JSlider Class

Package: javax.swing

The JSlider class creates a slider control, which lets a user pick a value from a set range (say, from 0 to 50) by moving a knob. A slider is a convenient way to get numeric input from the user when the input falls within a set range of values. Figure 5-10 shows a typical slider.

Figure 5-10

Constructors

Constructor	Description
JSlider()	Creates a new slider. The minimum and maximum values default to 0 and 100, and the initial value is set to 50.
JSlider(int min, int max)	Creates a new slider with the specified minimum and maximum values. The initial value is halfway between the minimum and maximum.
JSlider(int min, int max, int value)	Creates a new slider with the specified minimum, maximum, and initial values.
JSlider(int orientation, int min, int max, int value)	Creates a new slider with the specified minimum, maximum, and initial values. The orientation can be JSlider.HORIZONTAL or JSlider.VERTICAL.

Methods

Method	Description
void addChangeListener(ChangeListener listener)	Adds a ChangeListener to listen for change events.
int getValue()	Gets the value indicated by the current position of the knob.
void setFont()	Sets the font of the text associated with the slider.
void setInvert(boolean value)	If true, inverts the slider’s direction so that the maximum value is on the left and the minimum value is on the right.
void setMajorTick Spacing(int value)	Sets the interval for major tick marks. The marks aren’t shown unless setPaintTicks(true) is called.
void setMinimum(int value)	Sets the minimum value.
void setMaximum(int value)	Sets the maximum value.
void setMinorTick Spacing(int value)	Sets the interval for minor tick marks. The marks aren’t shown unless setPaintTicks(true) is called.
setOrientation(int orientation)	Sets the orientation. Allowed values are JSlider.HORIZONTAL and JSlider.VERTICAL.
void setPaintLabels(boolean value)	If true, shows tick labels.
void setSnapToTicks(boolean value)	If true, rounds the value returned by the getValue method to the nearest tick mark.
void setToolTipText	Sets the tooltip text that’s displayed if the user (String text) rests the mouse pointer over the slider for a few moments.

To create a bare-bones slider with default settings (range from 0 to 100, initial value of 50), just call the JSlider constructor:

slider = new JSlider();

If you want to specify the minimum and maximum values, use this constructor:

slider = new JSlider(0, 50);

The slider lets the user choose a value from 0 to 50. The initial position of the knob is 25, midway between the minimum and maximum values.

To set a different initial value, use this constructor:

slider = new JSlider(0, 0, 50);

Here, the slider ranges from 0 to 50, and the initial value is 0.

You usually want to add at least some adornments to the slider to make it more usable. The slider shown in Figure 5-10 has minimum and maximum tick-mark values with labels visible. Here’s the code used to create it:

slider = new JSlider(0, 50, 0);

slider.setMajorTickSpacing(10);

slider.setMinorTickSpacing(1);

slider.setPaintTicks(true);

slider.setPaintLabels(true);

panel1.add(slider);

Even if you set the major and minor tick-spacing values, the tick marks won’t appear onscreen unless you call setPaintTicks with the parameter set to true. The setPaintLabels method shows the labels along with the tick marks, and the setSnapToTicks method rounds the value to the nearest tick mark.

To get the value of the slider, you use the getValue method. Here’s the actionPerformed method for the action listener attached to the OK button in Figure 5-10:

public void actionPerformed(ActionEvent e)

{

if (e.getSource() == buttonOK)

{

int level = slider.getValue();

JOptionPane.showMessageDialog(slider,

“Remember, this is for posterity. ”

+ “Tell me...how do you feel?”,

“Level “ + level,

JOptionPane.INFORMATION_MESSAGE);

}

}

Here, a message box is displayed when the user clicks the OK button. The current setting of the slider component is retrieved and stored in an int variable named level, which is then used to create the title for the message box.