e799. 限制JSlider的数值在标记以内

By default, the slider can take on any value from the minimum to the maximum. It is possible to configure the slider to allow only values at tick marks (see e797 显示JSlider的标记). This is done by calling JSlider.setSnapToTicks(true).

The slider's minimum and minor tick-mark spacing determines what values are possible. For example, if the minimum is 3 and the minor tick-mark spacing is 10, only the values, 3, 13, 23, and so forth, are allowed. If a minor tick-mark spacing has not been set, the major tick-mark spacing is used. If neither a minor nor a major tick mark spacing has been set, a tick-mark spacing of 1 is assumed.

Calling setSnapToTicks() also has the effect of causing the slider's knob to snap to the closest tick mark whenever it is dragged or programmatically moved to a spot between tick marks.

    // Create a horizontal slider that moves left-to-right
    JSlider slider = new JSlider();
    // Set major tick marks every 25 units
    int tickSpacing = 25;
    slider.setMajorTickSpacing(tickSpacing);
    
    // Set minor tick marks every 5 units
    tickSpacing = 5;
    slider.setMinorTickSpacing(tickSpacing);
    
    // Show tick marks
    slider.setPaintTicks(true);
    
    // Determine if currently snapping to tick marks
    boolean b = slider.getSnapToTicks(); // false
    
    // Snap to tick marks
    slider.setSnapToTicks(true);
    
    // Set to a spot between tick marks; the value moves to closest tick mark
    slider.setValue(27);
    int value = slider.getValue();  // 25

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