Set Column Width of JTable by Percentage

Question

I need to assign a fixed width to a few columns of a JTable and then an equal width to all the other columns.

Suppose a JTable has 5 column

Answer 1

It think it would be easier to use (and re-use) relative component resizing if we encapsulate it in an own class. Since I also was confronted with the same issue, I would like to post my code here.

From a client perspective I would like to do something like this

TableColumnModel columnModel = jTable.getColumnModel();

TableColumn firstColumn = columnModel.getColumn(0);
TableColumn secondColumn = columnModel.getColumn(1);

ComponentResize columnResize = new TableColumnResize();
RelativeWidthResizer relativeWidthResizer = new RelativeWidthResizer(columnResize);

relativeWidthResizer.setRelativeWidth(firstColumn, 0.8);
relativeWidthResizer.setRelativeWidth(secondColumn, 0.2);

jTable.addComponentListener(relativeWidthResizer);

So I first defined the ComponentResize interface and implement a TableColumnResize

public interface ComponentResize {
    public void setWidth(T component, int width);
}

public class TableColumnResize implements ComponentResize {

    public void setWidth(TableColumn component, int width) {
        component.setPreferredWidth(width);
    }
}

The ComponentResize interface decouples the way a component's size is set from the concrete APIs. E.g. a TableColumn's width can be set via setPreferredWidth(int) while a JComponent's size can be set by setPreferredWidth(Dimension)

Than I implemented the RelativeWidthResizer that encapsulates the relative width calculation logic.

public class RelativeWidthResizer extends ComponentAdapter {

    private Map relativeWidths = new HashMap();
    private ComponentResize componentResize;

    public RelativeWidthResizer(ComponentResize componentResize) {
        this.componentResize = componentResize;
    }

    public void setRelativeWidth(T component, double relativeWidth) {
        if (relativeWidth < 0.0) {
            throw new IllegalArgumentException(
                    "Relative width must be greater or equal to 0.0");
        }

        if (relativeWidth > 1.0) {
            throw new IllegalArgumentException(
                    "Relative width must be less or equal to 1.0");
        }

        double totalRelativeWidth = 0.0;
        for (Double relativeComponentWidth : relativeWidths.values()) {
            totalRelativeWidth += relativeComponentWidth.doubleValue();
        }

        double availableRelativeWidth = 1.0d - (totalRelativeWidth + relativeWidth);

        boolean totalPercentageExceeded = availableRelativeWidth < 0;
        if (totalPercentageExceeded) {
            double remainingRelativeWidth = 1.0d - totalRelativeWidth;
            String message = MessageFormat.format(
                    "Can't set component's relative width to {0}."
                            + " {1} relative width remaining", relativeWidth,
                    remainingRelativeWidth);
            throw new IllegalArgumentException(message);
        }

        relativeWidths.put(component, relativeWidth);
    }

    @Override
    public void componentResized(ComponentEvent e) {
        Component component = e.getComponent();
        apply(component);
    }

    public void apply(Component baseComponent) {
        Dimension size = baseComponent.getSize();
        int maxWidth = (int) size.getWidth();

        int remaining = maxWidth;

        Set> entrySet = relativeWidths.entrySet();
        Iterator> entrySetIter = entrySet.iterator();

        while (entrySetIter.hasNext()) {
            Entry componentEntry = entrySetIter.next();
            T componentToResize = componentEntry.getKey();
            Double relativeWidth = componentEntry.getValue();

            int width = (int) (maxWidth * relativeWidth.doubleValue());
            remaining -= width;

            boolean lastComponent = !entrySetIter.hasNext();
            if (lastComponent && remaining > 0) {
                width += remaining;
            }
            componentResize.setWidth(componentToResize, width);
        }
    }
}