Passing data between forms

Overview

Shared data class, one disadvantage of holding data in public global variables and callback used for between forms.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Name three ways of getting a value from one form to another.

   Model answer

   A value is passed through the second form's constructor, set through a public method on it, or held in a shared class both forms can reach.

2. 2

   What is the advantage of passing a value through the constructor of the second form?

   Model answer

   A constructor parameter makes the value compulsory, so the second form can never be created without the data it needs to work.

3. 3

   The Java code FrmEdit f = new FrmEdit("Ana Kelly"); f.setVisible(true); runs, and FrmEdit's constructor contains txtName.setText(n); where n is the parameter. What does the user see?

   Model answer

   The user sees the edit window open with Ana Kelly already in the name box, because the constructor copied the parameter into the text box before the window appeared.

4. 4

   How does a modal dialog return a value to the form that opened it?

   Model answer

   The dialog stores the value in one of its own fields, and the calling form reads that field through a getter once the show call returns.

5. 5

   Why can the calling form not read a modeless form's fields immediately after showing it?

   Model answer

   The show call returns at once for a modeless form, so the user has not yet entered anything and the fields still hold their starting values.

6. 6

   What is a shared data class, and why is one used across forms?

   Model answer

   A shared data class is a single object holding the application's working data, and every form reads and writes it so all the screens agree.

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