我似乎在“创建按钮”处理程序的操作监听器中设置了一些错误。当我尝试获取文本字段 nameTF 的值时,出现空指针错误。我尝试模仿您的计算器代码,退出按钮处理程序运行良好。我知道按“创建”按钮会调用处理程序,但语句
inName = nameTF.getText();
给出错误消息。
监听器的完整文本为
private class CreateButtonHandler
implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
String inName, inType; //local variables
int inAge;
Dog arf;
inName = nameTF.getText();
inType = typeTF.getText();
inAge = Integer.parseInt( ageTF.getText() );
//System.out.println("Inside CreateButtonHandler");
System.out.println(inName);
arf = new Dog(inName, inType, inAge);
System.out.println(arf.toString () );
}
}
整个程序如下。任何帮助/解释/建议将非常受欢迎。
import javax.swing.*; // import statement for the GUI components
import java.awt.*; //import statement for container class
import java.awt.event.*;
public class DogGUI //creation of DogGUI clas
{
private JLabel nameL, typeL, ageL, outtputL;
private JTextField nameTF, typeTF, ageTF;
private JButton createB, exitB;
CreateButtonHandler cbHandler;
ExitButtonHandler ebHandler;
public void driver () //creates everything
{
//create the window
JFrame DogInfo = new JFrame ("Dog GUI");
DogInfo.setSize(400,300); //set the pixels for GUI
DogInfo.setVisible(true); // set visibility to true
DogInfo.setDefaultCloseOperation(DogInfo.EXIT_ON_CLOSE); // when closed JFrame will disappear
//layout
Container DogFields = DogInfo.getContentPane();
DogFields.setLayout(new GridLayout(5,2));
// setting labels for GUI
nameL = new JLabel ("Enter name of Dog: ",
SwingConstants.RIGHT);
typeL = new JLabel ("Enter the type of the Dog: ",
SwingConstants.RIGHT);
ageL = new JLabel ("Enter the age of the Dog: ",
SwingConstants.RIGHT);
outtputL = new JLabel ("Dog Information: ",
SwingConstants.RIGHT);
//Buttons
JButton createB, exitB; //creating button for creation of Dog and button to exit
createB = new JButton("Create Dog");
exitB = new JButton("Exit");
//text fields
JTextField nameTF, typeTF, ageTF, outtputTF;
nameTF = new JTextField(10);
typeTF = new JTextField(15);
ageTF = new JTextField(5);
outtputTF = new JTextField(25);
outtputTF.setEditable(false); //this TF is to display this output
//Lables and Textfields
DogInfo.add(nameL);
DogInfo.add(nameTF);
DogInfo.add(typeL);
DogInfo.add(typeTF);
DogInfo.add(ageL);
DogInfo.add(ageTF);
DogInfo.add(outtputL);
DogInfo.add(outtputTF);
//Buttons
DogInfo.add(createB);
DogInfo.add(exitB);
//Instantiate Listeners
cbHandler = new CreateButtonHandler();
ebHandler = new ExitButtonHandler();
//Register Listeners
createB.addActionListener(cbHandler);
exitB.addActionListener(ebHandler);
DogInfo.setVisible(true);
}
//run the program from main, instantiate class, invoke driver() method
public static void main(String[] args)
{
DogGUI d = new DogGUI();
d.driver();
}
// class to actually handle Dog creation
private class CreateButtonHandler
implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
String inName, inType; //local variables
int inAge;
Dog arf;
inName = nameTF.getText();
inType = typeTF.getText();
inAge = Integer.parseInt( ageTF.getText() );
//System.out.println("Inside CreateButtonHandler");
System.out.println(inName);
arf = new Dog(inName, inType, inAge);
System.out.println(arf.toString () );
}
}
private class ExitButtonHandler
implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
System.out.println("inside exit button");
System.exit(0);
} // end method actionPerformed
}
}
最佳答案
您在 driver()
方法中有一个名为 nameTF
的局部变量,它隐藏了该字段(对于其他一些变量也是如此)。
JTextField nameTF, typeTF, ageTF, outtputTF;
nameTF = new JTextField(10);
删除这些字段的声明,因为它们已被声明为实例字段。
private JTextField nameTF, typeTF, ageTF;
(可能不是 outtputTF
,具体取决于您想要执行的操作)
关于Java GUI 变量问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16682780/