question: public void testNumericScalars ( ) throws Exception { ObjectMapper m = new ObjectMapper ( ) ; m . enableDefaultTyping ( ) ; assertEquals ( "[123]" , m . writeValueAsString ( new Object [ ] { Integer . valueOf ( 123 ) } ) ) ; assertEquals ( "[[\"java.lang.Long\",37]]" , m . writeValueAsString ( new Object [ ] { Long . valueOf ( 37 ) } ) ) ; assertEquals ( "[0.25]" , m . writeValueAsString ( new Object [ ] { Double . valueOf ( 0.25 ) } ) ) ; assertEquals ( "[[\"java.lang.Float\",0.5]]" , m . writeValueAsString ( new Object [ ] { Float . valueOf ( 0.5f ) } ) ) ; }
target:  Unit test to verify that limited number of core types do NOT include type information, even if declared as Object. This is only done for types that JSON scalar values natively map to: String, Integer and Boolean (and nulls never have type information)