java - 在内部类中访问局部变量(java)

Question

编译代码后出现两个错误。

错误是:

1.

  local variable input is accessed within inner class; 
  needs to be declared final
     String name = input.getText();

2.

  local variable c_age is accessed within inner class; 
  needs to be declared final
     Object child_age = c_age.getSelectedItem();

这是我的代码:

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

public class GUI
{
    public static void main(String[] args)
    {
        JFrame frame = new JFrame("Try GUI");
        JLabel l1 = new JLabel("Please Enter Your Child's Name");
        JTextField input = new JTextField("",10);

        JLabel l2 = new JLabel("Choose Your Child's Age");
        String[] age = {"Age","1","2","3","4","5","6"};
        JComboBox c_age = new JComboBox(age);

        JButton button = new JButton("Search");

        JTextArea result = new JTextArea();
        JScrollPane extend_area = new JScrollPane(result);

        button.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                String name = input.getText();
                Object child_age = c_age.getSelectedItem();
            }
        });

        JPanel panel = new JPanel();
        panel.add(l1);
        panel.add(input);
        panel.add(l2);
        panel.add(c_age);
        panel.add(button);
        panel.add(extend_area);
        frame.add(panel);
        frame.setSize(350,350);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

}

我该如何解决这个错误？

Answer 1

你需要声明

JTextField input = new JTextField("",10);

和

JComboBox c_age = new JComboBox(age);

像这样:

final JTextField input = new JTextField("",10);

final JComboBox c_age = new JComboBox(age);

这意味着input 和c_age 不能改变:

Any local variable, used but not declared in an inner class must be definitely assigned before the body of the inner class.

解释取自 The Java Language Specification，Section - 8.1.3 Inner Classes and Enclosing Instances