字段验证不工作

Question

我是Java的新手。我最近开始了我的第一个项目(计算器)在Net beans。
当我在工作的时候，我给它添加了一个if条件。
if条件检查字段是否为空。

这是我的代码:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    double a, b, c;
    a = Integer.parseInt(jTextField1.getText());
    b = Integer.parseInt(jTextField2.getText());
    if(jTextField1.getText().equals("")) {
        jLabel2.setText("Please enter a number");
    }
    else {
        c = a + b;
        jLabel2.setText("" + c);
    }
}

当我点击带有空字段的按钮时，它会给我一个这样的错误:

run:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:504)
    at java.lang.Integer.parseInt(Integer.java:527)
    at calc.jButton1ActionPerformed(calc.java:132)
    at calc.access$000(calc.java:11)
    at calc$1.actionPerformed(calc.java:53)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3320)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:708)
    at java.awt.EventQueue$4.run(EventQueue.java:706)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

但是当我将if(jTextField1.getText().equals(""))改为if(!jTextField1.getText().equals(""))时，它可以正常工作，但是当我将else条件添加到它的第一部分(不== ")将正常工作。但是第二个(else)会给出错误。

谁能告诉我怎么修理它?

Answer 1

如果没有数据，那么jTextField1.getText()将给您一个空字符串(")和带空字符串的Integer.parseInt("")会给你NumberFormatException因为"不是一个有效的数字。另外你应该检查两个数字所以它应该像这样

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    double a, b, c;
     if (jTextField1.getText().equals("") || jTextField2.getText().equals("")){
          jLabel2.setText("Missing Input");
     }else{
        try{
             a = Integer.parseInt(jTextField1.getText());
             b = Integer.parseInt(jTextField2.getText());
             c = a + b;
             jLabel2.setText("" + c);
          }catch(NumberFormatException e){
             jLabel2.setText("Enter Valid numbers");            
         }
    }
}

简单地把你的代码放在try中，所以如果任何输入不是一个有效的数字，那么控制到catch块并显示错误

Answer 2

将验证更改为在解析数字之前进行:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    int a, b, c;
    if(jTextField1.getText().equals("")) {
        jLabel2.setText("Please enter a number");
    }
    else {
        a = Integer.parseInt(jTextField1.getText());
        b = Integer.parseInt(jTextField2.getText());
        c = a + b;
        jLabel2.setText("" + c);
    }
}

您可能还需要检查其他条件，例如是否输入数字。将文本放在那里也会抛出NumberFormatException。我会将您的验证逻辑更改为如下内容:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    int a, b, c;
    try {
       a = Integer.parseInt(jTextField1.getText());
    } catch (NumberFormatException e) {
       jLabel2.setText("Please enter a number in field1");
       return;
    }
    try {
       b = Integer.parseInt(jTextField2.getText());
    } catch (NumberFormatException e) {
       jLabel2.setText("Please enter a number in field2");
       return;
    }
    c = a + b;
    jLabel2.setText("" + c);
}

Answer 3

你应该用try和catch块来包围你的代码。如果文本字段为空，则不能将其文本解析为整数。

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    int sum = 0;
    int a, b;
    try {
        a = Integer.parseInt(jTextField1.getText());
        sum += a;
    } catch (NumberFormatException e) {
        System.out.println("Please correct your text field number 1");
    }       
    try {
        b = Integer.parseInt(jTextField2.getText());
        sum += b;
    } catch (NumberFormatException e) {
        System.out.println("Please correct your text field number 2");
    }
    jLabel.setText("" + sum);
}