如何在指定的布局中放置JLabel？

Question

我试图将我的标签和按钮放在屏幕上。 我在这里找到了一个使用以下label3.setHorizontalAlignment(SwingConstants.CENTER); label3.setVerticalAlignment(SwingConstants.CENTER);设置标签位置的答案： label3.setHorizontalAlignment(SwingConstants.CENTER); label3.setVerticalAlignment(SwingConstants.CENTER); label3.setHorizontalAlignment(SwingConstants.CENTER); label3.setVerticalAlignment(SwingConstants.CENTER); 但是我的代码没有任何作用。

另外，将我的布局从“流布局”更改为“边界布局”时，屏幕上仅出现一个Jbutton [CLEAR]。 谁能帮我纠正这个问题？

public class Corrected1 extends JFrame {

    public JTextField tf1;
    public JTextField tf2;
    public JLabel label1;
    public JLabel label2;
    public JLabel label3;
    public JLabel label4;
    public JButton button1;
    public JButton button2;
    public JComboBox cb,cb1;
    public String[] list={"DOLLARS","EUROS ","YEN","POUNDS","RUPEES"};

    public void init() {try {
        SwingUtilities.invokeAndWait(new Runnable(){
                public void run(){
                 Corrected();
                 }
             });
    } catch (InvocationTargetException exc) {
        System.out.println("Error occured due to "+ exc);
        exc.printStackTrace();
    } catch (InterruptedException exc1) {
        System.out.println("Error occured due to "+ exc1);

        exc1.printStackTrace();
    }


 }   




public void Corrected(){



    setLayout(new GridBagLayout());

    JLabel label1 = new JLabel("FROM  :");
    label1.setFont(new Font("Serif", Font.BOLD, 15));

    JComboBox cb = new JComboBox();


    cb= new JComboBox(list);
    cb.getSelectedIndex();

    GridBagConstraints gbc = new GridBagConstraints();
    gbc.gridx = 0;
    gbc.gridy = 0;
    add(label1, gbc);
    gbc.fill = GridBagConstraints.HORIZONTAL;
    gbc.gridx++;
    add(cb, gbc);

    JLabel label2 = new JLabel("TO :");
    label2.setFont(new Font("Serif", Font.BOLD, 15));
    JComboBox cb1 = new JComboBox();
    cb1=new JComboBox(list);
    cb1.getSelectedIndex();

    gbc.gridx = 0;
    gbc.gridy++;
    gbc.fill = GridBagConstraints.NONE;
    add(label2, gbc);
    gbc.fill = GridBagConstraints.HORIZONTAL;
    gbc.gridx++;
    add(cb1, gbc);

    JLabel label3 = new JLabel("\n\nENTER THE AMOUNT  :");
    label3.setFont(new Font("Serif", Font.BOLD, 15));
    label3.setHorizontalAlignment(SwingConstants.CENTER);
    label3.setVerticalAlignment(SwingConstants.CENTER);

    gbc.gridx = 0;
    gbc.gridy++;
    add(label3, gbc);
    JTextField tf1 = new JTextField(15);
    gbc.gridx++;
    add(tf1, gbc);

    JLabel label4 = new JLabel("CONVERTED AMOUNT :");
    label4.setFont(new Font("Serif", Font.BOLD, 15));
    label4.setDisplayedMnemonic(KeyEvent.VK_O);

    gbc.gridx = 0;
    gbc.gridy++;
    add(label4, gbc);
    JTextField tf2 = new JTextField(15);
    gbc.gridx++;
    add(tf2, gbc);

    JPanel buttons = new JPanel();

    JButton button1 = new JButton("CONVERT");
    button1.setFont(new Font("Serif", Font.BOLD, 15));
    button1.setMnemonic(KeyEvent.VK_K);
    buttons.add(button1);

    JButton button2 = new JButton("CLEAR ");
    button2.setFont(new Font("Serif", Font.BOLD, 15));
    button2.setMnemonic(KeyEvent.VK_C);
    buttons.add(button2);

    gbc.gridx = 0;
    gbc.gridy++;
    gbc.gridwidth = GridBagConstraints.REMAINDER;

    add(buttons, gbc);

    thehandler handler= new thehandler();

     cb.addActionListener(handler);
     cb1.addActionListener((ActionListener) handler);    
     button1.addActionListener((ActionListener) handler);    
     button2.addActionListener((ActionListener) handler);    
     tf1.addActionListener((ActionListener) handler);    
     tf2.addActionListener((ActionListener) handler);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//pack();
 setSize(450,250);
setVisible(true);

}


public class thehandler implements ActionListener{


    public void actionPerformed(ActionEvent e) {
        double a=0,b=0; 
        a=Double.valueOf(tf1.getText());
        {
            if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==1)
                b=a*0.89;
            if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==2)
                b=a*124.75;
            if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==3)
                b=a*0.65;
            if(cb.getSelectedIndex()==0 && cb1.getSelectedIndex()==4)
                b=a*64.08;
            if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==0)
                b=a*1.13;
            if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==2)
                b=a*140.49;
            if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==3)
                b=a*0.74;
            if(cb.getSelectedIndex()==1 && cb1.getSelectedIndex()==4)
                b=a*71.34;
            if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==0)
                b=a*0.0080;
            if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==1)
                b=a*0.0071;
            if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==3)
                b=a*0.0052;
            if(cb.getSelectedIndex()==2 && cb1.getSelectedIndex()==4)
                b=a*0.51;
            if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==0)
                b=a*1.53;
            if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==1)
                b=a*1.36;
            if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==2)
                b=a*191.26;
            if(cb.getSelectedIndex()==3 && cb1.getSelectedIndex()==4)
                b=a*97.88;
            if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==0)
                b=a*0.0156;
            if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==1)
                b=a*0.014;
            if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==2)
                b=a*1.9607;
            if(cb.getSelectedIndex()==4 && cb1.getSelectedIndex()==3)
                b=a*0.0108;
            tf2.setText(String.valueOf(b));

        }

        if(e.getSource()==button2){
            tf1.setText("0000");
            tf2.setText("0000");
                        }

    }

}

}

Answer 1

首先看一下如何使用BorderLayout来了解其工作原理。

BorderLayout只能在其中放置五个组件，即NORTH ， SOUTH ， EAST ， WEST和CENTRE

默认情况下，如果没有其他指定，组件将放置在CENTRE位置。 这意味着实际上仅布置了最后添加的组件。

JLabel#setHorizontal/VerticalAlignment将在标签大小较大时对齐标签的内容，但是对于FlowLayout ，它将使用标签内容的首选大小来决定如何最佳布局，因此通常没有多余的空间

相反，您可以使用GridBagLayout ，它是可用的更复杂但灵活的布局管理器之一。

setLayout(new GridBagLayout());

JLabel label1 = new JLabel("FROM  :");
label1.setFont(new Font("Serif", Font.BOLD, 15));

JComboBox cb = new JComboBox();

GridBagConstraints gbc = new GridBagConstraints();
gbc.gridx = 0;
gbc.gridy = 0;
add(label1, gbc);
gbc.fill = GridBagConstraints.HORIZONTAL;
gbc.gridx++;
add(cb, gbc);

JLabel label2 = new JLabel("TO :");
label2.setFont(new Font("Serif", Font.BOLD, 15));
JComboBox cb1 = new JComboBox();

gbc.gridx = 0;
gbc.gridy++;
gbc.fill = GridBagConstraints.NONE;
add(label2, gbc);
gbc.fill = GridBagConstraints.HORIZONTAL;
gbc.gridx++;
add(cb1, gbc);

JLabel label3 = new JLabel("\n\nENTER THE AMOUNT  :");
label3.setFont(new Font("Serif", Font.BOLD, 15));
label3.setHorizontalAlignment(SwingConstants.CENTER);
label3.setVerticalAlignment(SwingConstants.CENTER);

gbc.gridx = 0;
gbc.gridy++;
add(label3, gbc);
JTextField tf1 = new JTextField(15);
gbc.gridx++;
add(tf1, gbc);

JLabel label4 = new JLabel("CONVERTED AMOUNT :");
label4.setFont(new Font("Serif", Font.BOLD, 15));
label4.setDisplayedMnemonic(KeyEvent.VK_O);

gbc.gridx = 0;
gbc.gridy++;
add(label4, gbc);
JTextField tf2 = new JTextField(15);
gbc.gridx++;
add(tf2, gbc);

JPanel buttons = new JPanel();

JButton button1 = new JButton("CONVERT");
button1.setFont(new Font("Serif", Font.BOLD, 15));
button1.setMnemonic(KeyEvent.VK_K);
buttons.add(button1);

JButton button2 = new JButton("CLEAR ");
button2.setFont(new Font("Serif", Font.BOLD, 15));
button2.setMnemonic(KeyEvent.VK_C);
buttons.add(button2);

gbc.gridx = 0;
gbc.gridy++;
gbc.gridwidth = GridBagConstraints.REMAINDER;
add(buttons, gbc);

有时，您甚至需要结合使用第二个JPanel ，使用FlowLayout作为按钮的布局（在此完成），因为这会产生使按钮居中的理想结果

有关更多详细信息，请参见如何使用GridBagLayout 。

Answer 2

组件的位置相对于其所属的布局。

如果您真的想自由设置JLabel和JButton的位置，我建议您将布局设置为null：

setLayout(null);

并通过使用setBounds() 4个参数的setBounds()定位JLabel 。 JLabel尺寸及其坐标。