Suppose I am creating a custom JTable with CustomDataModel and CustomTableListener. Suppose they work gloriously.
Now suppose in the implementation that every JTable is guaranteed to have its first row populated with type-safe data, and that that data will never get deleted, only modified - and never set to null. (using JComboBoxes as their editor, and empty String's and 0's that get rendered as empty strings are the only "empty" choice)
Now; I want to write a method that uses getColumnClass to return typed-data.
From what I've read I'll have to use the following methods in conjunction:
class CustomDataModel extends AbstractTableModel {
...
//implement data struc and other methods (full testable code further down below in the SSCCE)
...
/**
* Guaranteed to return a class based on this table's construction
* @param c
* @return
*/
@Override
public Class getColumnClass(int c){
return getValueAt(0,c).getClass();
}
...
public <T> T returnType(int row, int column) {
//the following will not compile - and I'm stuck, don't know how to
//use getColumnClass to return type-specific data
return getColumnClass(column).cast(getValueAt(row,column));
}
}
NetBeans tells me that the cast invocation returns Object, but I was sure that cast(Object obj) returned T, where T is the type of this in cast.
The more I think about it, the more that I believe that I what I desire is impossible. It's not really necessary, but it would avoid casts - although I suppose this would force casts to be done if my current implementation gets "fixed" and typed-retrieval done through manual casting.
Now; in the SSCCE I use system.out.println to just print - which takes in an Object reference and invokes its toString() method, but the methods or actions I want to take I don't necessarily want to be bound to an Object parameter.
The point is to directly get the type of the data stored; which isn't really possible if it's stored as an Object reference without casting it back to its original type I suppose... Unless generics are used? I don't know - any help appreciated!
SSCCE
//package utility;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.AbstractTableModel;
/**
* @author Sean
*/
public class UnitTesting extends JPanel{
public UnitTesting() {
super(new GridLayout(1,0));
JTable table = createAJTable();
table.getTableHeader().setReorderingAllowed(false);
table.setPreferredScrollableViewportSize(new Dimension(500, 70));
table.setFillsViewportHeight(true);
//Create the scroll pane and add the table to it.
JScrollPane scrollPane = new JScrollPane(table);
//Normally here JComboBoxes are set as the Editors - SSCCE will use dummy test data
//Add the scroll pane to this panel.
add(scrollPane);
//Test the data Types - I want to retrieve type-specific data to avoid casting
CustomModel dataModel = (CustomModel)table.getModel();
Object val;
for(int row = 0; row < dataModel.getRowCount(); row++){
//Row possibility
doSomeThings(row, dataModel);
for(int col = 0; col < dataModel.getColumnCount(); col++){
//Here's the old way of going about this. (also could invoke getColumnClass())
val = dataModel.getValueAt(row, col);
System.out.println(val + " : " + val.getClass());
//Overloaded possibility - needs typed data
// doSomeAction(dataModel.typedValueAt(row, col));
}
}
}
private JTable createAJTable() {
return new JTable(new CustomModel(new String[]{"Col1", "Col2", "Col3", "Col4", "Col5"}));
}
private void doSomeAction(String str){
//Do things with strings
}
private void doSomeAction(int number){
//Do things with integers
}
private void doSomeThings(int row, CustomModel dataModel) {
String col1Data, col2Data, col5Data;
int col3Num, col4Num;
//Retrieve data and store it in typed local variable (need casting or typed retrieval)
//Do things with the Strings and Integers together
}
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("TableDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
UnitTesting newContentPane = new UnitTesting();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
/*
* Set Look and feel here; taken out for SSCCE
*/
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
createAndShowGUI();
}
});
}
class CustomModel extends AbstractTableModel {
//Dummy data for the SSCCE
private List<String> columnHeadings;
private List<List<Object>> data;
CustomModel(String[] cols){
data = new ArrayList<>();
columnHeadings = Arrays.asList(cols);
ArrayList<Object> testRow = new ArrayList<>();
testRow.add("String");
testRow.add("Str");
testRow.add(0);
testRow.add(5);
testRow.add("Strong");
data.add(testRow);
}
//This is the method I want to create
// public <T> T typedValueAt(int row, int column) {
// return getColumnClass(column).cast(getValueAt(row,column));
// }
@Override
public int getRowCount() {
return data.size();
}
@Override
public int getColumnCount() {
return columnHeadings.size();
}
@Override
public String getColumnName(int columnIndex) {
return columnHeadings.get(columnIndex);
}
@Override
public Class<?> getColumnClass(int c) {
return getValueAt(0,c).getClass();
}
@Override
public boolean isCellEditable(int rowIndex, int columnIndex) {
//For the SSCCE we'll just test with one row of uneditable data
return false;
}
@Override
public Object getValueAt(int rowIndex, int columnIndex) {
return data.get(rowIndex).get(columnIndex);
}
@Override
public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
//Normally check for row existence and populate necessary rows - but for SSCCE just this will suffice
data.get(rowIndex).set(columnIndex, aValue);
}
}
}
