How to Position a JLabel in the specified Layout?

问题:

I am trying to position my Labels and Button on screen. I found an answer here to set label's Position using: label3.setHorizontalAlignment(SwingConstants.CENTER); label3.setVerticalAlignment(SwingConstants.CENTER); but there has been no effect in my code.

Also, on changing my layout from Flow Layout to Border Layout, only one Jbutton [CLEAR] appears on the Screen. Can anyone help me rectify this?

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");
                        }

    }

}

}

回答1:

Start by taking a look at How to Use BorderLayout to understand how it works.

BorderLayout will only allow five components to positioned within it, NORTH, SOUTH, EAST, WEST and CENTRE

By default, components are placed in the CENTRE position if you don't otherwise specify. This means that only the last component added is actually laid out.

JLabel#setHorizontal/VerticalAlignment will align the contents of the label when the size of the label is larger, but in the case of FlowLayout, it uses the preferred size of the label's content to make decisions about how best to lay it out, so there's generally no extra space

Instead, you could use a GridBagLayout, which a one of the more complicated, but flexible layout managers available.

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);

Sometimes, you even need to combine layouts, which I've done here, using a second JPanel, using a FlowLayout for the buttons, because it produces the desired result of centring the buttons

See How to Use GridBagLayout for more details

回答2:

Components positioning is relative to the layout it belongs to.

If you really want to freely set the position of your JLabel's and JButton's, I advise you to set the layout to null:

setLayout(null);

and position the JLabel by using the setBounds() taking 4 parameters. Dimension of the JLabel and its coordinates.