A table cell renderer needs to implement a single method, TableCellRenderer.getTableCellRendererComponent() that returns a component. For performance reasons, the renderer should not create a new component each time getTableCellRendererComponent() is called. Rather, it should return the same component (or one from a set) every time. Typically, the renderer can either hold onto a component instance and return that component or it can be a subclass of a component and return itself. 
The job of getTableCellRendererComponent() is to configure the component based on the coordinates and value in the cell. The table then uses the configured component and paints it on the screen. After painting it, the table no longer needs the component. 

    JTable table = new JTable();
    // Add data...
    
    // Install the custom renderer on the first visible column
    int vColIndex = 0;
    TableColumn col = table.getColumnModel().getColumn(vColIndex);
    col.setCellRenderer(new MyTableCellRenderer());
    
    // This renderer extends a component. It is used each time a
    // cell must be displayed.
    public class MyTableCellRenderer extends JLabel implements TableCellRenderer {
        // This method is called each time a cell in a column
        // using this renderer needs to be rendered.
        public Component getTableCellRendererComponent(JTable table, Object value,
                boolean isSelected, boolean hasFocus, int rowIndex, int vColIndex) {
            // 'value' is value contained in the cell located at
            // (rowIndex, vColIndex)
    
            if (isSelected) {
                // cell (and perhaps other cells) are selected
            }
    
            if (hasFocus) {
                // this cell is the anchor and the table has the focus
            }
    
            // Configure the component with the specified value
            setText(value.toString());
    
            // Set tool tip if desired
            setToolTipText((String)value);
    
            // Since the renderer is a component, return itself
            return this;
        }
    
        // The following methods override the defaults for performance reasons
        public void validate() {}
        public void revalidate() {}
        protected void firePropertyChange(String propertyName, Object oldValue, Object newValue) {}
        public void firePropertyChange(String propertyName, boolean oldValue, boolean newValue) {}
    }