Question

I’m using a 2010 Mac with 1.6.0_37 Java, using DrJava to compile. The revalidate method does not compile, and I receive the following error:

2 errors found:
File: /Users/#########/compsci/Final/ConnectFourFrame.java  [line: 123]
Error: /Users/#########/compsci/Final/ConnectFourFrame.java:123: cannot find symbol
symbol  : method revalidate()
location: class ConnectFourFrame

This is the method giving rise to the error:

try 
{ 
  //display in window 
  updateTitleBar(); 
  ObjectInputStream ois = new ObjectInputStream(new FileInputStream(currentFile)); 
  colorGrid = (Color[][]) ois.readObject(); 
  makeGrid(); 
  for(int k = 0; k < 6; k++) 
  { 
    for(int l = 0; l < 7; l++) 
    { 
      if (colorGrid[k][l]==null) 
      { 
        grid[k][l] = new BlankTile(new Point(k, l)); 
      } 
      else if (colorGrid[k][l].equals(Color.red)) 
      { 
        grid[k][l] = new RedTile(new Point(k, l)); 
      } 
      else if (colorGrid[k][l].equals(Color.black)) 
      { 
        grid[k][l] = new BlackTile(new Point(k, l)); 
      }                              
    } 
  }                        
  putNewGrid(); 
  String currentColor = (String) ois.readObject(); 
  ois.close(); 
  ConnectFourFrame.this.repaint(); 
  ConnectFourFrame.this.revalidate();  //This is the offending line
  gp.revalidate(); 
  gp.repaint(); 
}

And the outer class is ConnectFourFrame (extends JFrame and implements Runnable)

How can I resolve this issue?

Answer 1

Component.revalidate() is new in Java 7. Presumably you’re using 7 on Windows as opposed to 6 on Mac.

If you need your code to work on Java 6 then you’ll have to do things differently. The JavaDoc for Component.revalidate says

This is a convenience method supposed to help application developers avoid looking for validate roots manually. Basically, it’s equivalent to first calling the invalidate() method on this component, and then calling the validate() method on the nearest validate root.

Since a JFrame is itself a validate root, you should just be able to replace the revalidate call with invalidate() followed by validate().