JRadioButton

A radio button group exists to allow the user to select a single option from a group of options. When radio buttons are part of a radio button group then only one of them can be selected at any one time. You can use the JRadioButton class to implement radio buttons. You can also put radio buttons in menus using the JRadioButtonMenuItem class.

There are no less than seven constructors that can be used to create a JRadioButton because you have the choice of creating a radio button with a normal circular selection area or a radio button where the circular selection area is replaced by an image.

`JRadioButton()`	Creates a radio button with no text, no icon, unselected
`JRadioButton(String s)`	Creates a radio button with the specified text, no icon, unselected
`JRadioButton(String s, boolean b)`	Creates a radio button with the specified text, no icon, and selected if b is true
`JRadioButton(Icon m)`	Creates a radio button with no text, the specified image, unselected
`JRadioButton(Icon m, boolean b)`	Creates a radio button with no text, the specified image, and selected if b is true
`JRadioButton(String s, Icon m)`	Creates a radio button with the specified text, the specified image, unselected
`JRadioButton(String s, Icon m, boolean b)`	Creates a radio button with the specified text, the specified image, and selected if b is true

Plain JRadioButton

To create a plain unselected radio button, we can use the second constructor listed in the table above, with a line of code such as:-

JRadioButton eyeballRadio = new JRadioButton("Sir EyeBall");

Using the third constructor listed in the table above, I could create a plain radio button with the circular selection area initially in a selected state:-

JRadioButton eyeballRadio = new JRadioButton("Sir EyeBall", true);

The applet below shows a group of radio buttons with plain circular selection areas, all of them initially unselected. These radio buttons were added to a ButtonGroup so only one can be selected at a time.

~~~Applet~~~

Image JRadioButton

You can specify images to be used in place of the standard selected and unselected circular area. To do this we need to create an Icon. We can use the ImageIcon class for this:-

ImageIcon imgUnselected = new ImageIcon (getImage

(getCodeBase(),"sadface.gif"));

Then we can use the variable that references the ImageIcon object in the argument for the radio button's constructor:-

JRadioButton frogRadio = new JRadioButton("Frog Dance", imgUnselected);

The image specified at radio button creation time is the image that will be used for the unselected state. This means we have to specify another image to be used when the radio button is in the selected state. To do this use code such as:-

ImageIcon imgSelected = new ImageIcon (getImage

(getCodeBase(),"happyface.gif"));

frogRadio.setSelectedIcon(imgSelected);

Don't forget to place your image file in the same folder as you class file.

The applet below shows image radio buttons. I have specified an image of a smiley face and an image of a unsmiley face to be used in place of the standard selected and unselected circular area.

~~~Applet~~~

Important: -- Using images in applets?

Then read this to understand how to include images in web page applets using lines of code like:-

ImageIcon imgUnselected = new ImageIcon (getImage

(getCodeBase(),"sadface.gif"));

Don't forget to import the package java.net.*

Other JRadioButton Methods

Here are some methods we can use with the JRadioButton class. You should note that this is not a full list, there are lots of other methods. These are a similar set of methods to those of the JButton and JCheckbox class, since they all inherit from JComponent and AbstractButton.

You should check out the inherited JComponent and JAbstractButton class methods.

`setText(String s)`	Set the text displayed by the radio button.
`setEnabled(boolean b);`	Enable or disable the radio button using `true` or `false` as the argument
`setFont(Font f)`	Set the font of the text on the radio button
`setHorizontalTextPosition(int i)`	Set the horizontal position of the radio button's text relative to the button's image using as the argument: `JRadioButton.LEFT, JRadioButton.CENTER or JRadioButton.RIGHT`.
`setVerticalTextPosition(int i)`	Set the vertical position of the radio button's text relative to the buttons image using as the argument: `JRadioButton.TOP, JRadioButton.CENTER or JRadioButton.BOTTOM`.
`setToolTiptext(String s)`	Add a tool tip that appears when the cursor is over the radio button.
`setSelected(boolean b)`	Sets the radio button to selected if b is true else set it to unselected.
`boolean isSelected()`	Returns true if the radio button is selected and false if is unselected.
`setSelectedIcon(Icon m)`	Sets the image to be used when the radio button is in the selected state.
`setRolloverIcon(Icon m)` `setRolloverEnabled(boolean b)`	Use `setRolloverIcon(Icon m)` with `setRolloverEnabled(true)`to make the radio button display the specified icon when the cursor passes over it.

~Now try the activity~

Activity A

Using appropriate methods from the JCheckBox, JAbstractButton and JComponent class, create an applet with ...

at least one panel to contain some radio buttons

four radio buttons similar to the first applet shown on this page

set the font color of the radio button labels to any color of your choice, (apart from black).

set the font of the radio button labels to Arial, italic and 10 points in size. The Font class is explained in the Graphics tutorial.

set the panel background color to any color of your choice

JRadioButton Groups

It is normal to group radio buttons together so that only one can be selected at any one time. If you have completed the activity above you may notice that it is possible to select more than one of the radio buttons at any one time.

For instance, here is the code for creating four JRadioButtons:-

JRadioButton penguinSetButton = new JRadioButton ("Penguin Set"); JRadioButton coolPenguinButton = new JRadioButton ("Cool Penguin"); JRadioButton snakeButton = new JRadioButton ("Madam Snake"); JRadioButton eyeballButton = new JRadioButton ("Sir Eyeball");

The picture shows these radio buttons and as we can see, more than one of them can be selected at a time.

It is not difficult to change this so that only one is ever selected out of a group.

We just have to create a ButtonGroup instance and add the radio buttons to this group:-

// create a ButtonGroup

myButtonGroup = new ButtonGroup();

// add the radio buttons to the ButtonGroup myButtonGroup.add(penguinSetButton); myButtonGroup.add(snakeButton); myButtonGroup.add(coolPenguinButton); myButtonGroup.add(eyeballButton);

That's it. Now these radio buttons act as a mutually exclusive selection group.

~Now try the activity~

Activity B