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Graphical User Interface Objects and Events

Lists, combo boxes and other selection controls

  • 3 things to know
  • AS Unit 2

Overview

List box, editable combo box and multiple selection list.

What you need to know

Answer each one before you reveal it.

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Key term

A list box is empty and the code asks for the selected index. State the value returned and why the program must check it.

Key term

What is a list box?

Key term

How does a combo box differ from a list box?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a list box?

    Model answer

    A list box shows several entries at once and lets the user select one or more of them by clicking.

  2. 2

    How does a combo box differ from a list box?

    Model answer

    A combo box shows only the current selection until the user opens the drop-down, so a combo box takes one line of the form instead of several.

  3. 3

    What is an editable combo box?

    Model answer

    An editable combo box lets the user type a value that is not in the list as well as choose one from the drop-down.

  4. 4

    The Java code cboSize.addItem("Small"); cboSize.addItem("Medium"); cboSize.addItem("Large"); runs on an empty combo box and nothing else is selected. What does cboSize.getSelectedIndex() return?

    Model answer

    The call returns 0, because the first entry added to an empty combo box becomes the selection and entry positions are counted from zero.

  5. 5

    A combo box has had Small, Medium and Large added in that order and the user has chosen the third entry. What do getSelectedIndex and getSelectedItem each return?

    Model answer

    The index call returns 2 because counting starts at zero and Large is two places along, and the item call returns the wording Large.

  6. 6

    Why is a selection control safer than a text box for a field such as county?

    Model answer

    A selection control offers only valid entries, so misspellings and unexpected wording never reach the program or the file.

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