java - 使用带有 Java swing 组件的循环来摊销贷款。

Question

好吧，我对 Java 还很陌生，我已经进入了学习这些东西的第九周了。我将发布一些来自学校项目的源代码 - 这不是完整的源代码 - 这段代码是我分期偿还贷款的循环。我试图从菜单选择(菜单打印到文本字段)或用户输入中摊销。问题是，我无法弄清楚这是数学问题，还是我的循环，是它没有正确摊销贷款。我只是想知道是否有人看到我错过的明显的东西，如果是的话，请您指出，以便我能走上正确的轨道？提前致谢!

来源:

private void amortizeButtonActionPerformed( java.awt.event.ActionEvent evt ) {
  // This module borrowed from Ryan Jones in George Griepp's PRG 420 class.

  NumberFormat nf = NumberFormat.getCurrencyInstance();
  int Monthly = 0;
  int monthcount = 0;
  String Output = "";

  int i = 0; // For first loop
  double loanamount = Double.parseDouble( tempTextField3.getText() );        //all loan amounts  are the same  
  double rate = Double.parseDouble( tempTextField1.getText() );     //Array for the rate
  double time = Double.parseDouble( tempTextField2.getText() );         //Array for the time
  double totalnumpayments = 0;         //Set for 
  double monthlypayment = 0; //Set for math calculation in first loop
  double interestPayment = 0;            //Set for math calculation in first loop
  double totaltime = 0; //Set for second loop to know how long to loop
  double loan = 0; //Set for second loop
  double interestPayment2 = 0; //Set for second loop
  double principlePayment = 0;  //Set for second loop


  for ( i = 0; i < time; i++ ) {//First loop This loops through the arrays and gives the first message listed below three times
    monthlypayment = ( loanamount * ( ( rate / 12 ) / ( 1 - Math.pow( ( 1 + ( rate / 12 ) ), -( time * 12 ) ) ) ) );
    interestPayment = loanamount * ( rate * 100 / 1200 );
    totaltime = ( time * 12 );


    jTextArea1.setText( "" );
    jTextArea1.setText( "This loan has an interest rate of " + ( rate * 100 ) + "%" + " and a starting loan amount of " + nf.format( loanamount ) );
    jTextArea1.setText( "Payment Number\t\t" + "Towards Principle\t\t" + "Towards Interest\t" + "Remaining on loan" );
    jTextArea1.setText( "" ); // Part of the first loop this will appear three times with the math listed above


    System.out.println( totaltime );
    Monthly++;

    Output += ( ( monthcount++ ) + "\t\t\t" + nf.format( principlePayment ) + "\t\t\t" + nf.format( interestPayment2 ) + "\t\t\t" + nf.format( loan - principlePayment ) + "\n" );


    loan = -principlePayment;// Changes the numbers as the loop goes
    interestPayment2 = loan * ( rate * 100 / 1200 );// Changes the numbers as the loop goes
    principlePayment = monthlypayment - interestPayment2;// Changes the numbers as the loop goes

  }
  jTextArea1.setText( Output );
}

Answer 1

有一些事情，可能是个问题，也可能不是问题(我不熟悉 loans 背后的数学原理)。

1. 您在 for 循环中计算了 totaltime，而没有使用 i 变量。因此它总是会产生相同的结果，并且可以在循环外计算
2. 通过在循环内的 jTextArea1 上调用 setText，其中最后一次调用使用空的 String，您不妨清除它在进入 for 循环之前，最终 jTextArea1 将是空的。或者只是删除代码，因为在 for 循环之后，您将文本设置为 Output
3. loan = -principlePayment 是一个奇怪的说法。因此，如果 principlePayment 为正数，loan 将为负数，interestPayment2 也是负数
4. 您最好使用 StringBuilder 来构造您的 Output 变量

我认为第三点对于您的计算来说是最重要的。