摘要 class 值未在“扩展”中注册 class

Question

我写了 Java 代码，使用抽象来计算联邦和 state 从工资中计算所得税。

代码如下。

import java.util.Scanner;

abstract class USA_Tax{
    protected final double income_tax = 0.15;
    protected double pre_tax_amount;
    protected double tax_to_fed;

    public void federal_tax(){
        Scanner input = new Scanner (System.in);
        System.out.println ("Enter pre-tax income: ");
        double pre_tax_amount = input.nextDouble();
        System.out.println ("Money owned to federal government: ");
        tax_to_fed = (double)(pre_tax_amount*0.15);
        System.out.println (tax_to_fed);
    input.close();
    }
}

class California_Tax extends USA_Tax{
    protected final double ca_income_tax = 0.10;
    protected double after_california_tax;
    protected double total_money_left;
    public void ca_tax(){
        after_california_tax = (double)(pre_tax_amount * ca_income_tax);
        System.out.println("Money owned to CA government: " + after_california_tax);
        total_money_left = (pre_tax_amount) - (after_california_tax + tax_to_fed);
        System.out.println ("Total take home:" + total_money_left);
    }    
}

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

        California_Tax tax1 = new California_Tax();
        tax1.federal_tax();
        tax1.ca_tax();
    }
}

当我运行代码时，似乎只有来自抽象 class 的值才能正确弹出。 扩展 class 中的 after_california_tax 和 total_money_left 变量的值显示为 0.0。 下面是一个例子 output。

Enter pre-tax income: 
100000
Money owned to federal government: 
15000.0
Money owned to CA government: 0.0
Total take home:-15000.0

我还尝试从第一个 class 中删除“抽象”，但没有任何改变。

我究竟做错了什么？

Answer 1

在public void federal_tax()中，您重新定义变量pre_tax_amount ：

double pre_tax_amount = input.nextDouble();

因此，您没有使用上面定义的成员变量。 您需要在已声明的变量中分配值：

pre_tax_amount = input.nextDouble();

Answer 2

这是你搞砸的地方，你创建了一个不需要的新局部变量，使用你定义的实例变量代替。

double pre_tax_amount = input.nextDouble();

修改完成后的代码

    import java.util.Scanner;

abstract class USA_Tax{
    protected final double income_tax = 0.15;
    protected double pre_tax_amount;
    protected double tax_to_fed;

    public void federal_tax(){
        Scanner input = new Scanner (System.in);
        System.out.println ("Enter pre-tax income: ");
        pre_tax_amount = input.nextDouble();
        System.out.println ("Money owned to federal government: ");
        tax_to_fed = (double)(pre_tax_amount*0.15);
        System.out.println (tax_to_fed);
    input.close();
    }
}

class California_Tax extends USA_Tax{
    protected final double ca_income_tax = 0.10;
    protected double after_california_tax;
    protected double total_money_left;
    public void ca_tax(){
        after_california_tax = (double)(pre_tax_amount * ca_income_tax);
        System.out.println("Money owned to CA government: " + after_california_tax);
        total_money_left = (pre_tax_amount) - (after_california_tax + tax_to_fed);
        System.out.println ("Total take home:" + total_money_left);
    }    
}

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

        California_Tax tax1 = new California_Tax();
        tax1.federal_tax();
        tax1.ca_tax();
    }
}

Answer 3

虽然我认为其他答案可以解决您的具体问题。 感觉您对抽象 class 的用途没有真正的了解。 一般来说，抽象 class 是一个 class，它没有定义所有行为，并且该行为必须由决定使用该 class 的实施者/程序员定义。在您的示例中，如何计算不同的税率。

要使用实际抽象，我们需要一个具有实际抽象方法的父对象 class。

public abstract class Tax {

    private double income;

    public Tax(double income) {
        this.income = income;
    }
    public void printCalculation() {

        System.out.println("Money owned to federal government: ");
        double tax_to_fed = income * getTaxAmount();
        System.out.println(tax_to_fed);
    }

    public abstract double getTaxAmount();
}

然后我们有两个实现类。

public class UsaTax extends Tax {
    public UsaTax(double income) {
        super(income);
    }

    @Override
    public double getTaxAmount() {
        return .15;
    }
}

public class CaliforniaTax extends Tax {

    public CaliforniaTax(double income) {
        super(income);
    }

    @Override
    public double getTaxAmount() {
        return .10;
    }
}

最后我们有我们的主要 class。

import java.util.Scanner;

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

        Scanner input = new Scanner (System.in);
        System.out.println ("Enter pre-tax income: ");
        double pre_tax_amount = input.nextDouble();
        UsaTax usaTax = new UsaTax(pre_tax_amount);
        usaTax.printCalculation();
        CaliforniaTax californiaTax = new CaliforniaTax(pre_tax_amount);
        californiaTax.printCalculation();

        // We could even create an anonymous inner class
        Tax texasTax = new Tax(pre_tax_amount) {
            @Override
            public double getTaxAmount() {
                return 0;
            }
        };
        texasTax.printCalculation();
        input.close();
    }
}

output：

Enter pre-tax income: 
10000
Money owned to federal government: 
1500.0
Money owned to federal government: 
1000.0
Money owned to federal government: 
0.0

Process finished with exit code 0

边注

我相信您首先尝试创建抽象类的原因是在父 class 中使用扫描仪。通过将扫描仪行为从您的 Tax class 中分离出来，我们减少了该类与用户输入方法的耦合，并允许我们编写class 只考虑它的行为，而不是它需要做什么以及如何正确处理用户输入。