检查空的JTextField用户输入之前

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){ 
    } 
} 

当前运行时错误： 异常线程“main” java.lang.NumberFormatException：对于输入字符串：“”

我假设的运行 - 发生时间错误是因为程序运行时没有输入，用户没有机会输入要解析为int的字符串。我无法弄清楚如何检查这一点。

Answer 1

处理按钮点击事件的代码需要在actionPerformed方法中，而不是在构造函数中。

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); 
    } 
}