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;
    }

}

我很难理解如何编写带有多个参数的方法/构造函数。这是我到目前为止所得到的：

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：

如何在Smalltalk中将Account设为抽象类？
我是否正确假设所有帐户实例变量只能通过SavingsAccount类中的名称访问？
如何在Java SavingsAccount类中实现模仿多参数构造函数的东西？

Answer 1

你不应该打扰某种“制作类抽象”:)。但是最接近你问题的解决方案是
```
abstractMethod [
    self subclassResponsibility
]
```
现在，当有人向您的班级发送消息时，他会收到一个错误，即应该实施此方法，并且您必须在子类中覆盖它。
是。所有实例变量都可以由子类访问。

好的，所以像withdraw: amount这样的关键字消息实际上可以有多个参数，例如：withdraw: amount becauseOf: reason。首先，你要做一个初始化者：

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

您可以将interest := 0.保留在主init中。然后，为了让您的生活更美好，您可以进行参数化new并从那里调用参数化init。

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

GNU Smalltalk - 继承和多参数方法/构造函数

1 个答案: