question: private void writeObject ( ObjectOutputStream stream ) throws IOException , ClassNotFoundException { ObjectOutputStream . PutField fields = stream . putFields ( ) ; fields . put ( "positivePrefix" , ndf . getPositivePrefix ( ) ) ; fields . put ( "positiveSuffix" , ndf . getPositiveSuffix ( ) ) ; fields . put ( "negativePrefix" , ndf . getNegativePrefix ( ) ) ; fields . put ( "negativeSuffix" , ndf . getNegativeSuffix ( ) ) ; fields . put ( "posPrefixPattern" , ( String ) null ) ; fields . put ( "posSuffixPattern" , ( String ) null ) ; fields . put ( "negPrefixPattern" , ( String ) null ) ; fields . put ( "negSuffixPattern" , ( String ) null ) ; fields . put ( "multiplier" , ndf . getMultiplier ( ) ) ; fields . put ( "groupingSize" , ( byte ) ndf . getGroupingSize ( ) ) ; fields . put ( "groupingUsed" , ndf . isGroupingUsed ( ) ) ; fields . put ( "decimalSeparatorAlwaysShown" , ndf . isDecimalSeparatorAlwaysShown ( ) ) ; fields . put ( "parseBigDecimal" , ndf . isParseBigDecimal ( ) ) ; fields . put ( "roundingMode" , roundingMode ) ; fields . put ( "symbols" , symbols ) ; fields . put ( "useExponentialNotation" , false ) ; fields . put ( "minExponentDigits" , ( byte ) 0 ) ; fields . put ( "maximumIntegerDigits" , ndf . getMaximumIntegerDigits ( ) ) ; fields . put ( "minimumIntegerDigits" , ndf . getMinimumIntegerDigits ( ) ) ; fields . put ( "maximumFractionDigits" , ndf . getMaximumFractionDigits ( ) ) ; fields . put ( "minimumFractionDigits" , ndf . getMinimumFractionDigits ( ) ) ; fields . put ( "serialVersionOnStream" , 4 ) ; stream . writeFields ( ) ; }
target:  Writes serialized fields following serialized forms specified by Java specification.