Java while循环画线

Question

大家好，我正在尝试做一个 Java 书中的练习，我需要做的是画线，在文本字段中我必须说明线之间的距离必须有多远。所有这些都必须在循环中，因此没有硬编码行。

我已经按照我认为应该完成的方式进行了所有操作，但是我的控制台中不断出现一些奇怪的错误。错误代码如下:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48) at java.lang.Integer.parseInt(Integer.java:470) at java.lang.Integer.parseInt(Integer.java:499) at h03.LinePanel.paintComponent(LinePanel.java:30) at javax.swing.JComponent.paint(JComponent.java:1037) at javax.swing.JComponent._paintImmediately(JComponent.java:5106) at javax.swing.JComponent.paintImmediately(JComponent.java:4890) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:812) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:714) at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:694) at javax.swing.RepaintManager.access$700(RepaintManager.java:41) at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1672) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:702) at java.awt.EventQueue.access$400(EventQueue.java:82) at java.awt.EventQueue$2.run(EventQueue.java:663) at java.awt.EventQueue$2.run(EventQueue.java:661) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87) at java.awt.EventQueue.dispatchEvent(EventQueue.java:672) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

由于我是 Java 新手，所以我不知道我做错了什么以及如何解决此错误，因此我将不胜感激!我在面板中使用的代码是

DrawLines lines = new DrawLines();

public void paintComponent(Graphics g) {

    super.paintComponent(g);
    int positionY = getHeight() - Integer.parseInt(afstand.getText()); // absolut positioning

    int yPos = 0;

    while(yPos <= positionY) {

        lines.drawLines(g, 0, yPos, getWidth(), yPos);
        yPos = yPos + Integer.parseInt(afstand.getText());
    }

}

public void actionPerformed(ActionEvent e) {

    try {

        repaint();


    }
    catch(NumberFormatException err) {

        JOptionPane.showMessageDialog(null, "something went wrong! heeft u wel    een waarde opgegeven?");

    }

}

Answer 1

问题正是它所说的:您在空字符串上调用 Integer.parseInt() ，在您的示例中:afstand.getText()，它确实不喜欢。

java.lang.NumberFormatException: For input string: "" at
[...]
java.lang.Integer.parseInt(Integer.java:470) at java.lang.Integer.parseInt(Integer.java:499)

要避免异常，您可以捕获异常:

try {
    int input = Integer.parseInt(afstand.getText());
    //rest of your code
} catch (NumberFormatException e) {
    //let the use know that the entry is invalid
}