未为类型Loan？定义方法Loan（double，int，double）。

Question

Can anyone help me see where I am missing this? I am trying to get the loan class called to the main method and check to see if my exception handling is right. I am very new to this, week six to be exact, and can use all the constructive help possible. Thanks ahead of time!

package loan;
import java.util.Scanner;

public class Loan {

public static void main(String[] args) {
    try {
        Loan(2.5, 0, 1000.00);
    }
    catch (IllegalArgumentException ex) {
        ex.getMessage();
    }
}

Scanner input = new Scanner(System.in);
double annualInterestRate;
int numberOfYears;
double loanAmount;
private java.util.Date loanDate;

public Loan() {
    this(2.5, 0, 1000);
}
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() {
    if (annualInterestRate > 0)
        return annualInterestRate;
    else
        throw new IllegalArgumentException("Interest rate cannot be zero or negative.");
}

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

public int getNumberOfYears() {
    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() {
    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

It's not clear what you expect this to do in main :

try {
    Loan(2.5, 0, 1000.00);
}

I suspect you meant it to be a constructor call:

try {
    new Loan(2.5, 0, 1000.00);
}

Your post gives an indication of a bit of confusion over terminology, which may have led to this problem:

I am trying to get the loan class called to the main method

You don't call a class. You call a constructor or a method. What you meant is:

I am trying to make the main method call the constructor for the Loan class.

At that point, it's potentially clearer that you need new .

Answer 2

You need to create a Loan object first with the "new" keyword. This will call the constructor.

Loan loanVar = new Loan(2.5, 0, 1000.00);

Answer 3

To invoke a constructor in your main method you need to use the new keyword. Like you do for initializing loanDate in the Loan constructor.

Answer 4

Your code tries to call a static method called Loan, but it looks like you want to create a new Loan object. You do that by using the keyword new and giving the correct parameters to the constructor:

// create a new Loan using the no-args constructor
Loan defaultLoan = new Loan();
// or create a new Load with the specified rate/duration/amount
Loan myLoan = new Loan(2.5, 0, 1000.0);