Java程序错误：找不到符号

Question

我迷路了！我正在上一门在线Java课程，需要帮助完成这项任务。 一旦程序编译，它就会产生一个找不到符号的错误

Loan loan = new Loan(annualInterestRate, numberOfYears, loanAmount);
symbol:   class Loan
location: class ChangeRequest5

我尝试在类ChangeRequest5中创建类Loan，以及getMonthlyPaymen的方法。该程序运行一个干净且成功的构建，并为利率，贷款期限和贷款金额创建用户输入，但不会显示该表。

import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

 public class ChangeRequest5 {

   public static void main(String[] args) {
    Object[] rateList = new Object[9];
    int i = 0;
    for (double rate = 5; rate <=6; rate += 1.0 /4)
        rateList[i++] = new Double (rate);

    Object annualInterestRateObject = JOptionPane.showInputDialog(
            null, "Select annual interest rate:" , "Mortgage Calculator" ,
            JOptionPane.QUESTION_MESSAGE, null, rateList, null);

    double annualInterestRate =
            ((Double)annualInterestRateObject).doubleValue();

    Object[]yearList = {new Integer(7), new Integer(15), new Integer(30)};

    Object numberOfYearsObject = JOptionPane.showInputDialog(
            null, "Select number of years:" , "Mortgage Calculator" ,
            JOptionPane.QUESTION_MESSAGE, null, yearList, null);
            int numberOfYears = ((Integer)numberOfYearsObject).intValue();

    String loanAmountString = JOptionPane.showInputDialog(null,
            "Enter loan amount, for example  200000  for $200000.00" , "Mortgage Calculator" , 
              JOptionPane.QUESTION_MESSAGE);
    double loanAmount = Double.parseDouble(loanAmountString);


    Loan loan = new Loan(annualInterestRate, numberOfYears, loanAmount);
    double monthlyPayment = loan.getMonthlyPayment();


    String output = "Interest Rate:" + annualInterestRate + 
            "%" + "Number of Years:" + numberOfYears + " Loan Amount: $"
            + loanAmount;
    output += " Monthly Payment: " + "$" + (int)(monthlyPayment * 100) /100.0;
    output += " Totaly Payment $" + (int) (monthlyPayment * 12 * numberOfYears
            * 100) / 100.0;

    double monthlyInterestRate = annualInterestRate / 1200;

    double balance = loanAmount;
    double interest;
    double principal;

    output += " Payment#\tInterest\rPrincipal\tBalance";

    for (i = 1; i <= numberOfYears * 12; i++){
      interest = (int)(monthlyInterestRate * balance * 100) / 100.0;
      principal = (int)((monthlyPayment - interest) * 100) / 100.0;
      balance = (int)((balance - principal) * 100) / 100.0;

      output += i + "\t" + interest + "\t" + principal + "\t" + balance;
    }

    JScrollPane jsp = new JScrollPane(new JTextArea(output));
    jsp.setPreferredSize(new java.awt.Dimension(400, 200));
    JOptionPane.showMessageDialog(null, jsp,
        "Mortgage Calculator" , JOptionPane.INFORMATION_MESSAGE, null);
    }

}

Answer 1

您是否在同一个包中定义了一个类Loan.java的文件Loan？如果它在同一个包装中，它应该可以工作。

如果它位于不同的包中，则需要将其导入到其他.java文件中：

import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import package2.Loan;

 public class ChangeRequest5 {

Answer 2

您需要拥有＆＃39;贷款＆＃39;的进口对帐单。除非它在同一个包中