使用Flow Layout（Homework）初始化多个JPanel

Question

我正在尝试使用FlowLayout创建一个内部插入两个JPanel的JFrame。我在一个单独的文件中初始化了框架，但这就是我所谓的

public class FlowInFlow extends JFrame
{
public FlowInFlow() {

    setLayout(new FlowLayout());

    JPanel panel1 = new JPanel(new FlowLayout(FlowLayout.LEFT));
    panel1.setBackground(Color.RED);

    JPanel panel2 = new JPanel(new FlowLayout(FlowLayout.RIGHT));
    panel2.setBackground(Color.BLUE);   

}
}

编辑：当我运行这个时，我只得到一个空白框，当我需要两个框并排

时

Answer 1

正如我已经说过的，JPanel的默认首选大小是0x0 ...

这意味着当您将其添加到FlowLayout等布局时，使用首选尺寸，它会显示......好吧......它不会

public class TestFlowLayout {

    public static void main(String[] args) {
        new TestFlowLayout();
    }

    public TestFlowLayout() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JPanel master = new JPanel(new FlowLayout(FlowLayout.LEFT));
                JPanel left = new JPanel();
                left.setBackground(Color.RED);
                left.add(new JLabel("Lefty"));

                JPanel right = new JPanel();
                right.setBackground(Color.BLUE);
                right.add(new JLabel("Righty"));

                master.add(left);
                master.add(right);

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(master);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

Answer 2

除了改变外部布局的建议外，这些组件从未被添加到任何东西（因此永远不可见）。

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

public class FlowInGrid extends JFrame  {

    public FlowInGrid() {

        setLayout(new GridLayout(1,0));

        JPanel panel1 = new JPanel(new FlowLayout(FlowLayout.LEFT));
        panel1.setBackground(Color.RED);
        // ADD Them to something!
        add(panel1);

        JPanel panel2 = new JPanel(new FlowLayout(FlowLayout.RIGHT));
        panel2.setBackground(Color.BLUE);   
        // ADD Them to something!
        add(panel2);
    }

    public static void main(String[] args) throws Exception {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                JFrame f = new FlowInGrid();
                f.setSize(300,100);
                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}