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

Long meetings (6-7 hours a day): Being “babysat” by supervisor

Image
Clash Royale CLAN TAG #URR8PPP .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty margin-bottom:0; up vote 31 down vote favorite 4 I hold a PhD in mechanical engineering with a 7 year background in self-guided, self-paced research including 2 years as a graduate level course instructor and a subject matter expert for various engineering projects in a university setting in the United States. For the last 10-11 months, I am working in a research industry in France where my task is to debug C++ spaghetti code written over a period of several years by my current supervisor. It is a team of 2: just I and my supervisor. Diurnally, I am posed with a "bug of the day" to get out of this C++ code. My supervisor generally gives me about 15-30 minutes to solve it and then accosts me about whether or not the task is completed and then rinses and repeats this until the end of the day. Off-late, my supervisor has been holding 6-7 hour long "meetin
Read more

What does second last employer means? [closed]

Image
Clash Royale CLAN TAG #URR8PPP .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty margin-bottom:0; up vote -3 down vote favorite Say, for example I have worked in the following companies, Company A => 2010 - 2011 Company B => 2011 - 2012 Company C => 2012 - Till Date Company D => Have offer Now assume Company D is asking to submit documents from my second last employer. So from the list of companies given, which company would be qualified as second last employer? software-industry employer share | improve this question asked Aug 10 '14 at 5:16 Rajaprabhu Aravindasamy 559 1 6 13 closed as off-topic by Jim G., jmort253 ♦ Aug 11 '14 at 1:58 This question appears to be off-topic. The users who voted to close gave this specific reason: "Questions seeking advice on company-specific regulations, agreements, or policies should be directed to your manager or HR department. Questions that address only
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