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：
- 如何使 Account 成为 Smalltalk 中的抽象类？
- 我假设所有 Account 实例变量只能通过 SavingsAccount 类中的名称访问是否正确？
- 如何实现模仿 Java SavingsAccount 类中的多参数构造函数的东西？
-
您不应该为某种“使类抽象”而烦恼:)。但最接近你的问题的解决方案是
abstractMethod [
self subclassResponsibility
]
现在，当有人向您的类发送消息时，他会收到一条错误消息，指出应该实现此方法，并且您必须在子类中重写它。
是的。所有实例变量都可以由子类访问。
-
好的，所以关键字消息就像withdraw: amount实际上可以有多个参数，例如：withdraw: amount becauseOf: reason。所以首先你要创建一个初始化程序：
initWithBalance: aBalance customer: aCustomer number: aNumber [
self init.
balance := aBalance.
customer := aCustomer.
number := aNumber
]
你可以保留interest := 0.在主要init。
然后，为了让你的生活更美好，你做了一个参数化的new并调用参数化init从那里。
SavingsAccount class [
newWithBalance: aBalance customer: aCustomer number: aNumber [
^ self new initWithBalance: aBalance customer: aCustomer number: aNumber
]
]
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