Question

尝试运行程序时出现错误，因为找不到我的方法。这是第一个错误代码：

Error: cannot find symbol 
  symbol: method getSelectedItem()
  location: variable event of type java.awt.event.ActionEvent

这是第二个错误代码：

Error: cannot find symbol
  symbol:   method setBackground(java.awt.Color)
  location: variable x of type java.lang.Object

以下是程序代码：

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

public class PanelColor extends JFrame implements ActionListener{
  // Declare all instance data  (primitives and objects used) 
  private int WIDTH = 501;
  private int HEIGHT = 501;
  JPanel panelN;
  JPanel panelS;
  JPanel panelE;
  JPanel panelW;
  JPanel panelC;
  Container con; 
  JComboBox  box;
  Dimension dPN;
  Dimension dPS;
  Dimension dPE;
  Dimension dPW;
  Dimension dPC;

//constructor 
  public PanelColor(){
    super("Panel Color"); 
    con = getContentPane(); 
    con.setLayout(new BorderLayout()); 
    setSize(WIDTH, HEIGHT);

    panelN = new JPanel();
    panelS = new JPanel();
    panelE = new JPanel();
    panelW = new JPanel();
    panelC = new JPanel();
    dPC = new Dimension(25,25);
    dPS = new Dimension(200,200);
    dPE = new Dimension(400,200);
    dPW = new Dimension(400,200);
    dPN = new Dimension(200,200);
    panelC.setBackground(Color.RED);
    panelN.setBackground(Color.YELLOW);
    panelE.setBackground(Color.BLUE);
    panelW.setBackground(Color.GREEN);
    panelS.setBackground(Color.MAGENTA);
    panelC.setPreferredSize(dPC);
    panelN.setPreferredSize(dPN);
    panelE.setPreferredSize(dPE);
    panelW.setPreferredSize(dPW);
    panelS.setPreferredSize(dPS);
    box = new JComboBox();
    box.addItem("Panel North");
    box.addItem("Panel South");
    box.addItem("Panel East");
    box.addItem("Panel West");
    box.addItem("Panel Center");
    box.addActionListener(this);
    con.add(panelC, BorderLayout.CENTER);
    con.add(panelE, BorderLayout.EAST);
    con.add(panelW, BorderLayout.WEST);
    con.add(panelN, BorderLayout.NORTH);
    con.add(panelS, BorderLayout.SOUTH);
    con.add(box, BorderLayout.CENTER);

    setVisible(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
}

  public void actionPerformed(ActionEvent event){
    Object source = event.getSource();
    Random r = new Random();
      int  red = r.nextInt(255) + 1;
      int  green = r.nextInt(255) + 1;
      int  blue = r.nextInt(255) + 1;
      Color c = new Color(red, green, blue);
      String text = event.getSelectedItem();
      Object x = event.getSelectedItem();
      if(source == text){
        x.setBackground(c);
      }
  }

  public static void main(String[] args){
    PanelColor object = new PanelColor(); 
  }
}

我知道有很多关于找不到符号错误的帖子，但通过我所看到的所有帖子，他们都没有帮我解决这个问题。 我想知道为什么它会给我这些错误？以及如何修复它以便我知道以供将来参考。错误所在的区域列在本段下方。我希望如果他们遇到类似问题，也可以帮助其他人。

这些是有错误的区域：

String text = event.getSelectedItem();

Object x = event.getSelectedItem();

if(source == text){
  x.setBackground(c);
}

Answer 1

getSelectedItem是JComboBox而不是ActionEvent

的方法

JComboBox comboBox = (JComboBox) event.getSource();
...

String text = comboBox.getSelectedItem().toString();

Answer 2

问题在于getSelectedItem();类

中定义了ActionEvent

您需要将其更改为：

String text = (String) box.getSelectedItem();

找不到符号错误。找不到getSelectedItem（）和setBackground（）方法

2 个答案: