java在继承中使用super（）

Question

我在使用Inheritance构造类，并且在使用super()时遇到了困难。我有InterestCalculator class这是CompoundInterest Class的母公司。我想在复利class.Your构造使用super() InterestCalculator需要3 paramenters（本金，的InterestRate和长期） 我需要调用CompoundInterest这需要4 parameters，我需要通过3（ PrincipalAmount，InterestRate和Term）和4th parameter特定于CompoundInterest。

import java.util.Scanner; 
public class InterestCalculator 
{ 

    protected double principalAmount; 
    protected double interestRate; 
    protected int term; 

    public InterestCalculator(double principalAmount, double interestRate,   int term) 
    { 
    this.principalAmount = principalAmount; 
    this.interestRate= interestRate; 
    this.term = term; 
    } 
    public double getPrincipal() 
    { 
     return principalAmount; 
    }  
    public double getInterestRate() 
    { 
    return interestRate; 
    } 
    public double getTerm() 
    { 
    return term; 
    } 
    public double calcInterest() 
    { 
    return -1; 
    } 
    protected double convertTermToYears() 
    { 
    return (this.term/12.0); 
    } 
    protected double convertInterestRate() 
    { 
    return (this.interestRate/100.0); 
    } 
} 
public class CompoundInterest extends InterestCalculator 
{ 
    protected int compoundMultiplier = 0;  

    super.CompoundInterest(double compoundMultiplier); 
    { 
    super.principalAmount = principalAmount; 
    super.interestRate = interestRate; 
    super.term = term; 
    this.compoundMultiplier = (int) compoundMultiplier; 
    } 
    public double calcInterest() 
    { 
    double calcInterest = (super.principalAmount *Math.pow((1.0+((super.convertInterestRate())/this.compoundMultiplier)),(this.compoundMultiplier *(super.convertTermToYears()))))- super.principalAmount;    
    return calcInterest;  
    } 
} 

Answer 1

您需要定义在派生类的构造函数接受所有它要需要的参数：

public class CompoundInterest extends InterestCalculator { 
    protected int compoundMultiplier; 

    /** 
    * Constructor for CompoundInterest. 
    */ 
    public CompoundInterest(double principalAmount, double interestRate, int term, 
     int compoundMultiplier) 
    { 
     super(principalAmount, interestRate, term); 
     this.compoundMultiplier = compoundMultiplier; 
    } 

    . . . // rest of class 
} 

注意，在构造函数中，super(...)调用父类的构造。您不要通过将super.放在您的构造函数名称前面来执行此操作。 通过调用super(...)（如果存在，它必须是子类构造函数的第一行），将调用匹配的基类构造函数，并将使用参数来设置适当的字段。没有必要尝试从子类中再次尝试。

Answer 2

CompoundInterest类有几个错误。

1 - 您必须调用superclasst构造函数。由于InterestCalculator只有一个构造函数(double, double, int)，因此您需要在CompoundInterest构造函数的开始处对其进行调用。

2 - 您在super.CompoundInterest上以错误的方式使用super。 super用于访问超类中的方法。您必须将其重命名为CompoundInterest。

3 - 如第一项所述，您需要调用超类的构造函数。你这样做：super(principalAmount, interestRate);。记住：它必须是构造函数的第一个调用。

4 - 您未传递给CompountInterest它所期望的三个参数中的任何一个。您应该考虑将这些参数也放入CompoundInterest中。

如果您将这些改变，你的代码将魔神像这样：

CompoundInterest(double compoundMultiplier, double principalAmount, double interestRate, int term); { 
    super(principalAmount, interestRate, term); 
    this.compoundMultiplier = (int) compoundMultiplier; 
}