无法获取getter的值

q8l4jmvw 于 2021-07-06 发布在 Java

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我是新来编码的。我有三节课 Payment , CashPayment ，和 MainClass . 我想访问getter的payment类的值 CashPayment 方法。我打电话来了 Payment 进入 MainClass 设置 amountOfPayment 示例，然后通过中的getter访问它 CashPayment . 但是，它总是返回0。
付款.java

public class Payment {
    public double amountOfPayment;

    public Payment(){}

    public double getAmountOfPayment() {
        return this.amountOfPayment;
    }

    public void setAmountOfPayment(double amountOfPayment) {
        this.amountOfPayment = amountOfPayment;
    }
}

现金支付.java

public class CashPayment {

    public String paymentDetails() {
        Payment payment = new Payment();
        return "Payment : " + payment.getAmountOfPayment();
    }

}

付款驱动程序.java

public class PaymentDriver {
    public static void main(String args[]){

        Payment payment = new Payment();
        payment.setAmountOfPayment(200);
        CashPayment cashPayment = new CashPayment();
        System.out.println(cashPayment.paymentDetails());
}
}

输出 Payment : 0.0 //这应该是200.0

Java

来源：https://stackoverflow.com/questions/64832263/unable-to-fetch-value-of-getter

2条答案

按热度按时间

6yoyoihd1#

你用的是完全不同的 Payment 对象中的对象示例 paymentDetails() 方法，而不是您尝试引用的方法。
有很多方法可以解决这个问题。一个简单的，但不一定是建筑优雅的方式将是定义您的 paymentDetails() 采取措施 Payment 参数并传入在中创建的参数 main() ```
public class CashPayment {

public String paymentDetails(Payment payment) {
return "Payment : " + payment.getAmountOfPayment();
}

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vptzau2j2#

还有其他方法可以实现：
继承
如果 CashPayment 扩展 Payment 类，然后是它的方法 paymentDetails 不需要创建另一个 Payment 对象：

public class CashPayment extends Payment {
    public String paymentDetails() {
        return "Payment : " + this.getAmountOfPayment();
    }
}

那么驱动程序/测试方法如下所示：

Payment payment = new CashPayment();
payment.setAmountOfPayment(200);
CashPayment cashPayment = (CashPayment) payment; // casting needed
System.out.println(cashPayment.paymentDetails());

输出：

Payment : 200.0

聚合（示例） CashPayment 有一个示例 Payment ):
一 Payment 需要将带有setter的字段添加到 CashPayment 班级。或者，可以通过构造函数设置此字段。

public class CashPayment {
    private Payment payment;

    public void setPayment(Payment payment) {
        this.payment = payment;
    }

    public String paymentDetails() {
        if (null != payment) {
            return "Payment : " + payment.getAmountOfPayment();
        }
        return "No payment set";
    }
}

驱动程序类更新：

Payment payment = new Payment();
payment.setAmountOfPayment(200);
CashPayment cashPayment = new CashPayment();

System.out.println("before setting: " + cashPayment.paymentDetails());
cashPayment.setPayment(payment);
System.out.println("after setting: " + cashPayment.paymentDetails());

输出：

before setting: No payment set
after setting: Payment : 200.0

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无法获取getter的值

2条答案

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