Thread: Hello everyone! I need help with JTable

Hi everyone i'm a newby with java

I have a JTable where birdwatchers can put in the column "[Bird Seen] ,how much birds they have seen.
And if you push the >SEND> button this account of [Birds Seen] must be accumelated on the [Birds Total] column.
For example if you put 3 in column [Birds Seen] then also 3 must appear in the column [Birds Total] after you push the >SEND> button.
But if you put for the second time lets say 4 in column [Bird Seen] then 7 must appear on the column [Birds Total]. Because you saw the first time 3 birds and the second time 4 birds so 3+4=7.

I hope you understand what i mean, if not don't bother to ask.
Here is a picture of how my table looks like, And the java code.

every help is welcom!

package Tabel01;
 
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.ScrollPaneConstants;
import javax.swing.table.AbstractTableModel;
 
 
public class TableDemo extends JPanel implements ActionListener   {
 
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
 
    public  JButton   actieknop;
    public  JFrame    venster;
    public  JTable    table;
    public  JPanel    panel1, panel2;
 
 
    public TableDemo() {
 
        //Create and set up the window.
         venster = new JFrame("BirdCount");
 
 
        //make panels
         panel1 = new JPanel();
         panel2 = new JPanel();
         //Create and set up the content pane.
          venster.add(panel1, BorderLayout.CENTER);
         venster.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         venster.setSize(450,300);
 
         //make table
            table = new JTable(new MyTableModel());
            panel1.add(table);
            JScrollPane scroller1 = new JScrollPane(table);
            scroller1.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
            scroller1.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
            panel1.add(scroller1);
 
 
        table.setPreferredScrollableViewportSize(new Dimension(250, 150));
 
 
        //Make button
         actieknop = new JButton(">SEND>");
         actieknop.addActionListener(this);
         panel2.add(actieknop);
         //panel2.add(actieknop2);
         venster.add(panel2, BorderLayout.EAST);
 
 
         //Display the window.
         venster.setVisible(true);
}
 
    class MyTableModel extends AbstractTableModel {
 
        /**
         * 
         */
        private static final long serialVersionUID = 1L;
 
        String[] columnNames = { "Bird",
                                           "Birds seen",
                                               "Birds Total",
                                                       };
 
         Object[][] data = {
               {"falck", "",
                   "", new Integer(0) , new Integer(0)},
                   {"pigeon", "",
                       "", new Integer(0), new Integer(0)},
                       };
 
         public int getColumnCount() {
             return columnNames.length;
         }
 
         public int getRowCount() {
             return data.length;
         }
 
         public String getColumnName(int col) {
             return columnNames[col];
         }
 
         public Object getValueAt(int row, int col) {
             return data[row][col];
         }
 
         public boolean isCellEditable(int row, int col) {
             //Note that the data/cell address is constant,
             //no matter where the cell appears onscreen.
             if (col == 0 || col == 4){
                 return false;
             }
           else {
                 return true;
             }
         }
    }
 
 
     public static void main(String[] args) {
     new TableDemo();
 
     }
 
@Override
    public void actionPerformed(ActionEvent arg0) {
        // TODO Auto-generated method stub
 
    }
         }

Originally Posted by hektor

Hi thank you for your quick reply.
i'm not so good at writing english maybe thats why you don't understand me.:confused


The problem is not that something is happening i don't want to happen.
But i have explained what i would like to happen if i push the >SEND> Button.
I hoped someone could tell me how i could make work the >SEND> buton, like i explained in the introduction.
Because i don't know how i must pass a number from one column to another in a JTable.

i think i should do it with public void actionPerformed(ActionEvent arg0) { }, But i'm really a beginner with java so i hoped someone can give me a hint to get started.
Or should i put an if/ else statement in actionPerformed.

Ok, I understand what you are saying.

This is actually quite simple. You know the row directly above the row you are adding to has the total. And you know how much you want to add to that total to get the value you are inserting into the current row.

There are two ways of doing this:
Method 1:
So, the first thing you need to do is check which row has been added to. Provided the user has not changed the row they have added to, there is no problem. Otherwise, method 2 will be better. This method ALSO assumes the user hasn't changed any previous values. So, to do this, you first need to check the if you are on the first row. This can be done with the statement:

if(table.getSelectedRow()==0)
{...}
else
{...}

If the selected row is the first row, then you want its column value to be equal to the value inputted on the left. Otherwise, you want the value to be equal to the value directly above + the value directly to the left. You can get these value using the method:

int value = Integer.parseInt(table.getValueAt(row,column))

Where: row is the row of the value you are getting and column is the column of the value you are getting. Keep in mind that you want to parse what you get here into an int. This is because the getValueAt(int,int) method returns an Object, but we need to add with ints. As a result, we have to parse the Object into an int. You know that if you are trying to get the value of the row previous to the current selected one, you can say:

int row = table.getSelectedRow()-1;

and if you are trying to get the column of value to the left of you, then column would be equal to 1. Although it is Column 2, it is Column Index 1.
Lastly, you need to set the value of the cell using the method:

table.setValueAt(value,row,column);

Where: value is the value you have after you have added together the cell directly above you and the cell to the left of you. row is the the current row you are adding to. And column is the equal to 2.

Method 2:
This method is probably the better option, as it is more dynamic. Here we use a LOOP instead of an IF statement. For this, we will go through each row and add the values each time the button is pressed. Although this may mean we are reevaluating values that will not change, it is a better option if those values could change.
What we can do is Loop through every row and add up the values in the column directly to the left of it. To do this, we need to create a FOR LOOP like this:

for(int i=0;i<table.getRowCount();i++)
{...}

This FOR LOOP does not require us to check if there is only 1 row, as that is handled in the by the condition. Now, we want another FOR LOOP inside that loops through all the rows as well. To declare that, our total looping would look like this:

for(int i=0;i<table.getRowCount();i++)
{
	for(int n=0;n<=i;n++)
	{...}
}

The reason we do this is because we want to add up all the values on the cell on the left. But we also want to increment down the JTable rows. Keep in mind that our condition in our nested FOR LOOP goes until it is EQUAL TO OR LESS THAN our i variable. This is because we want to add up to, and including the row we are accessing. Now that we have our nested FOR LOOPs, we need to get each value and add them all together. This requires we make our total variable outside of our inner FOR LOOP and that we use the getValueAt(int,int) method that we discussed earlier. So, that would look like this:

for(int i=0;i<table.getRowCount();i++)
{
	int total = 0;
	for(int n=0;n<=i;n++)
	{
		total += Integer.parseInt(table.getValueAt(n,1));
	}
}

What this is saying is that we are getting the value of Column 2 on Row n and adding it to our total. The int parsing is explained on Method 1. The last thing we need to do is set the value at the Column 3 on Row i to be equal to our total variable. In order to do that, we need to use the setValueAt(Object,int,int) method which was explained in Method 1. That would look like this:

for(int i=0;i<table.getRowCount();i++)
{
	int total = 0;
	for(int n=0;n<=i;n++)
	{
		total += Integer.parseInt(table.getValueAt(n,1));
	}
	table.setValueAt(total,i,2);
}

I believe that is it. Tell me if you have any questions. I want to make sure you understand the code.

eh, do this instead:

total += Integer.parseInt(table.getValueAt(n,1).toString());

I think you can alternatively do:

total += ((Integer)table.getValueAt(n,1)).intValue());

I can't remember exactly how to turn an Object into a primitive type. Both of those should do it however.

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