question: public boolean validate ( ) { outputFile = new File ( outputPath ) ; if ( outputFile . exists ( ) || outputFile . isDirectory ( ) ) { invalidMessage = "Output file already exists." ; return valid = false ; } if ( ! signMode ) { keyFile = new File ( keyFilePath ) ; if ( ! keyFile . exists ( ) || keyFile . isDirectory ( ) ) { invalidMessage = "Key file not found." ; return valid = false ; } } return valid = true ; }
target:  Initialises and checks validity of files.  This objects toString() method changes to reflect failures in validation in order for the user to be informed.