testing array equality

[Amy Lee]

OK, I'm about to go crazy! I wrote a class that compares ClockTime - I set the class up using arrays. I want to compare two ClockTime objects and test for equality. My instance variable looks like:

private int[] myTime = new int[3];

My default constructor looks like:

public ClockTime()
myTime[0] = 0;
myTime[1] = 0;
myTime[2] = 0;

And my second constructor looks like:

public ClockTime(int hours, int minutes, int seconds)
myTime[0] = hours;
myTime[1] = minutes;
myTime[2] = seconds;

Say a user creates 2 ClockTime objects using either constructor, it doesn't matter which one. After the user creates these two objects, my equals() method needs to compare the two objects for equality - in other words, are they the same time or not.

I don't know if I'm having a brain fart or what, but I CAN'T FIGURE OUT HOW I'M SUPPOSED TO DO THIS. My assignment is due at 8:00 p.m. CST - will someone please help?!?!?!

THANKS!

[Layne Lund]

How about a for loop that checks if each coresponding element is equal?

Layne

[Amy Lee]

That sounds great, but two issues (for me at least):

1. How do I specify what I'm checking? When the user creates these two objects, they can name them anything they want. They can name the objects c1 and c2, or clock1 and clock2...etc. So how does my method know what objects to check?

2. My TA mentioned using the equals() method; i.e. c1.equals(c2) I've tried this method and it's not working.

[Mike Gershman]

You have to override equals(Object x) with your own version. Your two arrays are referenced through this and x. You need to check that the types are correct with instanceof and check that this.length == x.length.

Finally, loop over the array elements, checking equality.
[ November 06, 2004: Message edited by: Mike Gershman ]

[Layne Lund]

Originally posted by Amy Lee:
That sounds great, but two issues (for me at least):

1. How do I specify what I'm checking? When the user creates these two objects, they can name them anything they want. They can name the objects c1 and c2, or clock1 and clock2...etc. So how does my method know what objects to check?

2. My TA mentioned using the equals() method; i.e. c1.equals(c2) I've tried this method and it's not working.

As Mike says above, you need to create your own equals() method. When you call c1.equals(c2), the objects being compared are given "aliases" so to speak. Inside the equals() method, c1 can be referred to with the keyword "this" (without the quotes) and c2 can be referred to with the name of the parameter (i.e. x in Mike's example above). If this isn't clear, you probably need to review how methods work in general. This "aliasing" works no matter which method you call. It isn't specific to the equals() method described here.

HTH

Layne