question: private boolean verifyDomainRangeLowerBoundInput ( JComponent input ) { JTextField textField = ( JTextField ) input ; String inputString = textField . getText ( ) ; try { double domainLowerBound ; if ( inputString . startsWith ( "-" ) ) { domainLowerBound = Double . parseDouble ( inputString . substring ( 1 ) ) ; domainLowerBound = - domainLowerBound ; } else { domainLowerBound = Double . parseDouble ( inputString ) ; } } catch ( NumberFormatException e ) { textField . setForeground ( Color . RED ) ; return false ; } textField . setForeground ( Color . BLACK ) ; return true ; }
target:  Verify that the y-value is correct.