使用Java swing組件循環分期償還貸款。

Question

好吧，我還是Java的新手，我正在做這個東西的第九周。我將發佈學校項目的一些源代碼 - 這不是完整的源代碼 - 這部分代碼是我的循環來分期償還貸款。我試圖從菜單選擇（菜單打印到文本字段）或用戶輸入中攤銷。問題是，我無法弄清楚它是數學還是我的循環，它不是在正確地分期償還貸款。我只想知道是否有人看到我錯過的東西，如果有的話，請你指出來，以便我可以走上正確的軌道？提前致謝！

來源：

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

有幾件事情，這可能是一個問題或沒有（我不熟悉的背後loans的數學）。

1. 你在你的for -loop計算totaltime，而不使用的i變量。因此，它總是會產生相同的結果，並且可以循環
2. 外面來計算通過調用循環，你的最後一次通話是空String內jTextArea1setText，你還不如進入for之前就明確表示迴圈，因爲最後jTextArea1將只是空的。或者只是刪除代碼，因爲在for循環後，您將文本設置爲Output
3. loan = -principlePayment是一個奇怪的聲明。因此，如果principlePayment是正數，loan將是一個負數，並且interestPayment2以及
4. 你最好使用StringBuilder來構建你的Output變量

我覺得數字3是你最重要的計算。