Painting cells certain colours depending on value within previous row JXTreeTable

Question

I've got a JXTreeTable with a custom cell renderer. I am attempting to get the background colour of a row to change when a field in a row is different from the field in the previous row. Say for example that the row contains "1" as the ID. If the previous row also contained "1", i want this row to be painted the same colour. If the previous was "2", I want this row to be painted the alternative colour. The aim is to group rows with the same ID.

I originally was storing the previously painted colour and using that (along with the value) to determine what colour to paint the current row. However this only worked when fully painting the table from top to bottom. I currently am fetching the previous rows background colour and using that to determine, but if the row is selected or otherwise different, this messes up the colours. Is there a better way to do this?

public Component prepareRenderer(TableCellRenderer renderer, int row, int column) {
    Component c = super.prepareRenderer(renderer, row, column);
    Object node = this.getPathForRow(row).getLastPathComponent();

    if(node instanceof Record && !isCellSelected(row,column)) {
    Object prevNode = null;
    Component prevC = null;
    if(row > 1) {
        prevC = super.prepareRenderer(renderer, row-1, column);
        prevNode = this.getPathForRow(row-1).getLastPathComponent();
    }
        if(row != prevRow) { //paint rows the same colour
            if(getTreeTableModel().getValueAt(node,17) != null) {
                if (prevNode != null) {
                    if(getTreeTableModel().getValueAt(prevNode, 17) == getTreeTableModel().getValueAt(node, 17)) { 
                        c.setBackground(prevC.getBackground()); //if ID is same as previous ID, paint same colour
                        prevColor = prevC.getBackground();
                    }else if(prevC.getBackground().equals(Color.WHITE)) {;
                        c.setBackground(new Color(240,255,255)); //if previous row was white, paint blue
                        prevColor = new Color(240,255,255);
                    }else if(prevC.getBackground().equals(new Color(240,255,255))) {                            
                        c.setBackground(Color.WHITE); //if previous row blue, paint white
                        prevColor = Color.WHITE;
                    }
                } else {
                    c.setBackground(Color.WHITE); //previous node is null 
                    prevColor = Color.WHITE;
                }
            }
        } else {
            c.setBackground(prevColor);
        }
    }
    prevRow = row;
    return c;
}

Answer 1

If you are not changing your data much you could just pre-determine the colors for each id and look them up before setting the background each time.

Answer 2

I am attempting to get the background colour of a row to change when a field in a row is different from the field in the previous row

If you are attempting to do background rendering based on the data in a row then I would use the Table Row Rendering approach.