How to swap value of cell in jtable by drag and drop

Question

I would like to swap the data of my table from one table to another IN THE SAME COLUMN (Note: I have only two columns).

My problem is I cannot swap the value. Also,

Answer 1

Drag and drop is not a simple process, it's quite complex and involved. With this complexity comes flexibility.

Swapping values in this way isn't the same as "moving" per se. When moving something, you take it from the source and place it in the target, here we are swapping values between the source and target, this means we need more information than is generally available via the API.

First of all, you're going to need a custom class to hold the data to be exported, because we're moving data, this is going to require some additional information, in particular, the source component...

The following is just a simple wrapper. We could export the JTable entirely, but I wanted to demonstrate a basic concept of drag-n-drop...

import javax.swing.JTable;

public class CellData {
    private JTable table;

    public CellData(JTable table) {
        this.table = table;
    }

    public int getColumn() {
        return table.getSelectedColumn();
    }

    public String getValue() {
        int row = table.getSelectedRow();
        int col = table.getSelectedColumn();
        return (String) table.getValueAt(row, col);
    }

    public JTable getTable() {
        return table;
    }

}

Next, we need a custom Transferable to manage our data...

import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;

public class CellDataTransferable implements Transferable {

    public static final DataFlavor CELL_DATA_FLAVOR = createConstant(CellData.class, "application/x-java-celldata");
    private CellData cellData;

    public CellDataTransferable(CellData cellData) {
        this.cellData = cellData;
    }

    @Override
    public DataFlavor[] getTransferDataFlavors() {
        return new DataFlavor[]{CELL_DATA_FLAVOR};
    }

    @Override
    public boolean isDataFlavorSupported(DataFlavor flavor) {
        boolean supported = false;
        for (DataFlavor available : getTransferDataFlavors()) {
            if (available.equals(flavor)) {
                supported = true;
            }
        }
        return supported;
    }

    @Override
    public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
        return cellData;
    }

    static protected DataFlavor createConstant(Class clazz, String name) {
        try {
            return new DataFlavor(clazz, name);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

}

And finally, the TransferHandler....

public class TransferHelper extends TransferHandler {

    private static final long serialVersionUID = 1L;

    public TransferHelper() {
    }

    @Override
    public int getSourceActions(JComponent c) {
        return MOVE;
    }

    @Override
    protected Transferable createTransferable(JComponent source) {
        // Create the transferable
        // Because I'm hacking a little, I've included the source table...
        JTable table = (JTable) source;
        return new CellDataTransferable(new CellData(table));
    }

    @Override
    protected void exportDone(JComponent source, Transferable data, int action) {
    }

    @Override
    public boolean canImport(TransferSupport support) {
        // Reject the import by default...
        boolean canImport = false;
        // Can only import into another JTable
        Component comp = support.getComponent();
        if (comp instanceof JTable) {
            JTable table = (JTable) comp;
            // Need the location where the drop might occur
            DropLocation dl = support.getDropLocation();
            Point dp = dl.getDropPoint();
            // Get the column at the drop point
            int dragColumn = table.columnAtPoint(dp);
            try {
                // Get the Transferable, we need to check
                // the constraints
                Transferable t = support.getTransferable();
                CellData cd = (CellData) t.getTransferData(CellDataTransferable.CELL_DATA_FLAVOR);
                // Make sure we're not dropping onto ourselves...
                if (cd.getTable() != table) {
                    // Do the columns match...?
                    if (dragColumn == cd.getColumn()) {
                        canImport = true;
                    }
                }
            } catch (UnsupportedFlavorException | IOException ex) {
                ex.printStackTrace();
            }
        }
        return canImport;
    }

    @Override
    public boolean importData(TransferSupport support) {
        // Import failed for some reason...
        boolean imported = false;
        // Only import into JTables...
        Component comp = support.getComponent();
        if (comp instanceof JTable) {
            JTable target = (JTable) comp;
            // Need to know where we are importing to...
            DropLocation dl = support.getDropLocation();
            Point dp = dl.getDropPoint();
            int dropCol = target.columnAtPoint(dp);
            int dropRow = target.rowAtPoint(dp);
            try {
                // Get the Transferable at the heart of it all
                Transferable t = support.getTransferable();
                CellData cd = (CellData) t.getTransferData(CellDataTransferable.CELL_DATA_FLAVOR);
                if (cd.getTable() != target) {
                    // Make sure the columns match
                    if (dropCol == cd.getColumn()) {
                        // Get the data from the "dropped" table
                        String exportValue = (String) target.getValueAt(dropRow, dropCol);
                        // Get the data from the "dragged" table
                        String importValue = cd.getValue();
                        // This is where we swap the values...
                        // Set the target/dropped tables value
                        target.setValueAt(importValue, dropRow, dropCol);

                        // Set the source/dragged tables values
                        JTable source = cd.getTable();
                        int row = source.getSelectedRow();
                        int col = source.getSelectedColumn();
                        source.setValueAt(exportValue, row, col);

                        imported = true;
                    }
                }
            } catch (UnsupportedFlavorException | IOException ex) {
                ex.printStackTrace();
            }

        }
        return imported;
    }
}

Read the comments :P

And finally, a runnable example...

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.DropMode;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.TransferHandler;
import static javax.swing.TransferHandler.MOVE;
import javax.swing.TransferHandler.TransferSupport;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.table.DefaultTableModel;

public class TableSwap {

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

    public TableSwap() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JTable t1 = createTable(0);
                JTable t2 = createTable(20);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new GridLayout(0, 2));
                frame.add(new JScrollPane(t1));
                frame.add(new JScrollPane(t2));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    protected JTable createTable(int startAt) {

        DefaultTableModel model = new DefaultTableModel(0, 2);
        for (int index = 0; index < 10; index++) {
            model.addRow(new Object[]{"0x" + (index + startAt), "1x" + (index + startAt)});
        }

        JTable table = new JTable(model);
        table.setDragEnabled(true);
        table.setDropMode(DropMode.USE_SELECTION);
        table.setTransferHandler(new TransferHelper());
        table.setRowSelectionAllowed(false);
        table.setCellSelectionEnabled(true);

        return table;
    }

}

Updated to support a single table only

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
import javax.swing.DropMode;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.TransferHandler;
import static javax.swing.TransferHandler.MOVE;
import javax.swing.TransferHandler.TransferSupport;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.table.DefaultTableModel;

public class TableSwap {

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

    public TableSwap() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JTable t1 = createTable(0);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new JScrollPane(t1));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    protected JTable createTable(int startAt) {

        DefaultTableModel model = new DefaultTableModel(0, 2);
        for (int index = 0; index < 10; index++) {
            model.addRow(new Object[]{"0x" + (index + startAt), "1x" + (index + startAt)});
        }

        JTable table = new JTable(model);
        table.setDragEnabled(true);
        table.setDropMode(DropMode.USE_SELECTION);
        table.setTransferHandler(new TransferHelper());
        table.setRowSelectionAllowed(false);
        table.setCellSelectionEnabled(true);

        return table;
    }

    public class CellData {

        private final Object value;
        private final int col;
        private final JTable table;
        private final int row;

        public CellData(JTable source) {
            this.col = source.getSelectedColumn();
            this.row = source.getSelectedRow();
            this.value = source.getValueAt(row, col);
            this.table = source;
        }

        public int getColumn() {
            return col;
        }

        public Object getValue() {
            return value;
        }

        public JTable getTable() {
            return table;
        }

        public boolean swapValuesWith(int targetRow, int targetCol) {

            boolean swapped = false;

            if (targetCol == col) {

                Object exportValue = table.getValueAt(targetRow, targetCol);
                table.setValueAt(value, targetRow, targetCol);
                table.setValueAt(exportValue, row, col);
                swapped = true;

            }

            return swapped;

        }

    }

    public static final DataFlavor CELL_DATA_FLAVOR = createConstant(CellData.class, "application/x-java-celldata");

    public class CellDataTransferable implements Transferable {

        private CellData cellData;

        public CellDataTransferable(CellData cellData) {
            this.cellData = cellData;
        }

        @Override
        public DataFlavor[] getTransferDataFlavors() {
            return new DataFlavor[]{CELL_DATA_FLAVOR};
        }

        @Override
        public boolean isDataFlavorSupported(DataFlavor flavor) {
            boolean supported = false;
            for (DataFlavor available : getTransferDataFlavors()) {
                if (available.equals(flavor)) {
                    supported = true;
                }
            }
            return supported;
        }

        @Override
        public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
            return cellData;
        }

    }

    static protected DataFlavor createConstant(Class clazz, String name) {
        try {
            return new DataFlavor(clazz, name);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    public class TransferHelper extends TransferHandler {

        private static final long serialVersionUID = 1L;

        public TransferHelper() {
        }

        @Override
        public int getSourceActions(JComponent c) {
            return MOVE;
        }

        @Override
        protected Transferable createTransferable(JComponent source) {
            // Create the transferable
            JTable table = (JTable) source;
            int row = table.getSelectedRow();
            int col = table.getSelectedColumn();
            Object value = table.getValueAt(row, col);
            return new CellDataTransferable(new CellData(table));
        }

        @Override
        protected void exportDone(JComponent source, Transferable data, int action) {
        }

        @Override
        public boolean canImport(TransferSupport support) {
            // Reject the import by default...
            boolean canImport = false;
            // Can only import into another JTable
            Component comp = support.getComponent();
            if (comp instanceof JTable) {
                JTable target = (JTable) comp;
                // Need the location where the drop might occur
                DropLocation dl = support.getDropLocation();
                Point dp = dl.getDropPoint();
                // Get the column at the drop point
                int dragColumn = target.columnAtPoint(dp);
                try {
                    // Get the Transferable, we need to check
                    // the constraints
                    Transferable t = support.getTransferable();
                    CellData cd = (CellData) t.getTransferData(CELL_DATA_FLAVOR);
                    // Make sure we're not dropping onto ourselves...
                    if (cd.getTable() == target) {
                        // Do the columns match...?
                        if (dragColumn == cd.getColumn()) {
                            canImport = true;
                        }
                    }
                } catch (UnsupportedFlavorException | IOException ex) {
                    ex.printStackTrace();
                }
            }
            return canImport;
        }

        @Override
        public boolean importData(TransferSupport support) {
            // Import failed for some reason...
            boolean imported = false;
            // Only import into JTables...
            Component comp = support.getComponent();
            if (comp instanceof JTable) {
                JTable target = (JTable) comp;
                // Need to know where we are importing to...
                DropLocation dl = support.getDropLocation();
                Point dp = dl.getDropPoint();
                int dropCol = target.columnAtPoint(dp);
                int dropRow = target.rowAtPoint(dp);
                try {
                    // Get the Transferable at the heart of it all
                    Transferable t = support.getTransferable();
                    CellData cd = (CellData) t.getTransferData(CELL_DATA_FLAVOR);
                    if (cd.getTable() == target) {
                        if (cd.swapValuesWith(dropRow, dropCol)) {
                            imported = true;
                        }
                    }
                } catch (UnsupportedFlavorException | IOException ex) {
                    ex.printStackTrace();
                }

            }
            return imported;
        }
    }

}