从另一个类引用 JTable

Question

Java newbie here. I am using NetBeans 11.2. I am making a GUI awt app, I have a main class as a JFrame, and I need to reference the JTable on it or its model from another class.

Not to overload this post with lots of code, I created a tiny project from the tutorial on the Oracle site . Basically, a project named "CelciusConverterProject", a JFrame named "CelciusconverterGUI" as main class in package "learn". Then I plopped a jTable1 onto the frame and added a getter to CelciusconverterGUI for the table model named "getMdl()" :

package learn;

import javax.swing.table.DefaultTableModel;

public class CelsiusConverterGUI extends javax.swing.JFrame {

[...]

          /* Create and display the form */
          java.awt.EventQueue.invokeLater(new Runnable() {
               public void run() {
                    new CelsiusConverterGUI().setVisible(true);
               }
          });
     }

     // Variables declaration - do not modify                     
     private javax.swing.JScrollPane jScrollPane1;
     private javax.swing.JTable jTable1;
     // End of variables declaration                   

     public DefaultTableModel getMdl() {
          return (DefaultTableModel) this.jTable1.getModel();
     }

}

No errors so far, the Navigator pane shows getMdl as a public method.

Now I have created a new class called "Testing", but I cannot figure out how to call getMdl() from the instantiated running JFrame:

package learn;

import javax.swing.table.DefaultTableModel;

public class Testing {

     tmdl = (DefaultTableModel) <...>

}

Neither

 tmdl = new (DefaultTableModel) learn.CelsiusConverterGUI.

nor

 tmdl = (DefaultTableModel) learn.CelsiusConverterGUI.

is showing me my getter in the code completion window.

Probably a totally noobish question, but sorry I can't even google anyone who has asked the same question.

Answer 1

You say you are "...making a Java awt app...", but you are using Swing classes. AWT is a Java UI library, and Swing is a different Java UI library that still uses some AWT components. But I think it's more useful and more accurate to say that you're writing a Java Swing app.

Your getMdl() method returns a DefaultTableModel -- does it need to return something that specific? Especially when you're just starting, it will be simpler if you can work with existing libraries without casting any more than you need to. The JTable.getModel() method returns TableModel , an interface ( https://docs.oracle.com/javase/7/docs/api/javax/swing/table/TableModel.html ) that guarantees that whatever object is returned will implement all the methods in the interface. So unless you need to call a method that is in DefaultTableModel and is not in TableModel , then you can eliminate the castings to DefaultTableModel (the (DefaultTableModel) you have in a couple of places.

It is possible the code completion is confused by this casting -- if you were, in fact, attempting to cast CelsiusConverterGUI to DefaultTableModel , then it would not show you the getMdl() method because that doesn't exist in DefaultTableModel . I know you were probably trying to cast the return of getMdl() to DefaultTableModel , but the code completion logic may not realize that.

So my recommendation is to have getMdl() return TableModel and eliminate all casting to DefaultTableModel . I think your code completion will then show you getMdl() in your `CelsiusConverterGUI' class.

One more thing: Java convention calls for spelling out words in names of things; most Java programmers would use and expect getModel() instead of getMdl() .

Answer 2

I'm adding another answer because we now have a better definition of the question.

You want to get a reference to the CelsuisConverterGUI object that you instantiated; to do that, you need to assign the result of the instantiation of the class to a variable and then obtain that reference somehow. Below is an example that I have not even compiled, but should be close -- it has a static variable that keeps the (only) reference to the main class, and instantiates the class the first time the getter for the instance is used:

public class CelsiusConverterGUI extends JFrame
{
  private static CelsiusConverterGUI mainFrame = null;
  public static getMainFrame() 
  { 
    if (mainFrame == null)
    {
      java.awt.EventQueue.invokeAndWait(new Runnable() { mainFrame = new CelsiusConverter(); }
    }
    return mainFrame; 
  }

  public static void main(String ... arguments)
  {
    java.awt.EventQueue.invokeLater(new Runnable()
    {
      mainFrame = getMainFrame();
      mainFrame.setVisible(true);
    }
  }

  // ...
}

public class Testing
{
  CelsiusConverterGUI mainFrame = CelsiusConverterGUI.getMainFrame();
  // ...
}