Question

I’m trying to implement a custom TableRenderer as described in this tutorial.
I’d like to have the renderer line-wrap each text that is to long for the given cell.
The idea is, to use a TextArea as renderer, as it supports line wrapping. However, the following code does not behave as expected:

public class LineWrapCellRenderer  extends JTextArea implements TableCellRenderer {

    @Override
    public Component getTableCellRendererComponent(
            JTable table,
            Object value,
            boolean isSelected,
            boolean hasFocus,
            int row,
            int column) {
        this.setText((String)value);
        this.setWrapStyleWord(true);            
        this.setLineWrap(true);         
        return this;
    }

}

I set this renderer with

table.setDefaultRenderer(String.class, new LineWrapCellRenderer());

But the cell entries stay unwrapped.
If I add this.setBackground(Color.YELLOW) to the getTableCellRendererComponent() method,
all cells are yellow as expected, but not wrapped.

Any ideas?

UPDATE: As Michael Borgwardt stated in the comments, the problem is not the line wrap, but the row height: JTables rows are fixed size, so if a cell is getting higher (cause the text is now multi-lined), we have to increase the row height.
But how much? I will check if this is worth another SO-question. If not, I will add this solution here.

Update2: The following code will determine the row height (if placed in getTableCellRendererComponent()):

int fontHeight = this.getFontMetrics(this.getFont()).getHeight();
int textLength = this.getText().length();
int lines = textLength / this.getColumns() +1;//+1, cause we need at least 1 row.           
int height = fontHeight * lines;            
table.setRowHeight(row, height);

Answer 1

The problem is that the height of rows in JTable is fixed, so it’s not just a matter of having a renderer that wraps; I’m not sure why it doesn’t, but if it did, the wrapped text would be cropped – or maybe that’s exactly what you’re seeing. To adjust row heights, you need to set them individually.

Heres’ some code for that:

int rows = 10;
int cols = 5;
JTable table = new JTable(rows, cols);

// Set the 1st row to 60 pixels high
table.setRowHeight(0, 60);

// Set the height of all rows to 32 pixels high,
// regardless if any heights were assigned to particular rows
table.setRowHeight(32);
// the height of the 1st row is set to 32 pixels high

// Returns the preferred height of a row.
// The result is equal to the tallest cell in the row.
public int getPreferredRowHeight(JTable table, int rowIndex, int margin) {
    // Get the current default height for all rows
    int height = table.getRowHeight();

    // Determine highest cell in the row
    for (int c=0; c<table.getColumnCount(); c++) {
        TableCellRenderer renderer = table.getCellRenderer(rowIndex, c);
        Component comp = table.prepareRenderer(renderer, rowIndex, c);
        int h = comp.getPreferredSize().height + 2*margin;
        height = Math.max(height, h);
    }
    return height;
}

// The height of each row is set to the preferred height of the
// tallest cell in that row.
public void packRows(JTable table, int margin) {
    packRows(table, 0, table.getRowCount(), margin);
}

// For each row >= start and < end, the height of a
// row is set to the preferred height of the tallest cell
// in that row.
public void packRows(JTable table, int start, int end, int margin) {
    for (int r=0; r<table.getRowCount(); r++) {
        // Get the preferred height
        int h = getPreferredRowHeight(table, r, margin);

        // Now set the row height using the preferred height
        if (table.getRowHeight(r) != h) {
            table.setRowHeight(r, h);
        }
    }
}