GNU Smalltalk-继承和多参数方法/构造函数

Question

假设我正在尝试将以下Java类转换为GNU Smalltalk：

public abstract class Account {

    protected String number;
    protected Customer customer;
    protected double balance;

    public abstract void accrue(double rate);

    public double balance() {
        return balance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public void withdraw(double amount) {
        balance -= amount;
    }

    public String toString() {
        return number + ":" + customer + ":" + balance;
    }
}

public class SavingsAccount extends Account {

    private double interest = 0;

    public SavingsAccount(String number, Customer customer, double balance) {
        this.number = number;
        this.customer = customer;
        this.balance = balance;
    }

    public void accrue(double rate) {
        balance += balance * rate;
        interest += interest * rate;
    }

}

我正在努力了解如何编写带有多个参数的方法/构造函数。到目前为止，这是我得到的：

Object subclass: Account [

    |number customer balance|

    balance [
        ^balance
    ]

    deposit: amount [
         balance := balance + amount
    ]

    withdraw: amount [
        balance := balance - amount
    ]

    asString [
        ^number asString, ':', customer asString, ':', balance asString
    ]

]

Account subclass: SavingsAccount [

    |interest|

    SavingsAccount class [
        new [ "add some sort of support for multiple arguments?"
           "call init"
        ]
    ]

    init [ "add some sort of support for multiple arguments?"
         interest := 0.
         balance := accountBalance.
         customer := accountCustomer.
         number := accountNumber
    ]

    accrue: rate [
        balance := balance + (balance * rate).
        interest := interest + (interest * rate)
    ]

]

几个问题：

1. 如何使Account成为Smalltalk中的抽象类？
2. 我假设所有的Account实例变量都可以通过SavingsAccount类中的名称进行访问吗？
3. 如何实现类似于Java SavingsAccount类中的多参数构造函数的东西？

Answer 1

1. 您不应该为某种“使类抽象化”而烦恼：）。但是最接近您问题的解决方案是

   abstractMethod [
   self subclassResponsibility
   

   ]

现在，当有人向您的类发送消息时，他会得到一个错误，指出应该实现此方法，并且您必须在子类中重写它。

1. 是。子类可以访问所有实例变量。

2. 好的，因此关键字消息之类的withdraw: amount实际上可以具有多个参数，例如：withdraw: amount becauseOf: reason。因此，首先要进行初始化：

   initWithBalance: aBalance customer: aCustomer number: aNumber [ 
   self init.
   balance := aBalance.
   customer := aCustomer.
   number := aNumber
   

   ]

您可以保持interest := 0.main init。然后，为了使您的生活更好，您可以进行参数设置new并init从那里html" target="_blank">调用参数设置。

    SavingsAccount class [
    newWithBalance: aBalance customer: aCustomer number: aNumber [
       ^ self new initWithBalance: aBalance customer: aCustomer number: aNumber
    ]
]