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Tip of the Day
Language: Java
Expertise: Intermediate
Jun 11, 1999

Duplicates in a Swing ComboBox

Swing's JComboBox can be used to present a drop-down list, perhaps of status reports from a process, requiring minimal screen space until the user wishes to see the details. But you run into a problem when there are duplicate entries in the list. The setSelectedIndex method causes the first occurrence of the element at the specified index to be highlighted, which is not necessarily at the given index. If the fifth and tenth elements are the same and your code says:

 
    combo.setSelectedIndex(10);

then the fifth element will be highlighted. You could call this a bug or a design flaw, but this tiny class provides a workaround:

 
    public class StringWithoutEqual
    {
        private String text;
    // Constructor
        public StringWithoutEqual(String txt)
        {
            text = txt;
        }
    // Method
        public String toString()
        {
            return text;
        }
    }

When you add a String to the combo box, use:

 
    yourBox.addItem(new StringWithoutEqual(yourString));

The toString method will be used to render the element, just as if you had provided the String directly. But because the class inherits the equals method from the Object class, the JComboBox will not be aware of any duplicates.

Tom Yarker
 
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