Main.java

import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.border.CompoundBorder;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;
import java.awt.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDropEvent;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.File;
import java.io.IOException;

/**
 * javadoc here.
 *
 * @author Getaji
 */
public class Main {
    public static void main(String[] args) {
        final JDialog dialog = new JDialog((JFrame) null, "Input");
        dialog.setSize(400, 200);

        final EmptyBorder marginBorder = new EmptyBorder(5, 5, 5, 5);

        final JLabel imageLabel = new JLabel();
        imageLabel.setHorizontalAlignment(JLabel.CENTER);
        final CompoundBorder imageBorder = new CompoundBorder(
                new LineBorder(Color.GRAY),
                marginBorder
        );
        dialog.add(imageLabel, BorderLayout.NORTH);

        final JTextArea area = new JTextArea();
        final int padding = 2;
        area.setBorder(new CompoundBorder(
                marginBorder,
                new CompoundBorder(
                        new LineBorder(Color.GRAY),
                        marginBorder
                )));
        dialog.add(area, BorderLayout.CENTER);
        dialog.setBackground(Color.GRAY);

        final JPanel panel = new JPanel();
        panel.setBorder(marginBorder);
        panel.setLayout(new FlowLayout(FlowLayout.RIGHT));
        final String _140 = "/140";
        final JLabel label = new JLabel(0 + _140);
        final JButton button = new JButton("TWEET");
        panel.add(label);
        panel.add(button);
        dialog.add(panel, BorderLayout.SOUTH);

        area.addKeyListener(new KeyListener() {
            @Override
            public void keyTyped(KeyEvent e) {
                label.setText(String.valueOf(area.getText().length()) + _140);
            }

            @Override public void keyPressed(KeyEvent e) {}
            @Override public void keyReleased(KeyEvent e) {}
        });
        area.setDropTarget(new DropTarget() {
            @Override public void drop(DropTargetDropEvent e) {
                try {
                    Transferable transfer = e.getTransferable();
                    // ファイルリストの転送を受け付ける
                    if (transfer.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
                        // copyとmoveを受け付ける
                        e.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE);
                        // ドラッグ＆ドロップされたファイルのリストを取得
                        java.util.List<File> fileList =
                                (java.util.List<File>) transfer.getTransferData(
                                        DataFlavor.javaFileListFlavor);
                        if (0 < fileList.size() && fileList.get(0).isFile()) {
                            System.out.println(fileList.get(0).getAbsolutePath());
                            ImageIcon imageIcon = new ImageIcon(
                                    ImageIO.read(fileList.get(0))
                            );
                            imageLabel.setIcon(imageIcon);
                            imageLabel.setPreferredSize(new Dimension(Integer.MAX_VALUE, 50));
                            if (dialog.getHeight() <= 200) {
                                dialog.setSize(dialog.getWidth(), 250);
                            }
                        }
                    }
                } catch (UnsupportedFlavorException e1) {
                    e1.printStackTrace();
                } catch (IOException e2) {
                    e2.printStackTrace();
                }
            }
        });

        dialog.setVisible(true);
    }
}