如何设置 class 中的值 Present Value 以调用方法

Question

我目前正在尝试从 FutureValue 方法中的 PresentValue 方法中提取 return 值进行计算。

我试图通过声明 pv1 并仅使用该值来解决问题。新问题是它被设置为 0。

有谁知道我该如何解决这个问题，或者至少能够使用从现值 return 得到的值？

public class Bank1 {

    private double cash;
    private double rate = .0425;
    private int years;

    public Bank1(double cash, int years){
        this.cash = cash;
        this.years = years;     
    }

    private double pv1 = cash/Math.pow((1+rate), years);

    public double PresentValue(){
        double pv = cash/Math.pow((1+rate), years);
        double present = Math.round(pv *100);
        present = present/100;
        return present;
    }


    public double  FutureValue(){
        double fv = pv1*Math.pow((1+rate), years);
        double future = Math.round(fv *100);
        future = future/100;
        return future;
    }   

}

输出只是对方法的调用。

我收到的输出是

你想要多少钱？ 100

你投资了多少年？ 1

100.0 美元是您想要的金额。

95.92 美元是您需要投资的金额

$0.0 将是您的未来价值

感谢您的帮助！！

Answer 1

给FutureValue一个参数，这样你就可以传入结果：

public double FutureValue(double value) {
    //use value
}

调用时传入PresentValue的返回值：

double value = PresentValue();
double futureValue = FutureValue(value);

按照惯例，方法名称（标识符）应以小写字母开头。唯一应该以大写字母开头的是类型标识符（class/enum/interface 名称）或常量（静态最终变量）

Answer 2

只需更改 pv1*Math.pow((1+rate), years);

for this.PresentValue()*Math.pow((1+rate), years);

public class Bank1 {

private double cash;
private double rate = .0425;
private int years;

public Bank1(double cash, int years){
    this.cash = cash;
    this.years = years;     
}

private double pv1 = cash/Math.pow((1+rate), years);

public double PresentValue(){
    double pv = cash/Math.pow((1+rate), years);
    double present = Math.round(pv *100);
    present = present/100;
    return present;
}


public double  FutureValue(){
    double fv = this.PresentValue()*Math.pow((1+rate), years);
    double future = Math.round(fv *100);
    future = future/100;
    return future;
}   

public static void main(String args[]){
    Bank1 bank = new Bank1(100.0, 1);
    System.out.println("PresentValue: " + bank.PresentValue());
    System.out.println("FutureValue: " + bank.FutureValue());
}

}

Answer 3

有几种方法可以解决这个问题，但鉴于您的 class 是不可变的，最好的方法可能是在构造函数中预先计算当前值和未来值，然后简单地 return 它们来自访问器方法。请注意，我还将 presentValue 传递给 calculateFutureValue():

public class Bank1 {

    private double cash;
    private double rate = .0425;
    private int years;
    private double presentValue;
    private double futureValue;

    public Bank1(double cash, int years){
        this.cash = cash;
        this.years = years;
        presentValue = calculatePresentValue();
        futureValue = calculateFutureValue(presentValue);
    }

    private double calculatePresentValue(){
        double pv = cash/Math.pow((1+rate), years);
        double present = Math.round(pv *100);
        present = present/100;
        return present;
    }

    private double calculateFutureValue(final double value){
        double fv = value*Math.pow((1+rate), years);
        double future = Math.round(fv *100);
        future = future/100;
        return future;
    }  

    public double getPresentValue() {
        return presentValue;
    }

    public double getFutureValue() {
        return futureValue;
    } 

}

如何设置 class 中的值 Present Value 以调用方法

how can I set the value Present Value in my class to be called into a Method

java

eclipse

methods

class