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How to Use Sliders

Use a JSlider to let the user enter a numeric value bounded by a minimum and maximum value. By using a slider instead of a text field, you eliminate input errors.

Here's a picture of an application that uses a slider to control animation speed:

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Try this: 

1. Compile and run the application. The source file is SliderDemo.java. You will also need the image files that compose the animation. See the examples index for links to all the files required by this example.
   See Getting Started with Swing if you need help compiling or running this application.
2. Use the slider to adjust the animation speed.
3. Push the slider to 0 to stop the animation.

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Below is the code from SliderDemo.java that creates the slider in the previous example.

JSlider framesPerSecond = new JSlider(JSlider.HORIZONTAL,
                                      0, 30, FPS_INIT);
framesPerSecond.addChangeListener(new SliderListener());
framesPerSecond.setMajorTickSpacing(10);
framesPerSecond.setMinorTickSpacing(1);
framesPerSecond.setPaintTicks(true);
framesPerSecond.setPaintLabels(true);
framesPerSecond.setBorder(BorderFactory.createEmptyBorder(0,0,10,0));
. . .
//add the slider to the content pane
contentPane.add(framesPerSecond);

By default, spacing for major and minor tick marks is zero. To see tick marks, you must explicitly set the spacing for either major or minor tick marks (or both) to a non-zero value and call setPaintTicks(true). Just calling setPaintTicks(true) is not enough. To display standard, numeric labels at major tick mark locations, set the major tick spacing, then call setPaintLabels(true). The example program provides labels for its slider this way. But you don't have to settle for these labels. Customizing Labels on a Slider shows you how to customize slider labels.

When you move the slider's knob, the stateChanged method of the slider's ChangeListener is called. For information about change listeners, refer to How to Write a Change Listener. Here is the code for this example's change listener:

class SliderListener implements ChangeListener {
    public void stateChanged(ChangeEvent e) {
        JSlider source = (JSlider)e.getSource();
        if (!source.getValueIsAdjusting()) {
	    int fps = (int)source.getValue();
	    if (fps == 0) {
	        if (!frozen) stopAnimation();
	    } else {
	        delay = 1000 / fps;
	        timer.setDelay(delay);
	        timer.setInitialDelay(delay * 10);
	        if (frozen) startAnimation();
	    }
        }
    }
}

Notice that our stateChanged method changes the animation speed only if getValueIsAdjusting returns false. Many change events are fired as the user moves the slider knob. This program is interested only in the final result of the user's action.

Customizing Labels on a Slider

Shown below is a modified version of the previous program that uses a slider with custom labels:

You can find the source for this program in SliderDemo2.java. As with the other example, you also need the image files that compose the animation. See the examples index for links to all the files required by this example.

The following code creates the slider and customizes its labels:

//Create the slider
JSlider framesPerSecond = new JSlider(JSlider.VERTICAL,
                                      0, 30, FPS_INIT);
framesPerSecond.addChangeListener(new SliderListener());
framesPerSecond.setMajorTickSpacing(10);
framesPerSecond.setPaintTicks(true);

//Create the label table
Hashtable labelTable = new Hashtable();
labelTable.put( new Integer( 0 ), new JLabel("Stop") );
labelTable.put( new Integer( 3 ), new JLabel("Slow") );
labelTable.put( new Integer( 30 ), new JLabel("Fast") );
framesPerSecond.setLabelTable( labelTable );

framesPerSecond.setPaintLabels(true);
framesPerSecond.setBorder(BorderFactory.createEmptyBorder(0,0,0,10));

Each key-value pair in a Hashtable specifies the position and the value of one label. The hashtable key must be an Integer and is a value within the slider's range at which to place the label. The hashtable value must be a Component. This program uses JLabel instances with text only. An interesting variation would be to use JLabel instances with icons, or perhaps buttons that move the knob to the label's position.

If you want a set of numeric labels positioned at a specific interval, you can use JSlider's createStandardLabels method to create the Hashtable for you. You can also modify the table returned by createStandardLabels to then customize it.

The Slider API

The following tables list the commonly used JSlider constructors and methods. See The JComponent Class for tables of commonly used inherited methods.

The API for using sliders falls into these categories:

• Creating the Slider
• Fine Tuning the Slider's Appearance
• Watching the Slider Operate

Creating the Slider

Constructor	Purpose
JSlider()	Creates a horizontal slider with the range 0 to 100 and an initial value of 50.
JSlider(int min, int max) JSlider(int min, int max, int value)	Creates a horizontal slider with the specified minimum and maximum values. The third int argument, when present, specifies the slider's initial value.
JSlider(int orientation) JSlider(int orientation, int min, int max, int value)	Creates a slider with the specified orientation, which must be either JSlider.HORIZONTAL or JSlider.VERTICAL. The last three int arguments, when present, specify the slider's minimum, maximum, and initial values, respectively.
JSlider( BoundedRangeModel)	Creates a horizontal slider with the specified model, which manages the slider's minimum, maximum, and current values and their relationship.

Fine Tuning the Slider's Appearance

Method	Purpose
void setValue(int) int getValue()	Set or get the slider's current value. This method also positions the slider's knob.
void setOrientation(int) int getOrientation()	Set or get the orientation of the slider. Possible values are JSlider.HORIZONTAL or JSlider.VERTICAL.
void setInverted(boolean) boolean getInverted()	Set or get whether the maximum is shown at the left of a horizontal slider or at the bottom of a vertical one, thereby inverting the slider's range.
void setMinimum(int) int getMinimum() void setMaximum(int) int getMaximum()	Set or get the minimum or maximum values of the slider. Together, these methods set or get the slider's range.
void setMajorTickSpacing(int) int getMajorTickSpacing() void setMinorTickSpacing(int) int getMinorTickSpacing()	Set or get the range between major and minor ticks. You must call setPaintTicks(true) for the tick marks to appear.
void setPaintTicks(boolean) boolean getPaintTicks()	Set or get whether tick marks are painted on the slider.
void setPaintLabels(boolean) boolean getPaintLabels()	Set or get whether labels are painted on the slider. You can provide custom labels with setLabelTable or get automatic labels by setting the major tick spacing to a non-zero value.
void setLabelTable(Dictionary) Dictionary getLabelTable()	Set or get the labels for the slider. You must call setPaintLabels(true) for the labels to appear. createStandardLabels is a convenience method for creating a standard set of labels.
Hashtable createStandardLabels(int) Hashtable createStandardLabels(int, int)	Create a standard set of numeric labels. The first int argument specifies the increment, the second int argument specifies the starting point. When left unspecified, the slider's minimum is used as the starting point.

Watching the Slider Operate

Method	Purpose
void addChangeListener(ChangeListener)	Register a change listener with the slider.
boolean getValueIsAdjusting()	Determine whether the user gesture to move the slider's knob is complete.

Examples that Use Sliders

This table shows the examples that use JSlider and where those examples are described.

Example	Where Described	Notes
SliderDemo	This section	Shows a slider with labels at major tick marks.
SliderDemo2	This section	Shows a vertical slider with custom labels.
Converter and other files	The Anatomy of a Swing-Based Program	Classes used by the Converter example, which features two sliders that share data and have a custom BoundedRangeModel.

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