WEBVTT

1
00:00:00.220 --> 00:00:03.005
In this demo I'm going to create and inspect

2
00:00:03.006 --> 00:00:05.100
an instance of the BonusItem class.

3
00:00:05.223 --> 00:00:08.114
BonusItem is a subclass of the Item class

4
00:00:08.115 --> 00:00:10.113
that was previously in the project

5
00:00:11.227 --> 00:00:13.226
so lets create an instance

6
00:00:14.009 --> 00:00:18.117
BonusItem has two constructor parameters, description

7
00:00:19.220 --> 00:00:21.227
and codeWord

8
00:00:22.004 --> 00:00:24.118
so I'll just put in values for those

9
00:00:25.001 --> 00:00:28.009
and the instance is created in the object bench.

10
00:00:30.003 --> 00:00:31.224
So lets inspect the object

11
00:00:31.229 --> 00:00:34.111
before I do so, lets just have a quick look at the

12
00:00:34.111 --> 00:00:36.118
code inside the BonusItem class

13
00:00:36.220 --> 00:00:40.227
and notice it declares only one field codeWord

14
00:00:41.228 --> 00:00:44.226
so now I inspect the object

15
00:00:45.001 --> 00:00:47.224
and you can see the BonusItem object has two fields

16
00:00:47.225 --> 00:00:50.008
description and codeWord.

17
00:00:50.117 --> 00:00:53.007
only one of these was declared inside

18
00:00:53.112 --> 00:00:55.224
the BonusItem class itself.

19
00:00:56.009 --> 00:00:59.006
Note that a BonusItem object combines fields

20
00:00:59.007 --> 00:01:01.223
that are declared in two different classes

21
00:01:02.111 --> 00:01:05.002
but the object itself is a single object.

22
00:01:09.222 --> 00:01:11.221
Let's look at the methods that we can call

23
00:01:11.222 --> 00:01:15.008
on this BonusItem object, if I right click on the object

24
00:01:15.115 --> 00:01:17.223
you can see the bonus method

25
00:01:17.224 --> 00:01:19.222
thats the only method that is defined 

26
00:01:19.223 --> 00:01:21.113
in the BonusItem class

27
00:01:22.001 --> 00:01:25.004
I can call that and it produces some output

28
00:01:27.225 --> 00:01:30.119
but a BonusItem is a special type of item

29
00:01:30.220 --> 00:01:32.220
so it also should be able to do anything

30
00:01:32.222 --> 00:01:34.117
that an Item object can do

31
00:01:35.007 --> 00:01:38.004
and BlueJ lets us get at the methods

32
00:01:38.112 --> 00:01:40.113
that it inherits from an item

33
00:01:40.118 --> 00:01:43.004
with this menu option here then we can see

34
00:01:43.112 --> 00:01:46.116
all the methods that are part of the Item class.

35
00:01:46.229 --> 00:01:49.113
There is the use method that is defined an item

36
00:01:49.114 --> 00:01:52.221
I can call that on this BonusItem object

37
00:01:53.009 --> 00:01:56.111
and I get the output from that method.

38
00:01:59.004 --> 00:02:00.228
Note that all classes in Java

39
00:02:00.229 --> 00:02:03.118
are subclasses of a base class called Object

40
00:02:03.224 --> 00:02:06.115
so BonusItem is a subclass of Item

41
00:02:06.223 --> 00:02:09.112
which in turn is a subclass of Object.

42
00:02:10.114 --> 00:02:12.226
From the BonusItem object I can call

43
00:02:12.227 --> 00:02:16.113
the methods that are defined in the BonusItem class itself

44
00:02:16.228 --> 00:02:19.225
methods that are defined in the Item class

45
00:02:20.110 --> 00:02:23.117
and methods that are defined in the Object class.

46
00:02:24.005 --> 00:02:25.220
I'm not going to worry too much about what

47
00:02:25.221 --> 00:02:28.009
the Object class methods do for the moment though.