修改数组中的标签[重复]

Question

我们希望能够更改 JLabel 数组上的文本/图像，但我们无法理解为什么它不起作用。

import java.awt.*;

class layoutWindow extends JFrame implements ActionListener {`



    String[] classStrings = { "EN1A", "EN2A", "EN3A", "EN1B", "EN2B", "EN3B",
            "ES1A", "ES2A", "ES3A", "ES1B", "ES2B", "ES3B", "H1", "H2", "H3",
            "N1A", "N1B", "N1C", "N1D", "N1E", "N2A", "N2B", "N2C", "N2D",
            "N2E","N3A","N3B","N3C","N3D","S1A","S1B","S2A","S2B","S3A","S3B" };
    String[] FormationStrings = { "3-3-3", "3-3-2", "2-4-2", "4-4", "2-2-2-2","3-4-3" };
    // Create the combo box, select item at index 4.

     JLabel[] deskLabels = new JLabel[96];



    JComboBox classList = new JComboBox(classStrings);
    JComboBox formationList = new JComboBox(FormationStrings);


    JButton seatbButton = new JButton(" randomize");
    JButton backButton = new JButton("back");
    JButton groupButton = new JButton("Make groups");

    JLabel classLabel = new JLabel("choose class");
    JLabel formationLabel = new JLabel("choose formation");

    JPanel layoutPanel = new JPanel(new GridLayout(8, 12, 1,15));
    JPanel top = new JPanel(new GridLayout(1, 2, 15,1));



    public layoutWindow() {
        super("layout Example");
        setExtendedState(JFrame.MAXIMIZED_BOTH);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setVisible(true);
        Container contentArea = getContentPane();

        top.setVisible(true);
        layoutPanel.setVisible(true);

            int i = 1;
            for (JLabel label : deskLabels) {
                label = new JLabel();
                if ((i % 12) != 100) {
                    label.setText("" + i);
                    layoutPanel.add(label);}
                else {
                    label.setText("  ");
                    layoutPanel.add(label);
                }
                i++;
     }

        top.add(backButton);
        top.add(classLabel);
        top.add(classList);
        top.add(formationLabel);
        top.add(formationList);
        top.add(seatbButton);

        contentArea.add("North", top);
        contentArea.add("Center", layoutPanel);

        setContentPane(contentArea);
        formationList.addActionListener(this);
        classList.addActionListener(this);
        backButton.addActionListener(this);

    }

    @Override
    public void actionPerformed(ActionEvent event) {


        String string = (String) formationList.getSelectedItem();

         if(string == "4-4"){
            deskLabels[5].setText("aasdggnmh");

         }
        }
        }

布局任务窗口

public class layouttaskwindow {

    public static void main(String[] args) {

        layoutWindow win = new layoutWindow();
    }

}

我们不明白为什么这不起作用。我们使用 for 循环从数组中创建所有标签，但是当我们尝试更改它们时它不起作用。我们试图在 ActionEvent 中更改它但我们没有得到回应，有人可以解释一下如何解决这个问题吗？

Answer 1

我也认为（就像 Hackerdarshi 说的，我没看过帖子，但看起来不错）问题是由 foreach 循环引起的。不确定，但我认为 Java 没有给你正确的参考。所以要修复它，你可以试试这个：

        for (int i = 0; i < deskLabels.length; i++) {
                deskLabels[i] = new JLabel();
                if ((i % 12) != 100) deskLabels[i].setText("" + i);
                else deskLabels[i].setText("  ");
                layoutPanel.add(deskLabels[i]);
     }

正如伯杰所说，另一个问题是：string == "4-4" 无需深入（for more read this）：当您使用 == 时，通常会按值进行比较。但是字符串是对象，所以在对象上调用 == 会比较它的引用而不是它的值。在 Java 中，字符串是特殊的。因此，这取决于他们如何初始化 == 返回的内容。所以只需使用

string.equals("4-4") 

如果你想比较一个String的值