sliderV = new JSlider( SwingConstants.VERTICAL,  
    0, 1000, 400);
sliderV.setMajorTickSpacing( 100 );
sliderV.setMinorTickSpacing(  50 );
sliderV.setPaintTicks ( true );
sliderV.setPaintLabels( true ); 

setPreferredSize()

The layout managers have control over the size of components, but often do their job better if you indicate a preferred size. This is done with

setPreferredSize( new Dimension( int width, int height )

If this is not used, the graphical representation of a slider often has its labels and tick marks crowded together.

sliderV.setPreferredSize( new Dimension( ____, ____) );