Name: rmT116609 Date: 08/22/2004


A DESCRIPTION OF THE REQUEST :
The current SpringLayout implements only allow developers to specify the "relative position" of one component of another by setting a constraint, while it doesn't know the "reverse meaning" of the constraint. This produces a rather surprising behavior.

Try the following code and you see the problem.

As you can see, there are four components, laying out from left to right:
(1) JLabel
(2) JTextField
(3) two JButtons

If we change the first constraint setting line
from
      layout.putConstraint(SpringLayout.WEST, inputLabel, 10,
        SpringLayout.WEST, this);

to
     layout.putConstraint(SpringLayout.WEST, this, 10,
       SpringLayout.WEST, inputLabel);

 And this behavior is rather counter intuitive because the two statements are "conceptually" the same thing. When there are a lot of components on the screen, it would be very difficult to resolve such situation because the relations are simply too complex to be resolved.

I wonder if the SpringLayout implement could produce the "implicit constraint" internally, the code would be much cleaner and easier to write.


JUSTIFICATION :
Reduce the amount of error-prone constraint setting code. It is very hard to make things laid out correctly if there are a lot of components within a single container.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
chaning the first constraint line
from
      layout.putConstraint(SpringLayout.WEST, inputLabel, 10,
        SpringLayout.WEST, this);

to
     layout.putConstraint(SpringLayout.WEST, this, 10,
       SpringLayout.WEST, inputLabel);

means the same thing...
ACTUAL -
chaning the first constraint setting line
from
      layout.putConstraint(SpringLayout.WEST, inputLabel, 10,
        SpringLayout.WEST, this);

to
     layout.putConstraint(SpringLayout.WEST, this, 10,
       SpringLayout.WEST, inputLabel);

---------- BEGIN SOURCE ----------
      SpringLayout layout=(SpringLayout) super.getLayout();
      inputLabel=new JLabel();
      inputField=new JTextField();
      submitButton=new JButton();
      clearButton=new JButton();
      // call this to set the localized labels
      refreshLabels();
      // add the components.
      add(inputLabel);
      add(inputField);
      add(submitButton);
      add(clearButton);
      
      // set the spring constraints.
      layout.putConstraint(SpringLayout.WEST, inputLabel, 10,
        SpringLayout.WEST, this);
      layout.putConstraint(SpringLayout.WEST, inputField, 5,
        SpringLayout.EAST, inputLabel);
        
      layout.putConstraint(SpringLayout.WEST, submitButton, 10,
        SpringLayout.EAST, inputField);
      layout.putConstraint(SpringLayout.WEST, clearButton, 5,
        SpringLayout.EAST, submitButton );
      layout.putConstraint(SpringLayout.EAST, this, 10,
        SpringLayout.EAST, clearButton);

---------- END SOURCE ----------


(Incident Review ID: 232691)
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