Displaying the contents of an array of objects

Question

Hello All,
My Java teacher gave us a challenge and I'm stumped. The teacher wants us to display the contents of the array in the main menthod. The original code is as follows:
public class TestObjects
     public static void main ( String args[] )
          Thing[] thingArray = { new Thing(4), new Thing(7) };
}I understand that the elements of the array are objects, and each one has a value assigned to it. The following code was my first attempt at a solution:
public class TestObjects
     public static void main ( String args[] )
          Thing[] thingArray = { new Thing(4), new Thing(7) };
                                for ( int i = 0; i < thingArray.length; i++)
                                   System.out.println( thingArray );                         
}To which I'm given what amounts to garbage output. I learned from reading about that output that its basically displaying the memory location of the array, and the the contents of the array. There was mention of overriding or bypassing a method in System.out.println, but I don't believe that we're that far advanced yet. Any thoughts? I know I have to get at the data fields in the objects of the array, but i'm not having an easy time figuring it out. Thanks very much in advance!

Answer 1

robrom78 wrote:
public class TestObjects
     public static void main ( String args[] )
          Thing[] thingArray = { new Thing(4), new Thing(7) };
for ( int i = 0; i < thingArray.length; i++)
System.out.println( thingArray );                         
Note that you're trying to print the entire array at every loop iteration. That's probably not what you meant to do.
You probably meant to do something more like
                             System.out.println( thingArray[i] );Also, note that the java.util.Arrays class has a toString method that might be useful.
To which I'm given what amounts to garbage output. It's not garbage. It's the default output to toString() for arrays, which is in fact the toString() defined for java.lang.Object (and inherited by arrays).
I learned from reading about that output that its basically displaying the memory location of the array, and the the contents of the array.It displays a default result that is vaguely related to the memory, but probably shouldn't be thought of us such. Think of it as identifying the type of object, and a value that differentiates it from other objects of the same type.
By the way I assume you mean "+not+ the contents of the array" above. If so, that is correct.
There was mention of overriding or bypassing a method in System.out.println, but I don't believe that we're that far advanced yet. Any thoughts? No, you don't override a method in println; actually methods don't contain other methods directly. You probably do need to override toString in Thing.
I know I have to get at the data fields in the objects of the array, but i'm not having an easy time figuring it out. You can get to the individual objects in the array just by dereferencing it, as I showed you above.
But I suspect that won't be sufficient. Most likely, Thing doesn't have a toString method defined. This means that you'll end up with very similar output, but it will say "Thing" instead of "[Thing" and the numbers to the right of the "@" will be different.
You'll need to override the toString() method in Thing to get the output you want.