这样吗?
JLabel label[10];但是编译时,提示:
']' expected
JLabel label[10];
^
会出错.
JLabel label[10];但是编译时,提示:
']' expected
JLabel label[10];
^
会出错.
解决方案 »
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变量是一样的.
JLabel[] label = new JLabel[10];
JLabel label[] = new JLabel[10];
JLabel[] label = new JLabel[]{label1,label2,label3 };
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class test
{
public static void main(String args[])
{
MyWindow window=new MyWindow();
window.pack();
}
}
class MyWindow extends JFrame implements ActionListener
{
JPanel panel;
JButton button;
MyWindow()
{
JLabel label[] = new JLabel[2];
JTextField text[]=new JTextField[2];
label[0].setText("输入");
label[1].setText("显示");
text[0].setText("text");
panel=new JPanel();
button=new JButton();
Container con=getContentPane();
panel.add(label[0]);
panel.add(text[0]);
panel.add(label[1]);
panel.add(text[1]);
con.add(panel,"North");
con.add(button,"South");
setVisible(true);
button.addActionListener(this);
addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==button)
{
text[1].setText(text[0].getText());
}
}
}F:\Java>javac test.java
test.java:46: cannot resolve symbol
symbol : variable text
location: class MyWindow
text[1].setText(text[0].getText());
^
test.java:46: cannot resolve symbol
symbol : variable text
location: class MyWindow
text[1].setText(text[0].getText());
^
2 errors还是有错??
String[] s=new String[2];
s[0]=new String("2");
s[1]=new String("3");这是个演示道理一样!!!!!
text[0]=new JTextField("1",10);
text[1]=new JTextField("1",10);你是说这样吗?
上面说的未初始化是一个运行期错误,NullPointerException
而不是编译期错误Error
是因为text[]是在MyWindow()中的局部变量,在其他地方是看不到的
应该
class MyWindow{
JLabel[] label; // 在这里直接=new JLabel[2];也可以
JTextField[] text;
MyWindow(){
label = ......
text = .....
}
}
{
...
JLabel[] label;
JTextField[] text;
MyWindow()
{
label=new JLabel[2];
text=new JTextField[2];
label[0]=new JLabel("输入");
label[1]=new JLabel("显示");
text[0]=new JTextField(10);
text[1]=new JTextField(10);
...
这样就可以了,谢了哈!
import java.awt.*;
import java.awt.Label.*;
import java.awt.event.*;
public class test
{
public static void main(String args[])
{
MyWindow window=new MyWindow();
window.pack();
}
}class MyWindow extends JFrame implements ActionListener
{
JPanel panel;
JButton button;
JTextField text[]=new JTextField[2];
MyWindow()
{
JLabel label[] = new JLabel[2];
label[0].setText("输入");
label[1].setText("显示");
text[0].setText("text");
panel=new JPanel();
button=new JButton();
Container con=getContentPane();
panel.add(label[0]);
panel.add(text[0]);
panel.add(label[1]);
panel.add(text[1]);
con.add(panel,"North");
con.add(button,"South");
setVisible(true);
button.addActionListener(this);
addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
} public void actionPerformed(ActionEvent e)
{
if(e.getSource()==button)
{
text[1].setText(text[0].getText());
}
}
}
F:\>javac test.javaF:\>java test
Exception in thread "main" java.lang.NullPointerException
at MyWindow.<init>(test.java:22)
at test.main(test.java:9)那是啥出错
label[1]=new JLabel("The construstor must be done for each of the elements in the array one by one");
text[0]=new JTextField();
text[1]=new JTextField("This has been told before. I said to one of the answer upstairs what he replied was not for what's wrong with your then question, which might only caught a runtime exception NullPointerException. Now that you caught NullPointerException, you better read what he answered");数组初始化的时候
所有基本类型的数组(int float double char boolean short byte long)默认为0(0.0, '\u0000', false....)
其他(Object)为null