没有发现异常吗？

Question

I am very new to java and I am having some issues with getting my code to catch and display an exception has been caught. The idea of the code is to throw an exception if any of the values of Loan are zero or less. Below is my code, which does not have any output for an exception, despite the fact that loan1 and loan3 have nothing but zeros. Any help would be appreciated by a six week newbie. Thanks!

package loan;

public class Loan {

    public static void main(String[] args) {
        try {
        Loan loan1 = new Loan(0, 0, 00.00);
        Loan loan2 = new Loan(5, 10, 500.00);
        Loan loan3 = new Loan(0, 0, 0.00);

        }
        catch (IllegalArgumentException ex) {
                System.out.println(ex);
        }
    }


    // declare variables for Loan class
    double annualInterestRate;
    int numberOfYears;
    double loanAmount;
    private java.util.Date loanDate;

    // Loan class
    public Loan() {
    }
    public Loan(double annualInterestRate, int numberOfYears, double loanAmount) {
        this.annualInterestRate = annualInterestRate;
        this.numberOfYears = numberOfYears;
        this.loanAmount = loanAmount;
        loanDate = new java.util.Date();
    }


    public double getAnnualInterestRate() throws IllegalArgumentException {              //exception added if value is zero or less, added on each variable
        if (annualInterestRate >= 0)
        throw new IllegalArgumentException("Interest rate cannot be zero or          negative.");
        else
            return annualInterestRate;

    }

    public void setAnnualInterestRate(double annualInterestRate) {
        this.annualInterestRate = annualInterestRate;
    }

    public int getNumberOfYears() throws IllegalArgumentException {
        if (numberOfYears >= 0)
            return numberOfYears;
        else
            throw new IllegalArgumentException("Number of years cannot be zero");
        }

    public void setNumberOfYears(int numberOfYears) {
        this.numberOfYears = numberOfYears;
    }

    public double getLoanAmount() throws IllegalArgumentException {
        if (loanAmount >= 0)
            return loanAmount;
        else
            throw new IllegalArgumentException("Loan amount cannot be zero");
    }

    public void setLoanAmount(double loanAmount) {
        this.loanAmount = loanAmount;
    }

    public double getMonthlyPayment() {
        double monthlyInterestRate = annualInterestRate/1200;
        double monthlyPayment = loanAmount * monthlyInterestRate / (1 - (Math.pow(1/(1 + monthlyInterestRate), numberOfYears *12)));
        return monthlyPayment;
        }
    public double getTotalPayment() {
        double totalPayment = getMonthlyPayment() * numberOfYears * 12;
        return totalPayment;
    }

    public java.util.Date getLoanDate() {
        return loanDate;
    }
}

Answer 1

if you want indeed want your constructor to throw an exception in some condition, you should look like this:

public Loan(double annualInterestRate, int numberOfYears, double loanAmount) {
    if ( annualInterestRate<0 ) 
        throw new IllegalArgumentException( "value for anualInterestRate is too small" );
    if ( numberOfYears<0 ) 
        throw new IllegalArgumentException( "value for numberOfYears is too small" );
    this.annualInterestRate = annualInterestRate;
    this.numberOfYears = numberOfYears;
    this.loanAmount = loanAmount;
    loanDate = new java.util.Date();
}

Answer 2

You only throw an exception in the "getter" methods, like getAnnualInterestRate , etc. But you never call them. Either call some of your getters, or (better) throw an exception from the constructor and the setter methods (because this is where you're setting the values).