Channels ▼


Java: Better Interfaces via JFormattedTextField


The MaskFormatter is best used to format Strings that have a fixed length and set format. Examples include: dates, Social Security Numbers, phone numbers, credit-card numbers, ZIP codes, vehicle ID numbers (VINs). MaskFormatters are not suitable for Strings with variable numbers of characters, e.g. URLs and email addresses. A single instance of the MaskFormatter can be used for both the edit and display formats of an AbstractFormatterFactory. A MaskFormatter object is created using a constructor that accepts a formatting mask as its only parameter. The formatting mask specifies what type of characters can appear in each position and any literal characters. Literal characters are fixed in place and are not changeable by the users; for example, the dash and parenthesis in a phone number would be considered literal characters. Table 2 shows the different mask characters used by the MaskFormatter.

Table 2: MaskFormatter Characters.

For example, the mask "###-##-####" could be used for a Social Security number. The #s allow the user to type in any number, the dashes are literals and fixed in place. Similarly for a ZIP code the mask "#####-####" could be used:

MaskFormatter zipMask = new MaskFormatter("#####-####");
MaskFormatter ssnMask = new MaskFormatter("###-##-####");

You can restrict what the user types in even more by invoking the setValidCharacters or the setInvalidCharacters method. For example, if you wanted to restrict the digits in a ZIP code to just 2s and 3s, then you could make the following call:

zipMask.setValidCharacters("23");  // only allow 2, 3 in the zip code

Alternatively, if you wanted any digit but a 2 or a 3 then you could make the following call:

zipMask.setInvalidCharacters("23"); // don't allow 2,3 in the zip code.

A final consideration when creating a MaskFormatter is setting the placeholder character. This character is inserted into the String if the current value has too few characters or when the user presses the delete or backspace keys while editing. It is common to use an underscore as the placeholder, but any character will do. To avoid confusion, select a character that is not used as a literal or valid character in the mask. To set the placeholder, call the setPlaceholderCharacter method; for example:

zipMask.setPlaceholderCharacter('_');  // use an underscore as a placeholder

The Table 3 provides a few common masks.

Table 3: Masks for common data types.

(You may want to consider using a fixed-width font (such as Courier) for the JFormattedTextField. This makes the overall appearance and character spacing more pleasing to the eye.

The example below creates a JFormattedTextField for entering a Date:

 // create a MaskFormatter for Dates
 JFormattedTextField dateField = new JFormattedTextField();
 MaskFormatter dateFormatter = new MaskFormatter("##/##/#### ##:##:## UM");
 DefaultFormatterFactory dateFormatterFactory = new 

The example below creates a JFormattedTextField for entering a Social Security number:

JFormattedTextField ssnField = new JFormattedTextField();
MaskFormatter ssnFormatter = new MaskFormatter("###-##-####");
DefaultFormatterFactory ssnFormatterFactory = new 

Related Reading

More Insights

Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.