");
        printNotNull("null");
        printNotNull(word);
        printNotNull(word2); // throws IllegalArgument exception
        printNotNull(null); // throws IllegalArgument exception
    }

    // Prints the given string, as long as it is not null.
    // If the given string is null, an IllegalArgumentException is thrown.
    public static void printNotNull(String s) {
        if (s == null) {
            throw new IllegalArgumentException("String parameter may not be null");
        }
        System.out.println(s);
    }
}