why do two seemingly identical hashmaps have different behavior when serialized by gson?

The name of the pictureThe name of the pictureThe name of the pictureClash Royale CLAN TAG#URR8PPP











up vote
15
down vote

favorite












input:



public static void main(String args) 

 final String key = "some key";
 final String value = "some value";

 Map<String, String> map1 = new HashMap<String, String>()put(key, value);;
 System.out.println(new Gson().toJson(map1) + " " + map1.get(key));

 Map<String, String> map2 = new HashMap<>();
 map2.put(key, value);
 System.out.println(new Gson().toJson(map2) + " " + map2.get(key));



output:



null some value
"some key":"some value" some value

Process finished with exit code 0



java hashmap gson




share|improve this question


















  • 5




    Don't abuse "double brace initialization"...
    – user202729
    Aug 10 at 6:40










  • also related: stackoverflow.com/questions/1958636/…
    – Hulk
    Aug 10 at 9:36














up vote
15
down vote

favorite












input:



public static void main(String args) 

 final String key = "some key";
 final String value = "some value";

 Map<String, String> map1 = new HashMap<String, String>()put(key, value);;
 System.out.println(new Gson().toJson(map1) + " " + map1.get(key));

 Map<String, String> map2 = new HashMap<>();
 map2.put(key, value);
 System.out.println(new Gson().toJson(map2) + " " + map2.get(key));



output:



null some value
"some key":"some value" some value

Process finished with exit code 0



java hashmap gson




share|improve this question


















  • 5




    Don't abuse "double brace initialization"...
    – user202729
    Aug 10 at 6:40










  • also related: stackoverflow.com/questions/1958636/…
    – Hulk
    Aug 10 at 9:36












up vote
15
down vote

favorite









up vote
15
down vote

favorite











input:



public static void main(String args) 

 final String key = "some key";
 final String value = "some value";

 Map<String, String> map1 = new HashMap<String, String>()put(key, value);;
 System.out.println(new Gson().toJson(map1) + " " + map1.get(key));

 Map<String, String> map2 = new HashMap<>();
 map2.put(key, value);
 System.out.println(new Gson().toJson(map2) + " " + map2.get(key));



output:



null some value
"some key":"some value" some value

Process finished with exit code 0



java hashmap gson




share|improve this question














input:



public static void main(String args) 

 final String key = "some key";
 final String value = "some value";

 Map<String, String> map1 = new HashMap<String, String>()put(key, value);;
 System.out.println(new Gson().toJson(map1) + " " + map1.get(key));

 Map<String, String> map2 = new HashMap<>();
 map2.put(key, value);
 System.out.println(new Gson().toJson(map2) + " " + map2.get(key));



output:



null some value
"some key":"some value" some value

Process finished with exit code 0




java hashmap gson





share|improve this question













share|improve this question




share|improve this question








edited Aug 10 at 4:21









Iłya Bursov

17.6k32443




17.6k32443










asked Aug 10 at 4:18









dQw4w9WyXcQ

784




784







  • 5




    Don't abuse "double brace initialization"...
    – user202729
    Aug 10 at 6:40










  • also related: stackoverflow.com/questions/1958636/…
    – Hulk
    Aug 10 at 9:36












  • 5




    Don't abuse "double brace initialization"...
    – user202729
    Aug 10 at 6:40










  • also related: stackoverflow.com/questions/1958636/…
    – Hulk
    Aug 10 at 9:36







5




5




Don't abuse "double brace initialization"...
– user202729
Aug 10 at 6:40




Don't abuse "double brace initialization"...
– user202729
Aug 10 at 6:40












also related: stackoverflow.com/questions/1958636/…
– Hulk
Aug 10 at 9:36




also related: stackoverflow.com/questions/1958636/…
– Hulk
Aug 10 at 9:36












1 Answer
1






active

oldest

votes

















up vote
21
down vote



accepted










For map1, you have created an anonymous subclass. Assuming your class that contains main() is called ExampleClass, then:



System.out.println(map1.getClass().getName())


prints out:



ExampleClass$1


Whereas printing the class for map2 yields:



java.util.HashMap


As to the exact reason that Gson doesn't serialise it - Gson uses the classname to lookup a converter. If you instead serialise it using:



System.out.println(new Gson().toJson(map1, HashMap.class));


... it works as expected.






share|improve this answer
















  • 1




    Relevant documentation.
    – VGR
    Aug 10 at 4:35










Your Answer





StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
convertImagesToLinks: true,
noModals: false,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);













 

draft saved


draft discarded


















StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f51778907%2fwhy-do-two-seemingly-identical-hashmaps-have-different-behavior-when-serialized%23new-answer', 'question_page');

);

Post as a guest

















1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
21
down vote



accepted










For map1, you have created an anonymous subclass. Assuming your class that contains main() is called ExampleClass, then:



System.out.println(map1.getClass().getName())


prints out:



ExampleClass$1


Whereas printing the class for map2 yields:



java.util.HashMap


As to the exact reason that Gson doesn't serialise it - Gson uses the classname to lookup a converter. If you instead serialise it using:



System.out.println(new Gson().toJson(map1, HashMap.class));


... it works as expected.






share|improve this answer
















  • 1




    Relevant documentation.
    – VGR
    Aug 10 at 4:35














up vote
21
down vote



accepted










For map1, you have created an anonymous subclass. Assuming your class that contains main() is called ExampleClass, then:



System.out.println(map1.getClass().getName())


prints out:



ExampleClass$1


Whereas printing the class for map2 yields:



java.util.HashMap


As to the exact reason that Gson doesn't serialise it - Gson uses the classname to lookup a converter. If you instead serialise it using:



System.out.println(new Gson().toJson(map1, HashMap.class));


... it works as expected.






share|improve this answer
















  • 1




    Relevant documentation.
    – VGR
    Aug 10 at 4:35












up vote
21
down vote



accepted







up vote
21
down vote



accepted






For map1, you have created an anonymous subclass. Assuming your class that contains main() is called ExampleClass, then:



System.out.println(map1.getClass().getName())


prints out:



ExampleClass$1


Whereas printing the class for map2 yields:



java.util.HashMap


As to the exact reason that Gson doesn't serialise it - Gson uses the classname to lookup a converter. If you instead serialise it using:



System.out.println(new Gson().toJson(map1, HashMap.class));


... it works as expected.






share|improve this answer












For map1, you have created an anonymous subclass. Assuming your class that contains main() is called ExampleClass, then:



System.out.println(map1.getClass().getName())


prints out:



ExampleClass$1


Whereas printing the class for map2 yields:



java.util.HashMap


As to the exact reason that Gson doesn't serialise it - Gson uses the classname to lookup a converter. If you instead serialise it using:



System.out.println(new Gson().toJson(map1, HashMap.class));


... it works as expected.







share|improve this answer












share|improve this answer



share|improve this answer










answered Aug 10 at 4:34









Greg Kopff

10.5k53762




10.5k53762







  • 1




    Relevant documentation.
    – VGR
    Aug 10 at 4:35












  • 1




    Relevant documentation.
    – VGR
    Aug 10 at 4:35







1




1




Relevant documentation.
– VGR
Aug 10 at 4:35




Relevant documentation.
– VGR
Aug 10 at 4:35

















 

draft saved


draft discarded















































 


draft saved


draft discarded














StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f51778907%2fwhy-do-two-seemingly-identical-hashmaps-have-different-behavior-when-serialized%23new-answer', 'question_page');

);

Post as a guest
































































Comments

Post a Comment

Popular posts from this blog

White Anglo-Saxon Protestant

Image
White Anglo-Saxon Protestants ( WASPs ) are a social group of wealthy and well-connected white Americans, of Protestant and predominantly British ancestry, who trace their ancestry to the American colonial period. Until at least the 1960s, this group has dominated American society and culture and dominated in the leadership of the Whig and Republican parties. They usually are very well placed in major financial, business, legal and academic institutions and had close to a monopoly of elite society due to intermarriage and nepotism. [1] During the latter half of the twentieth century, outsider ethnic and racial groups grew in influence and WASP dominance weakened. Americans are increasingly criticizing the WASP hegemony and disparaging WASPs as the epitome of "the Establishment". The Random House Unabridged Dictionary (1998) says the term is "Sometimes Disparaging and Offensive". [2] [3] The term WASP is often used as a pejorative to classify their historical dom...
Read more

Is the Concept of Multiple Fantasy Races Scientifically Flawed? [closed]

Image
Clash Royale CLAN TAG #URR8PPP up vote 2 down vote favorite Many fantasy worlds have multiple humanoid species (elves, orcs, humans, etc) living in the same world, in addition to that, they often have the ability to interbreed. And I can't help but question their believability... fantasy-races reproduction interspecies-relations share | improve this question edited Aug 9 at 14:46 Michael Kjörling ♦ 21.1k 10 85 161 asked Aug 9 at 13:13 Chlodio 118 6 closed as unclear what you're asking by MichaelK, Gryphon, John, Vincent, Frostfyre Aug 9 at 15:25 Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question. ...
Read more

One-line joke

A one-liner is a joke that is delivered in a single line. A good one-liner is said to be pithy - concise and meaningful. [1] Comedians and actors use this comedic method as part of their act, e.g. Jimmy Carr, Tommy Cooper, Rodney Dangerfield, Norm Macdonald, Ken Dodd, Stewart Francis, Zach Galifianakis, Mitch Hedberg, Anthony Jeselnik, Milton Jones, Shappi Khorsandi, Jay London, Mark Linn-Baker, Demetri Martin, Groucho Marx, Dan Mintz, Emo Philips, Tim Vine, Steven Wright and Henny Youngman and Arnold Schwarzenegger. [ citation needed ] Many fictional characters are also known to deliver one-liners, including James Bond, who usually includes pithy and laconic quips after disposing of a villain. [ citation needed ] Examples "A baby seal walks into a club." "A dyslexic man walks into a bra." (Anonymous) "There are three types of people, those who can count and those who can't." "Venison's dear, isn't it?" (Jimmy Carr) "An escala...
Read more