Summary

JComponent's setMinimumSize and setMaximumSize are overridden in JScrollBar to specify that JScrollBar's getMinimumSize and getMaximumSize returns a size derived from the preferred size in one axis and fixed value in the other axis.

Problem

The javadoc for JComponent.setMinimumSize(java.awt.Dimension) states:

"Sets the minimum size of this component to a constant value. Subsequent calls to getMinimumSize will always return this value..."

However, JScrollBar overrides getMinimumSize() and breaks this contract.

The returned Dimension is composed of the preferred width and a fixed minimum height, or vice versa depending on the orientation of the scrollbar.

Similarly, JScrollBar.getMaximumSize() uses the preferred width or height and a fixed maximum for the other dimension.

There's risk that changing this might cause the layout of applications to change in a way that breaks the applications. That change should have been made a long time ago.

Solution

JScrollBar's setMinimumSize() and setMaximumSize() are overridden to clarify the spec

Specification

javax.swing.JComponent.setMaximumSize

     /**
      * Sets the maximum size of this component to a constant
-     * value.  Subsequent calls to <code>getMaximumSize</code> will always
+     * value.  Subsequent calls to {@code getMaximumSize} will always
      * return this value; the component's UI will not be asked
-     * to compute it.  Setting the maximum size to <code>null</code>
+     * to compute it. Setting the maximum size to {@code null}
      * restores the default behavior.
+     * <p>
+     * Subclasses may choose to override this by returning their own maximum size
+     * in the {@code getMaximumSize} method.
      *
      * @param maximumSize a <code>Dimension</code> containing the
      *          desired maximum allowable size
      * @see #getMaximumSize
      */
     public void setMaximumSize(Dimension maximumSize) {

javax.swing.JComponent.setMinimumSize

     /**
      * Sets the minimum size of this component to a constant
-     * value.  Subsequent calls to <code>getMinimumSize</code> will always
+     * value.  Subsequent calls to {@code getMinimumSize} will always
      * return this value; the component's UI will not be asked
-     * to compute it.  Setting the minimum size to <code>null</code>
+     * to compute it. Setting the minimum size to {@code null}
      * restores the default behavior.
+     * <p>
+     * Subclasses may choose to override this by returning their own minimum size
+     * in the {@code getMinimumSize} method.
      *
      * @param minimumSize the new minimum size of this component
      * @see #getMinimumSize
      */
     public void setMinimumSize(Dimension minimumSize) {

javax.swing.JScrollBar.setMinimumSize

+    /**
+     * Unlike most components, {@code JScrollBar} derives the minimum size from
+     * the preferred size in one axis and a fixed minimum size in the other.
+     * Thus, it overrides {@code JComponent.setMinimumSize} contract
+     * that subsequent calls to {@code getMinimumSize} will return the
+     * same value as set in {@code JComponent.setMinimumSize}.
+     *
+     * @param minimumSize the new minimum size of this component
+     */
+    public void setMinimumSize(Dimension minimumSize) {

javax.swing.JScrollBar.setMaximumSize

     /**
+     * Unlike most components, {@code JScrollBar} derives the maximum size from
+     * the preferred size in one axis and a fixed maximum size in the other.
+     * Thus, it overrides {@code JComponent.setMaximumSize} contract
+     * that subsequent calls to {@code getMaximumSize} will return the
+     * same value as set in {@code JComponent.setMaximumSize}.
+     *
+     * @param maximumSize the desired maximum allowable size
+     */
+    public void setMaximumSize(Dimension maximumSize) {

javax.swing.JScrollBar.getMinimumSize

     /**
-     * The scrollbar is flexible along it's scrolling axis and
+     * Returns the minimum size for the {@code JScrollBar}.
+     * The scrollbar is flexible along its scrolling axis and
      * rigid along the other axis.
+     * As specified in {@code setMinimumSize} JScrollBar will derive the
+     * minimum size from the preferred size in one axis and a
+     * fixed minimum size in the other.
+     *
+     * @return the minimum size as specified above
      */
     public Dimension getMinimumSize() {

javax.swing.JScrollBar.getMaximumSize

     /**
-     * The scrollbar is flexible along it's scrolling axis and
+     * Returns the maximum size for the {@code JScrollBar}.
+     * The scrollbar is flexible along its scrolling axis and
      * rigid along the other axis.
+     * As specified in {@code setMaximumSize} JScrollBar will derive the
+     * maximum size from the preferred size in one axis and a
+     * fixed maximum size in the other.
+     *
+     * @return the maximum size as specified above
      */
     public Dimension getMaximumSize() {