Redefinition of methods
重新定义方法
In a subclass, we can change the behavior of the instances by redefining superclass methods.
在子类中，我们可以通过重定义继承自父类的方法来改变实例的行为。
ruby> class Human
| def identify
| puts "I'm a person."
| end
| def train_toll(age)
| if age < 12
| puts "Reduced fare.";
| else
| puts "Normal fare.";
| end
| end
| end
nil
ruby> Human.new.identify
I'm a person.
nil
ruby> class Student1<Human
| def identify
| puts "I'm a student."
| end
| end
nil
ruby> Student1.new.identify
I'm a student.
nil
Suppose we would rather enhance the superclass's identify method than entirely replace it. For this we can use super.
假如我们想要增强父类的的identify方法，而不是完全替换它。为此我们可以使用super。
ruby> class Student2<Human
| def identify
| super
| puts "I'm a student too."
| end
| end
nil
ruby> Student2.new.identify
I'm a person.
I'm a student too.
nil
super lets us pass arguments to the original method. It is sometimes said that there are two kinds of people...
super让我们将传递参数给原始的方法。有时会说，有两种人...
ruby> class Dishonest<Human
| def train_toll(age)
| super(11) # 我们想要便宜的车票
| end
| end
nil
ruby> Dishonest.new.train_toll(25)
Reduced fare.
nil
ruby> class Honest<Human
| def train_toll(age)
| super(age) # 传递我们给的参数
| end
| end
nil
ruby> Honest.new.train_toll(25)
Normal fare.
nil