我有 4 個不同的 JLabels 和兩個按鈕，一個按鈕應該將顏色向右更改為藍色，另一個按鈕將顏色更改回來

Question

我試圖通過單擊按鈕（actionEvent）來實現它，顏色將 label 更改為藍色。 我有四個不同的標簽和兩個按鈕。 如果單擊帶有右側箭頭的按鈕，則如果再次單擊該按鈕，則右側的 label 將從橙色變為藍色，依此類推。 如果單擊左側的按鈕，則再次單擊左側的 label 將從橙色變為藍色，依此類推。 我不知道我是否在動作偵聽器中做錯了什么，但是當單擊按鈕時沒有任何反應。我將在本段下方發布分配說明，因此希望它更有意義。

在本實驗中，您將創建一個類似於下圖的 GUI。 在左側，您有一個包含兩個按鈕的控制面板：一個帶有左箭頭，一個帶有右箭頭。 每當您單擊右箭頭時，藍色瓷磚就會向右移動（數字保持不變） 每當您單擊向左箭頭時，藍色瓷磚就會向左移動。 如果藍色方塊在 position 1 上並單擊左箭頭，則藍色方塊移動到最右側（位置 4） 右箭頭類似。

所需的 Output：

package guiLayout;

/**
 * In this JFrame my goal is to be able to make the color of the labels
 * change on the JButton click with an action listener.
 * 
 * @author Kody Berry
 * @since 7-4-2020
 */

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import java.awt.Color;
import javax.swing.JButton;
import java.awt.Font;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class LabGuiLayout extends JFrame {
// Fields
private static final long serialVersionUID = 1L;
private JPanel contentPane;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                LabGuiLayout frame = new LabGuiLayout();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public LabGuiLayout() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 500, 200);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    // Creating instances of methods and adding it to JPannel.
    JButton btnNewButton = moveLeftButton();
    contentPane.add(btnNewButton);

    JLabel lblNewLabel = labelOne();
    contentPane.add(lblNewLabel);

    JLabel lblNewLabel_1 = labelTwo();
    contentPane.add(lblNewLabel_1);

    JLabel lblNewLabel_2 = labelThree();
    contentPane.add(lblNewLabel_2);

    JButton button = moveRightButton();
    contentPane.add(button);

    JLabel label = labelFour();
    contentPane.add(label);

    JLabel lblNewLabel_3 = demoLayoutLabel();
    contentPane.add(lblNewLabel_3);
}

/**
 * Title Label.
 * 
 * @return Returns lblNewLabel_3.
 */
private JLabel demoLayoutLabel() {
    JLabel lblNewLabel_3 = new JLabel("Demo Layout");
    lblNewLabel_3.setFont(new Font("Tahoma", Font.PLAIN, 23));
    lblNewLabel_3.setHorizontalAlignment(SwingConstants.CENTER);
    lblNewLabel_3.setOpaque(true);
    lblNewLabel_3.setBounds(0, 0, 490, 46);
    return lblNewLabel_3;
}

/**
 * Number 1 label.
 * 
 * @return Returns lblNewLabel.
 */
private JLabel labelOne() {
    JLabel lblNewLabel = new JLabel(" 1");
    lblNewLabel.setFont(new Font("Tahoma", Font.PLAIN, 26));
    lblNewLabel.setOpaque(true);
    lblNewLabel.setBounds(91, 45, 86, 93);
    lblNewLabel.setBackground(Color.BLUE);
    lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
    return lblNewLabel;
}

/**
 * Number 2 label.
 * 
 * @return Returns lblNewLabel_1.
 */
private JLabel labelTwo() {
    JLabel lblNewLabel_1 = new JLabel("2");
    lblNewLabel_1.setFont(new Font("Tahoma", Font.PLAIN, 26));
    lblNewLabel_1.setOpaque(true);
    lblNewLabel_1.setBounds(187, 45, 86, 93);
    lblNewLabel_1.setBackground(Color.ORANGE);
    lblNewLabel_1.setHorizontalAlignment(SwingConstants.CENTER);
    return lblNewLabel_1;
}

/**
 * Number 3 label.
 * 
 * @return Returns lblNewLabel_2.
 */
private JLabel labelThree() {
    JLabel lblNewLabel_2 = new JLabel("3");
    lblNewLabel_2.setFont(new Font("Tahoma", Font.PLAIN, 26));
    lblNewLabel_2.setOpaque(true);
    lblNewLabel_2.setBounds(283, 45, 86, 93);
    lblNewLabel_2.setBackground(Color.ORANGE);
    lblNewLabel_2.setHorizontalAlignment(SwingConstants.CENTER);
    return lblNewLabel_2;
}

/**
 * Number 4 label.
 * 
 * @return Returns label.
 */
private JLabel labelFour() {
    JLabel label = new JLabel("4");
    label.setFont(new Font("Tahoma", Font.PLAIN, 26));
    label.setOpaque(true);
    label.setHorizontalAlignment(SwingConstants.CENTER);
    label.setBackground(Color.ORANGE);
    label.setBounds(379, 45, 86, 93);
    return label;
}

/**
 * Move to the left button that when clicked will change the button to the left
 * to blue and the previous button to orange. Once the last label on the left is
 * blue if the button is clicked again it will start over.
 * 
 * @return Returns btnNewButton.
 */
private JButton moveLeftButton() {

    // Array of labels.
    JLabel[] jl = { labelOne(), labelTwo(), labelThree(), labelFour() };

    JButton btnNewButton = new JButton("<--");

    btnNewButton.addActionListener(new ActionListener() {
        int clicks = 0;

        public void actionPerformed(ActionEvent e) {
            switch (++clicks) {
            case 1:
                jl[0].setBackground(Color.ORANGE);
                jl[3].setBackground(Color.BLUE);
                break;
            case 2:
                jl[3].setBackground(Color.ORANGE);
                jl[2].setBackground(Color.BLUE);
                break;
            case 3:
                jl[2].setBackground(Color.ORANGE);
                jl[1].setBackground(Color.BLUE);
                break;
            case 4:
                jl[1].setBackground(Color.BLUE);
                jl[0].setBackground(Color.ORANGE);
                break;
            default:
                clicks = 1;
                break;
            }

        }
    });
    btnNewButton.setBounds(32, 45, 49, 23);
    return btnNewButton;
}

/**
 * Move to the right button that when clicked will change the button to the
 * right to blue and the previous button to orange. Once the last label on the
 * right is blue if the button is clicked again it will start over.
 * 
 * @return Returns button.
 */
private JButton moveRightButton() {

    // Array of labels.
    JLabel[] jl = { labelOne(), labelTwo(), labelThree(), labelFour() };

    JButton button = new JButton("-->");

    button.addActionListener(new ActionListener() {
        int clicks = 0;

        public void actionPerformed(ActionEvent e) {
            switch (++clicks) {
            case 1:
                jl[0].setBackground(Color.ORANGE);
                jl[1].setBackground(Color.BLUE);
                break;
            case 2:
                jl[1].setBackground(Color.ORANGE);
                jl[2].setBackground(Color.BLUE);
                break;
            case 3:
                jl[2].setBackground(Color.ORANGE);
                jl[3].setBackground(Color.BLUE);
                break;
            case 4:
                jl[0].setBackground(Color.BLUE);
                jl[1].setBackground(Color.ORANGE);
                break;
            default:
                clicks = 1;
                break;
            }
        }
    });
    button.setBounds(32, 79, 49, 23);
    return button;
}

}

Answer 1

JLabel lblNewLabel = labelOne();
contentPane.add(lblNewLabel);

您創建 label 並將其添加到框架。

但是在 ActionListener 你有：

JLabel[] jl = { labelOne(), labelTwo(), labelThree(), labelFour() };

它為每個 label 創建 4 個新實例。 這些標簽不會添加到框架中，因此更改它們的背景沒有任何作用。

相反，您需要將 Array 定義為 class 的實例變量。 然后您的 ActionListener 可以從 Array 訪問 label。

因此，在構造函數中，當您創建 label 並將其添加到框架時，您還需要將其添加到數組中。