FlowLayout使标签居中？

Question

我正在用FlowLayout制作一个表格。表单的GUI如下所示：

Name: <textField>
    Age: <textfiedl>
    Gender: Male[] Female[]
Email: <textField>

对于性别，选项是单选按钮。如你所见，年龄和性别的标签应该居中。如何使用FlowLayout完成此操作

Answer 1

如果整个表单是使用BoxLayout创建的，其中一个是面向BoxLayout.PAGE_AXIS的，那么如果表单的每一条“线”都是一个使用FlowLayout的JPanel，那么默认情况下它们持有的组件应该居中，因为JPanel使用new FlowLayout(FlowLayout.CENTER, 5, 5)作为其默认布局(实际上它使用new FlowLayout()，但此构造函数的默认值如上所述--居中方向，水平和垂直间距为5)。

另一种选择是使用填充，并为每行上的组件更改约束的GridBagLayout和weighty属性。

例如：

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import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.*;

public class LayoutExample extends JPanel {
    private static final long serialVersionUID = 1L;
    private JTextField ageField = new JTextField(10);
    private JTextField emailField = new JTextField(10);
    private ButtonGroup sexBtnGroup = new ButtonGroup();
    private JRadioButton maleBtn = new JRadioButton("Male");
    private JRadioButton femaleBtn = new JRadioButton("Female");

    public LayoutExample() {
        JPanel agePanel = new JPanel(new FlowLayout(FlowLayout.LEADING, 5, 5));
        agePanel.add(new JLabel("Age:"));
        agePanel.add(ageField);

        sexBtnGroup.add(maleBtn);
        sexBtnGroup.add(femaleBtn);;
        JPanel sexSelectionPanel = new JPanel();
        sexSelectionPanel.add(new JLabel("Select Sex:"));
        sexSelectionPanel.add(maleBtn);
        sexSelectionPanel.add(femaleBtn);

        JPanel emailPanel = new JPanel(new FlowLayout(FlowLayout.LEADING, 5, 5));
        emailPanel.add(new JLabel("Email:"));
        emailPanel.add(emailField);

        int gap = 10;
        setBorder(BorderFactory.createEmptyBorder(gap, gap, gap, gap));
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
        add(agePanel);
        add(Box.createVerticalStrut(5));
        add(sexSelectionPanel);
        add(Box.createVerticalStrut(5));
        add(emailPanel);        
    }

    // make it stretch horizontally to see placement
    @Override
    public Dimension getPreferredSize() {
        Dimension superSize = super.getPreferredSize();
        int width = (3 * superSize.width) / 2;
        int height = superSize.height;
        return new Dimension(width, height);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

    private static void createAndShowGui() {
        LayoutExample mainPanel = new LayoutExample();
        JFrame frame = new JFrame("LayoutExample");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
}

示例2使用GridBagLayout：

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import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.Insets;
import javax.swing.*;

public class LayoutExample2 extends JPanel {
    private static final long serialVersionUID = 1L;
    private JTextField ageField = new JTextField(10);
    private JTextField emailField = new JTextField(10);
    private ButtonGroup sexBtnGroup = new ButtonGroup();
    private JRadioButton maleBtn = new JRadioButton("Male");
    private JRadioButton femaleBtn = new JRadioButton("Female");

    public LayoutExample2() {

        JPanel sexSelectPanel = new JPanel(new GridLayout(1, 0, 5, 5));
        sexBtnGroup.add(maleBtn);
        sexSelectPanel.add(maleBtn);
        sexBtnGroup.add(femaleBtn);
        sexSelectPanel.add(femaleBtn);

        int gap = 10;
        setBorder(BorderFactory.createEmptyBorder(gap, gap, gap, gap));
        setLayout(new GridBagLayout());

        add(new JLabel("Age:"), createGbc(0, 0));
        add(ageField, createGbc(1, 0));

        add(new JLabel("Sex:"), createGbc(0, 1));
        add(sexSelectPanel, createGbc(1, 1));

        add(new JLabel("Email:"), createGbc(0, 2));
        add(emailField, createGbc(1, 2));
    }

    private static GridBagConstraints createGbc(int x, int y) {
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = x;
        gbc.gridy = y;
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        int ins = 4;
        gbc.insets = new Insets(ins, ins, ins, ins);
        gbc.fill = GridBagConstraints.HORIZONTAL;
        return gbc;
    }

    // make it stretch horizontally to see placement
    @Override
    public Dimension getPreferredSize() {
        Dimension superSize = super.getPreferredSize();
        int width = (4 * superSize.width) / 3;
        int height = superSize.height;
        return new Dimension(width, height);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

    private static void createAndShowGui() {
        LayoutExample2 mainPanel = new LayoutExample2();
        JFrame frame = new JFrame("LayoutExample");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
}

Answer 2

这是一种方法(可能有很多种方法)。标题边框中的布局详细信息。

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注意:对于任何与选择数字有关的事情，最好为用户提供一个微调控件。