檢查空的JTextField用戶輸入之前

Question

private class CalculateButtonHandler implements ActionListener{ 

    public CalculateButtonHandler(JTextField initialAmmount, JTextField yearsToMaturity, JTextField interestRate){ 
     double endingBalance; 
     String text = interestRate.getText(); 
     int interestRateInt = Integer.parseInt(text); 

     String text1 = yearsToMaturity.getText(); 
     int yearsToMaturityInt = Integer.parseInt(text); 

     String text2 = initialAmount.getText(); 
     int initialAmountInt = Integer.parseInt(text); 

     endingBalance = initialAmountInt * Math.pow((1 + interestRateInt/1), 1 *   yearsToMaturityInt); 
    } 

    public void actionPerformed(ActionEvent e){ 
    } 
} 

當前運行時錯誤： 異常線程「main」 java.lang.NumberFormatException：對於輸入字符串：「」

我假設的運行 - 發生時間錯誤是因爲程序運行時沒有輸入，用戶沒有機會輸入要解析爲int的字符串。我無法弄清楚如何檢查這一點。

Answer 1

處理按鈕點擊事件的代碼需要在actionPerformed方法中，而不是在構造函數中。

private class CalculateButtonHandler implements ActionListener{ 

    private final JTextField interestRate; 
    private final JTextField yearsToMaturity; 
    private final JTextField interestRate; 

    public CalculateButtonHandler(JTextField initialAmmount, JTextField  yearsToMaturity, JTextField interestRate) { 
     this.initialAmmount = initialAmmount; 
     this.yearsToMaturity = yearsToMaturity; 
     this.interestRate = interestRate; 
    } 

    public void actionPerformed(ActionEvent e){ 
     double endingBalance; 
     String text = interestRate.getText(); 
     int interestRateInt = Integer.parseInt(text); 

     String text1 = yearsToMaturity.getText(); 
     int yearsToMaturityInt = Integer.parseInt(text); 

     String text2 = initialAmount.getText(); 
     int initialAmountInt = Integer.parseInt(text); 

     endingBalance = initialAmountInt * Math.pow((1 + interestRateInt/1), 1 *   yearsToMaturityInt); 
    } 
}