java 数组文本字段
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array TextField
提问by giovedy
Na is a parameter. I'm sure that this parameter is correct. I've declared an array of Na JTextField, And I would like to use one of them. But when I run my code, There is an exception...
Na 是一个参数。我确定这个参数是正确的。我已经声明了一个 Na JTextField 数组，我想使用其中一个。但是当我运行我的代码时，有一个例外......
That's my code :
那是我的代码：
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
class Panneau_fenetre1A extends JPanel
{
public Panneau_fenetre1A(int Na)
{
JTextField[] allField = new JTextField [Na];
for(int i = 0;i<Na;i++)
{
allField[i].setText(String.valueOf(0));
allField[i].setBounds(150, 350+i*25,20, 20);
}
}
}
That's the exception :
那是例外：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Panneau_fenetre1A.<init>(Panneau_fenetre1A.java:18)
at Cadre_fenetre1A.<init>(Cadre_fenetre1A.java:13)
at Panneau_fenetre$ecout1.actionPerformed(Panneau_fenetre.java:64)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2012)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2335)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:404)
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:6268)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6033)
at java.awt.Container.processEvent(Container.java:2045)
at java.awt.Component.dispatchEventImpl(Component.java:4629)
at java.awt.Container.dispatchEventImpl(Container.java:2103)
at java.awt.Component.dispatchEvent(Component.java:4455)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4633)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4297)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4227)
at java.awt.Container.dispatchEventImpl(Container.java:2089)
at java.awt.Window.dispatchEventImpl(Window.java:2517)
at java.awt.Component.dispatchEvent(Component.java:4455)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:649)
at java.awt.EventQueue.accessfor(int i = 0;i < Na;i++)
{
JTextField textField = new JTextField(String.valueOf(0));
textField.setBounds(150, 350 + i * 25, 20, 20);
allField[i] = textField;
}
0(EventQueue.java:96)
at java.awt.EventQueue.run(EventQueue.java:608)
at java.awt.EventQueue.run(EventQueue.java:606)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext.doIntersectionPrivilege(AccessControlContext.java:105)
at java.security.AccessControlContext.doIntersectionPrivilege(AccessControlContext.java:116)
at java.awt.EventQueue.run(EventQueue.java:622)
at java.awt.EventQueue.run(EventQueue.java:620)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext.doIntersectionPrivilege(AccessControlContext.java:105)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:619)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
回答by mre
You've failed to properly initialize your array. Therefore, allField[i] = nullfor all i < Na. Hence the NullPointerException. The following will work,
您未能正确初始化您的阵列。因此，allField[i] = null对于所有i < Na. 因此NullPointerException。以下将起作用，
JTextField[] allField = new JTextField [Na];
回答by FloatingCoder
This line...
这条线...
for(int i = 0;i < Na;i++)
{
allField[i] = new JTextField(String.valueOf(0));
allField[i].setBounds(150, 350 + i * 25, 20, 20);
}
initializes a new ARRAY, which will hold JTextField objects. The array has -Na- spaces in it, but each space is still empty. You still need to create the JTextField object to go into the empty array spaces.
初始化一个新的 ARRAY，它将保存 JTextField 对象。数组中有 -Na- 空格，但每个空格仍然是空的。您仍然需要创建 JTextField 对象以进入空数组空间。
Something like this should work...
像这样的事情应该工作......
##代码##