Objective-C Programming: The Big Nerd Ranch Guide

A basic init method

In some cases, an initial value of zero for your instance variables may work fine. In others, however, you will need instances of your class to come into the world with their instance variables initialized to non-zero values.

Let’s say that every instance of BNRAppliance should start its life with a voltage of 120. In BNRAppliance.m, override NSObject’s init method by adding a new implementation of init.

          - (instancetype)init
{
    // Call the NSObject's init method
    self = [super init];

    // Did it return something non-nil?
    if (self) {

        // Give voltage a starting value
        _voltage = 120;
    }

    // Return a pointer to the new object
    return self;
}

        

Now when you create a new instance of BNRAppliance, it will have a voltage of 120 ...