Create a new project: a Foundation Command Line Tool called Appliances. In this program, you are going to create two classes: BNRAppliance and BNROwnedAppliance (a subclass of BNRAppliance). An instance of BNRAppliance will have a productName and a voltage. An instance of BNROwnedAppliance will also have a set containing the names of its owners.

Figure 33.1  BNRAppliance and its subclass, BNROwnedAppliance

Create a new file: an NSObject subclass named BNRAppliance. In BNRAppliance.h, create property declarations for productName and voltage:

#​i​m​p​o​r​t​ ​<​F​o​u​n​d​a​t​i​o​n​/​F​o​u​n​d​a​t​i​o​n​.​h​>​

@​i​n​t​e​r​f​a​c​e​ ​B​N​R​A​p​p​l​i​a​n​c​e​ ​:​ ​N​S​O​b​j​e​c​t​

@​p​r​o​p​e​r​t​y​ ​(​n​o​n​a​t​o​m​i​c​,​ ​c​o​p​y​)​ ​N​S​S​t​r​i​n​g​ ​*​p​r​o​d​u​c​t​N​a​m​e​;​
@​p​r​o​p​e​r​t​y​ ​(​n​o​n​a​t​o​m​i​c​)​ ​i​n​t​ ​v​o​l​t​a​g​e​;​

@​e​n​d​

You would create an instance of BNRAppliance like this:

B​N​R​A​p​p​l​i​a​n​c​e​ ​*​a​ ​=​ ​[​[​B​N​R​A​p​p​l​i​a​n​c​e​ ​a​l​l​o​c​]​ ​i​n​i​t​]​;​

Note that because BNRAppliance does not implement an init method, it will execute the init method defined in NSObject. When this happens, all the instance variables specific to BNRAppliance are zeroed out. Thus, the productName of a new instance of BNRAppliance will be nil, and voltage will be zero.