In class on Friday we talked about nested if statements and ambiguous else statements. In particular, we looked at the code:

    if ( hr < 9 )
    if ( randNum == 0 )
    System.out.println("Good morning!");
    else
    System.out.println("Hi!");

This is actually legal (if unreadable) code, even without braces, because in Java an if/else statement, or even an if/else if/else if/else statement, is considered a single, complex statement.

The other important thing to know about Java in order to understand the code above is that when there is an ambiguous else, as in this example (is it the else for the first if or the second if?), it always associates with the most recent if.

This means that the code above is equivalent to

    if ( hr < 9 )
    {
        if ( randNum == 0 )
            System.out.println("Good morning!");
        else
            System.out.println("Hi!");
    }

In other words, if it is before 9 o'clock and if the random number is 0, then the code will print "Good morning!" If it is before 9 o'clock but the random number is something other than 0, it will print "Hi!" If the hour is 9 or later, nothing will be printed.

As someone mentioned in class, it is also equivalent to:

    if ( hr < 9 && randNum == 0 )
    {
        System.out.println("Good morning!");
    }
    else if ( hr < 9 )
    {
        System.out.println("Hi!");
    }

We then asked how we could change the code if we wanted to print "Good morning!" when the time is before 9 o'clock (but only if the random number is 0), and print "Hi!" when the time is 9 or later. In this case we would print nothing when the time is before 9 but the random number is not 0. Three valid ways of doing this were proposed.

    // Alternative 1
    if ( hr < 9 && randNum == 0 )
        System.out.println("Good morning!");
    else if ( randNum != 0 )
        System.out.println("Hi!");

    // Alternative 2
    if ( hr < 9 )
        if ( randNum == 0 )
            System.out.println("Good morning!");
        else
            ;
    else
        System.out.println("Hi!");

    // Alternative 3 (the one I showed on the screen)
    if ( hr < 9 )
    {
        if ( randNum == 0 )
            System.out.println("Good morning!");
    }
    else
        System.out.println("Hi!");