java - 如何从其他类获取文本框值？

Question

我有一个关于 JTextField 的问题，每当我想从我的 Student 类获取文本字段值并将其传递给我的另一个类(即 myAction 类)时，我总是会收到 NullPointerException ，我想要发生的是在我单击按钮或 Jbutton 文本字段中的所有数据都将保存到数组中，并且我已经有一个按钮的 Action 监听器并创建一个 myAction 类。

这是我的代码:学生类(主类)

/*

package Student;
import java.util.Scanner;
import javax.swing.*;
import java.awt.event.*;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Student{
    private static Scanner input = new Scanner(System.in);
    public String[] name = {"Lara", "Jerome", "Ferdie", "Jeffrey", "Eduard", "King"};
    public int[] grade = new int[6];
    JFrame frame;
    JLabel label1, label2, label3, label4, label5, label6;
    JPanel panel;
    public JTextField text1, text2, text3, text4, text5, text6;
    JButton button;


    public static void main(String[] args)
    {
        Student myStudent = new Student();
        myStudent.Layout();
        //myStudent.
    }

    public void GetValue()
    {
        grade[0] = Integer.parseInt(text1.getText());
        grade[1] = Integer.parseInt(text2.getText());
        grade[2] = Integer.parseInt(text3.getText());
        grade[3] = Integer.parseInt(text4.getText());
        grade[4] = Integer.parseInt(text5.getText());
        grade[5] = Integer.parseInt(text6.getText());

        for(int i = 0; i < grade.length; i++)
        {
            System.out.println(grade[i]);
        }
    }

    public void Layout()
    {
        //Design Layout
        panel = new JPanel();
        panel.setLayout(null);
        frame = new JFrame("Student Grades");
        button = new JButton("Get Grade");
        button.setBounds(50, 260, 200, 30);
        label1 = new JLabel("Your Grade: " + name[0]);
        label1.setBounds(10, 10, 150, 30);
        text1 = new JTextField(5);
        text1.setBounds(140, 15, 150, 20);
        label2 = new JLabel("Your Grade: " + name[1]);
        label2.setBounds(10, 50, 150, 30);
        text2 = new JTextField(5);
        text2.setBounds(140, 55, 150, 20);
        label3 = new JLabel("Your Grade: " + name[2]);
        label3.setBounds(10, 90, 150, 30);
        text3 = new JTextField(5);
        text3.setBounds(140, 95, 150, 20);
        label4 = new JLabel("Your Grade: " + name[3]);
        label4.setBounds(10, 130, 150, 30);
        text4 = new JTextField(5);
        text4.setBounds(140, 135, 150, 20);
        label5 = new JLabel("Your Grade: " + name[4]);
        label5.setBounds(10, 170, 150, 30);
        text5 = new JTextField(5);
        text5.setBounds(140, 175, 150, 20);
        label6 = new JLabel("Your Grade: " + name[5]);
        label6.setBounds(10,210, 150, 30);
        text6 = new JTextField(5);
        text6.setBounds(140, 215, 150, 20);
        frame.setSize(350, 350);
        frame.setVisible(true);
        panel.add(label1);
        panel.add(text1);
        panel.add(label2);
        panel.add(text2);
        panel.add(label3);
        panel.add(text3);
        panel.add(label4);
        panel.add(text4);
        panel.add(label5);
        panel.add(text5);
        panel.add(label6);
        panel.add(text6);
        panel.add(button);
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        MyEvent myAction = new MyEvent();
        button.addActionListener(myAction);
    }

}

and my class myAction(or actionlistener) class

class MyEvent implements ActionListener
{
    public void actionPerformed(ActionEvent e) 
    {
      if(e.getActionCommand().equals("Get Grade"))
      {
          Student EventStudent = new Student();
          EventStudent.GetValue();

      }
    }   
}

*/这是我所有的代码希望你能帮助我。

Answer 1

代码中的问题是您在 main 中创建了一个 Student 对象。因此您的文本字段与该对象关联。现在在您的事件监听器中，您正在创建不属于任何组件的另一个学生对象你需要。你必须在 main 方法中从对象中检索数据。请按照下面的操作。希望它会有所帮助。

import java.util.Scanner;
import javax.swing.*;
import java.awt.event.*;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Student{
    static Student myStudent ;
    private static Scanner input = new Scanner(System.in);
    public String[] name = {"Lara", "Jerome", "Ferdie", "Jeffrey", "Eduard", "King"};
    public int[] grade = new int[6];
    JFrame frame;
    JLabel label1, label2, label3, label4, label5, label6;
    JPanel panel;
    public JTextField text1, text2, text3, text4, text5, text6;
    JButton button;


    public static void main(String[] args)
    {
         myStudent = new Student();
         myStudent.Layout();
        //myStudent.
    }

    public void GetValue()
    {
        grade[0] = Integer.parseInt(text1.getText());
        grade[1] = Integer.parseInt(text2.getText());
        grade[2] = Integer.parseInt(text3.getText());
        grade[3] = Integer.parseInt(text4.getText());
        grade[4] = Integer.parseInt(text5.getText());
        grade[5] = Integer.parseInt(text6.getText());

        for(int i = 0; i < grade.length; i++)
        {
            System.out.println(grade[i]);
        }
    }

    public void Layout()
    {
        //Design Layout
        panel = new JPanel();
        panel.setLayout(null);
        frame = new JFrame("Student Grades");
        button = new JButton("Get Grade");
        button.setBounds(50, 260, 200, 30);
        label1 = new JLabel("Your Grade: " + name[0]);
        label1.setBounds(10, 10, 150, 30);
        text1 = new JTextField(5);
        text1.setBounds(140, 15, 150, 20);
        label2 = new JLabel("Your Grade: " + name[1]);
        label2.setBounds(10, 50, 150, 30);
        text2 = new JTextField(5);
        text2.setBounds(140, 55, 150, 20);
        label3 = new JLabel("Your Grade: " + name[2]);
        label3.setBounds(10, 90, 150, 30);
        text3 = new JTextField(5);
        text3.setBounds(140, 95, 150, 20);
        label4 = new JLabel("Your Grade: " + name[3]);
        label4.setBounds(10, 130, 150, 30);
        text4 = new JTextField(5);
        text4.setBounds(140, 135, 150, 20);
        label5 = new JLabel("Your Grade: " + name[4]);
        label5.setBounds(10, 170, 150, 30);
        text5 = new JTextField(5);
        text5.setBounds(140, 175, 150, 20);
        label6 = new JLabel("Your Grade: " + name[5]);
        label6.setBounds(10,210, 150, 30);
        text6 = new JTextField(5);
        text6.setBounds(140, 215, 150, 20);
        frame.setSize(350, 350);
        frame.setVisible(true);
        panel.add(label1);
        panel.add(text1);
        panel.add(label2);
        panel.add(text2);
        panel.add(label3);
        panel.add(text3);
        panel.add(label4);
        panel.add(text4);
        panel.add(label5);
        panel.add(text5);
        panel.add(label6);
        panel.add(text6);
        panel.add(button);
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        MyEvent myAction = new MyEvent(myStudent);
        button.addActionListener(myAction);
    }

}
class MyEvent implements ActionListener
{
    Student myStudent;
    public MyEvent(Student myStudent) {
        this.myStudent=myStudent;
    }

    public void actionPerformed(ActionEvent e) 
    {
      if(e.getActionCommand().equals("Get Grade"))
      {

         myStudent.GetValue();

      }
    }   
}