How to make Editable JTable in Java Swing

int rowCount = model.getRowCount();
int columnCount = model.getColumnCount();
for(int i=0; i<rowCount; i++) {
  for(int j=0; j<columnCount; j+) {
    Object cellValue = model.getValueAt(i,j);
    //now display this value graphically.
  }
}

Note that, the row numbers and column numbers begin indexing at 0 and hence we start from 0.

The actual code written by the Swing API developers would be much more complex. But, this should give an idea of what actually happens behind the scenes. And that in turn, helps us to understand how and what to write in a TableModel implementation.

Remember that TableModel is an interface and we have to provide or implementation. Fortunately, Swing provides a class named AbstractTableModel which provides a default implementation for many methods in this interface. So, we can simply extend this class and implement those methods which we need to.

Before doing that, let us first define our POJO model. This class is simply a value bean which represents the actual entity:

package net.codejava.model;

public class Employee
{
    private int id;
    private String name;
    private double hourlyRate;
    private boolean partTime;

    public Employee(int id, String name, double hourlyRate, boolean partTime)
    {
        this.id = id;
        this.name = name;
        this.hourlyRate = hourlyRate;
        this.partTime = partTime;
    }

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public double getHourlyRate()
    {
        return hourlyRate;
    }

    public void setHourlyRate(double hourlyRate)
    {
        this.hourlyRate = hourlyRate;
    }

    public boolean isPartTime()
    {
        return partTime;
    }

    public void setPartTime(boolean partTime)
    {
        this.partTime = partTime;
    }

}

This class is self-explanatory. We declare a value bean named Employee and its attributes like id,name. And, we provide corresponding getter and setter methods.

Table Model Implementation:

Let us now extend the AbstractTableModel and override the methods that we need to:

package net.codejava.swing;

import java.util.List;
import javax.swing.table.AbstractTableModel;

import net.codejava.model.Employee;

public class EmployeeTableModel extends AbstractTableModel
{
    private final List<Employee> employeeList;
    
    private final String[] columnNames = new String[] {
            "Id", "Name", "Hourly Rate", "Part Time"
    };
    private final Class[] columnClass = new Class[] {
        Integer.class, String.class, Double.class, Boolean.class
    };

    public EmployeeTableModel(List<Employee> employeeList)
    {
        this.employeeList = employeeList;
    }
    
    @Override
    public String getColumnName(int column)
    {
        return columnNames[column];
    }

    @Override
    public Class<?> getColumnClass(int columnIndex)
    {
        return columnClass[columnIndex];
    }

    @Override
    public int getColumnCount()
    {
        return columnNames.length;
    }

    @Override
    public int getRowCount()
    {
        return employeeList.size();
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex)
    {
        Employee row = employeeList.get(rowIndex);
        if(0 == columnIndex) {
            return row.getId();
        }
        else if(1 == columnIndex) {
            return row.getName();
        }
        else if(2 == columnIndex) {
            return row.getHourlyRate();
        }
        else if(3 == columnIndex) {
            return row.isPartTime();
        }
        return null;
    }
}

This code shows a simple extension of the AbstractTableModel class. The model should hold data, so, we declare an instance variable which holds a list of employees. And we provide a constructor which takes a list as an argument. The no-args constructor is not provided here. This is because, we want to enforce the fact that the model is useless without any data.

We also declare a String array columnNames to hold the names of the headers. This is then used by the getColumnName() method to return the corresponding column header. Another array columnClass tells us which column is of which type. This variable is then used in the getColumnClass() method to return the corresponding type. The getColumnCount() method is supposed to return the number of columns to be displayed in the table. Instead of hardcoding the number as 4 (as we have 4 columns in our case), we have just used the columnName.length to return the value. This is very useful, as, later on, if we decide to increase the number of columns, we simply need to add more values to the array. The method as such can be left untouched.

The next method to be looked at it is the getRowCount(). This method should simply return the number of rows present in the table. And since we have a List variable, we can simply call the size() method on that and return the value. The number of rows is simply the number of employees in the organization which translates to number of employee instances in the list.

The final method to be looked at is getValueAt(). This method is slightly complex than the other methods. Like we discussed earlier, this method takes a row number and column number as parameters and should simply return the value that is to be displayed in that cell. In our case, the values come from the Employee value bean. So, we first get the Employee instance which corresponds to this row. We get this instance from the employee list by passing in the row number. Next, we check for the column number and make corresponding method call on the Employee instance to get the value and return it.

Using the Table Model:

Let us now attempt to use this model and build the table and display it:

package net.codejava.swing;

import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.SwingUtilities;
import net.codejava.model.Employee;

public class EditableTableExample extends JFrame
{
    public EditableTableExample()
    {
        Employee row1 = new Employee(1, "John", 40.0, false);
        Employee row2 = new Employee(2, "Rambo", 70.0, false);
        Employee row3 = new Employee(3, "Zorro", 60.0, true);
        
        //build the list
        List<Employee> employeeList = new ArrayList<Employee>();
        employeeList.add(row1);
        employeeList.add(row2);
        employeeList.add(row3);
        
        //create the model
        EmployeeTableModel model = new EmployeeTableModel(employeeList);
        //create the table
        JTable table = new JTable(model);
        
        //add the table to the frame
        this.add(new JScrollPane(table));
        
        this.setTitle("Editable Table Example");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        
        this.pack();
        this.setVisible(true);
    }
    
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new EditableTableExample();
            }
        });
    }    
}

We are now making use of the model that we wrote and building the display. We first create the data that is to be passed to the table for display. So, 3 instances of Employee class are created and and these are added to an ArrayList.

 @Override
    public void setValueAt(Object aValue, int rowIndex, int columnIndex)
    {
        Employee row = employeeList.get(rowIndex);
        if(0 == columnIndex) {
            row.setId((Integer) aValue);
        }
        else if(1 == columnIndex) {
            row.setName((String) aValue);
        }
        else if(2 == columnIndex) {
            row.setHourlyRate((Double) aValue);
        }
        else if(3 == columnIndex) {
            row.setPartTime((Boolean) aValue);
        }
    }

    @Override
    public boolean isCellEditable(int rowIndex, int columnIndex)
    {
        return true;
    }

package net.codejava.swing;

import java.util.List;
import javax.swing.table.AbstractTableModel;

import net.codejava.model.Employee;

public class EmployeeTableModel extends AbstractTableModel
{
    private final List<Employee> employeeList;
    
    private final String[] columnNames = new String[] {
            "Id", "Name", "Hourly Rate", "Part Time"
    };
    private final Class[] columnClass = new Class[] {
        Integer.class, String.class, Double.class, Boolean.class
    };

    public EmployeeTableModel(List<Employee> employeeList)
    {
        this.employeeList = employeeList;
    }
    
    @Override
    public String getColumnName(int column)
    {
        return columnNames[column];
    }

    @Override
    public Class<?> getColumnClass(int columnIndex)
    {
        return columnClass[columnIndex];
    }

    @Override
    public int getColumnCount()
    {
        return columnNames.length;
    }

    @Override
    public int getRowCount()
    {
        return employeeList.size();
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex)
    {
        Employee row = employeeList.get(rowIndex);
        if(0 == columnIndex) {
            return row.getId();
        }
        else if(1 == columnIndex) {
            return row.getName();
        }
        else if(2 == columnIndex) {
            return row.getHourlyRate();
        }
        else if(3 == columnIndex) {
            return row.isPartTime();
        }
        return null;
    }

    @Override
    public boolean isCellEditable(int rowIndex, int columnIndex)
    {
        return true;
    }

    @Override
    public void setValueAt(Object aValue, int rowIndex, int columnIndex)
    {
        Employee row = employeeList.get(rowIndex);
        if(0 == columnIndex) {
            row.setId((Integer) aValue);
        }
        else if(1 == columnIndex) {
            row.setName((String) aValue);
        }
        else if(2 == columnIndex) {
            row.setHourlyRate((Double) aValue);
        }
        else if(3 == columnIndex) {
            row.setPartTime((Boolean) aValue);
        }
    }

} 

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