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采用多个参数的方法/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?
- 我假设在 SavingsAccount 类中只能通过名称访问所有 Account 实例变量是否正确?
- 如何在 Java SavingsAccount 类中实现模仿多参数构造函数的东西?
最佳答案
你不应该为某种“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,他会收到一个错误,指出应该实现此方法,您必须在子类中重写它。
是的。子类可以访问所有实例变量。
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,比如:withdraw: amount becauseOf: reason
。所以首先你做一个初始化程序:initWithBalance: aBalance customer: aCustomer number: aNumber [ self init. balance := aBalance. customer := aCustomer. number := aNumber ]
您可以在主
init
中保持interest := 0.
。 然后,为了让您的生活更美好,您创建一个参数化的new
并从那里调用参数化的init
。SavingsAccount class [ newWithBalance: aBalance customer: aCustomer number: aNumber [ ^ self new initWithBalance: aBalance customer: aCustomer number: aNumber ] ]
关于java - GNU Smalltalk - 继承和多参数方法/构造函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19205533/