JTable sorting

[mtyoung]

in my code, jtable sorting done by TableRowSorter...

is it possible to sort table... and ... let say... last row of table remain at the bottom of table after clicking the table Header(sort the table value of row in asc/desc)

[CodesAway]

You can create a comparator to do the specific sort you want. Then use the tableRowSorter.setComparator method to set the comparator for the specific column.

[mtyoung]

is that possible to keep the last row at the bottom of table, no matter what its value and in the sorting in asc or desc order

so...
how do compare(o1, o2) know the object is in the last row?

[CodesAway]

Well, I had two ideas, and neither seem to really work well. Perhaps I'm not familiar enough with JTable, so I'll state my ideas and hopefully they can give some inspiration.

The first idea was to implement a sort method directly, but exclude the last row. This idea could be extended to exclude any row(s). Since you can modify the table's entries, you should be able to write an external sort method, and then fill the values in. However, I don't have enough swing experience to know how to do this.

The second idea was to create a wrapper for an object (a NoSort class). Then, in the comparator, if the object is the NoSort object, leave the two values in the order they are. This method only works if there's one NoSort object.

For example, if row 1 is sortable, 2 is not, 3 is, and 4 is not. When using a merge sort, first row 1 and row 2 would be sorted. However, since row 2 is not sortable, it remains as is (thus row 1 remains). Similarly, row 3 and 4 remain as is, since row 4 is not sortable. In other words, this order is maintained regardless if the sort is in ascending or descending order. Note that row 1 and row 3 are sortable, and should be sorted (in either ascending or descending order).


The code below demonstrates the "goal" of the second idea, but the implementation is poor. However, I provide it, hoping that you can make use of it.

import java.util.Comparator;

import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableModel;
import javax.swing.table.TableRowSorter;

public class Test
{
	/**
	 * Main method
	 * 
	 * @param args
	 *            (not used)
	 */
	public static void main(String[] args)
	{
		TableModel tableModel = new DefaultTableModel(4, 1);
		TableRowSorter<TableModel> sorter = new TableRowSorter<TableModel>(tableModel);
		final JTable table = new JTable(tableModel);
		table.setRowSorter(sorter);
						
		final Comparator<Object> ascendingColumn0 = new Comparator<Object>() {
			
			@Override
			public int compare(Object o1, Object o2)
			{
				if (o1 instanceof NoSort<?> || o2 instanceof NoSort<?>)
				{
					//maintain order
					return -1;
				}
				
				Integer int1 = (Integer) o1;
				Integer int2 = (Integer) o2;
				
				return int1.compareTo(int2);
			}
		};
		
		final Comparator<Object> decendingColumn0 = new Comparator<Object>() {
			@Override
			public int compare(Object o1, Object o2)
			{
				return ascendingColumn0.compare(o2, o1);
			}
		};
		
		table.setValueAt(1, 0, 0);
		table.setValueAt(3, 1, 0);		
		table.setValueAt(7, 2, 0);
		table.setValueAt(new NoSort<Integer>(21), 3, 0);
		
		System.out.println("Ascending order:");
		sorter.setComparator(0, ascendingColumn0);
		sorter.toggleSortOrder(0);
		output(table);
		
		System.out.println("Descending order:");
		sorter.setComparator(0, decendingColumn0);
		sorter.sort();
		output(table);		
	}
	
	private static void output(JTable table)
	{
		for (int i = 0; i < table.getRowCount(); i++)
		{
			System.out.println(table.getValueAt(i, 0));
		}
	}
	
	/**
	 * Wrapper class for an object you don't want sorted
	 */
	static class NoSort<T>
	{
		T value;
		
		NoSort(T value)
		{
			this.value = value;
		}
		
		public T getValue()
		{
			return value;
		}
		
		public void setValue(T value)
		{
			this.value = value;
		}
		
		@Override
		public String toString()
		{
			return value.toString();
		}
	}
}

[mtyoung]

thx very much CodesAway.
i will try both methods

[mtyoung]

i change the NoSort to implements interface Comparable, with method compareTo(T)
add instance variable sort, which indicate the NoSort object should sort or not

	public int compareTo(T o)
	{
		NoSort<?> tmpObj = (NoSort<?>)o;
		if (this.sort == false || tmpObj.sort == false)
		{
			//maintain order
			return 0;
		}
		else
		{
			return ((Comparable) this.value).compareTo(tmpObj.value);
		}
	}

i also override getColumnClass, getValueAt, setValueAt of DefaultTableModel

now the table support NoSort to Number and String


thx very much CodesAway.

[CodesAway]

So you got it working? Awesome! Can you post the updated code (I'm curious how it looks)? Is it able to handle multiple non-sorting values, or just one?

From your code, I see that 0 (and not -1) is what I should have used to maintain order. Changing that single line allows using sorter.toggleSortOrder(0); to toggle between ascending and descending order. Also, only one comparator is required (no need to switch comparators when changing the sort order). I'm REALLY glad I posted my idea, I learned something really useful! I completely forgot that since the sort is stable, returning 0 would keep the values in order. So, thank you very much for that!