Use JRadioButtonMenuItem and JCheckBoxMenuItem - Swing

Use JRadioButtonMenuItem and JCheckBoxMenuItem

Although the type of menu items used by the preceding examples are, as a general rule, the most commonly used, Swing defines two others: check boxes and radio buttons. These items can streamline a GUI by allowing a menu to provide functionality that would otherwise require additional, stand-alone components. Also, sometimes, including check boxes or radio buttons in a menu simply seems the most natural place for a specific set of features. Whatever your reason, Swing makes it easy to use check boxes and radio buttons in menus, and both are examined here.

To add a check box to a menu, create a JCheckBoxMenuItem. It defines several constructors. This is the one used in this chapter:

JCheckBoxMenuItem(String name)

Here, name specifies the name of the item. The initial state of the check box is unchecked. If you want to specify the initial state, you can use this constructor:

JCheckBoxMenuItem(String name, boolean state)

In this case, if state is true, the box is initially checked. Otherwise, it is cleared. JCheckBoxMenuItem also provides constructors that let you specify an icon. Here is one example:

JCheckBoxMenuItem(String name, Icon icon)

In this case, name specifies the name of the item and the image associated with the item is passed in icon. The item is initially unchecked. Other constructors are also supported.

Check boxes in menus work like stand-alone check boxes. For example, they generate action events and item events when their state changes. Check boxes are especially useful in menus when you have options that can be selected and you want to display their selected/ deselected status.

A radio button can be added to a menu by creating an object of type

JRadioButtonMenuItem. JRadioButtonMenuItem inherits JMenuItem. It provides a rich assortment of constructors. The ones used in this chapter are shown here:

JRadioButtonMenuItem(String name) JRadioButtonMenuItem(String name, boolean state)

The first constructor creates an unselected radio button menu item that is associated with the name passed in name. The second lets you specify the initial state of the button. If state is true, the button is initially selected. Otherwise, it is deselected. Other constructors let you specify an icon. Here is one example:

JRadioButtonMenuItem(String name, Icon icon, boolean state)

This creates a radio button menu item that is associated with the name passed in name and the image passed in icon. If state is true, the button is initially selected. Otherwise, it is deselected. Several other constructors are supported.

A JRadioButtonMenuItem works like a stand-alone radio button, generating item and action events. Like stand-alone radio buttons, menu-based radio buttons must be put into a button group in order for them to exhibit mutually exclusive selection behavior.

Because both JCheckBoxMenuItem and JRadioButtonMenuItem inherit JMenuItem, each has all of the functionality provided by JMenuItem. Aside from having the extra capabilities of check boxes and radio buttons, they act like and are used like other menu items.

To try check box and radio button menu items, first remove the code that creates the Options menu in the MenuDemo example program. Then substitute the following code sequence, which uses check boxes for the Colors submenu and radio buttons for the Priority submenu. After making the substitution, the Options menu will look like those shown in Figure 33-4.

//   Create    the Options   menu.

JMenu     jmOptions = new    JMenu("Options");

//   Create    the Colors    submenu.

JMenu     jmColors = new JMenu("Colors");

     //Use check boxes for colors. This allows

     //the user to select more than one color.

     JCheckBoxMenuItem jmiRed = new JCheckBoxMenuItem("Red"); JCheckBoxMenuItem jmiGreen = new JCheckBoxMenuItem("Green"); JCheckBoxMenuItem jmiBlue = new JCheckBoxMenuItem("Blue");

jmColors.add(jmiRed);

jmColors.add(jmiGreen);

jmColors.add(jmiBlue);

jmOptions.add(jmColors);

// Create the Priority submenu.

JMenu jmPriority = new JMenu("Priority");

     //Use radio buttons for the priority setting.

     //This lets the menu show which priority is used

     //but also ensures that one and only one priority

     //can be selected at any one time. Notice that

     //the High radio button is initially selected.

     JRadioButtonMenuItem jmiHigh =

new JRadioButtonMenuItem("High", true);

JRadioButtonMenuItem jmiLow =

new JRadioButtonMenuItem("Low");

jmPriority.add(jmiHigh);

jmPriority.add(jmiLow);

jmOptions.add(jmPriority);

     //Create button group for the radio button menu items.

     ButtonGroup bg = new ButtonGroup();

bg.add(jmiHigh);

bg.add(jmiLow);

     //Create the Reset menu item.

JMenuItem jmiReset = new JMenuItem("Reset");

jmOptions.addSeparator(); jmOptions.add(jmiReset);

     //Finally, add the entire options menu to

     //the menu bar

jmb.add(jmOptions);