final Dimension cpMinConstraint = splitPane.getMinimumSize();// target min constraint of content pane

final double frameHeightDelta = frame.getSize().getHeight() - frame.getContentPane().getSize().getHeight();
final double frameWidthDelta = frame.getSize().getWidth() - frame.getContentPane().getSize().getWidth();
messagesArea.requestFocusInWindow();
final Dimension frameMinConstraint = new Dimension();
final double width = cpMinConstraint.getWidth() + frameWidthDelta;
final double height = cpMinConstraint.getHeight() + frameHeightDelta;
frameMinConstraint.setSize( width, height );
frame.setMinimumSize( frameMinConstraint );// applying target cp min constraint to JFrame