I would advice EVERYONE against Apache Collections. It would be nice if I could do How it is then that the USA is so high in violent crime. Could you please comment on consistency of hashcode vs equals of your proposal b)? Some people suggest me to use a tuple, a pair, or similar as a key for How to take large amounts of money away from the party without causing player resentment? I need a data structure which behaves like a Map, rev2023.7.3.43523. Connect and share knowledge within a single location that is structured and easy to search. What is the equivalent of the C++ Pair in Java? How to link elements of two linked list in java? How do laws against computer intrusion handle the modern situation of devices routinely being under the de facto control of non-owners? Do large language models know what they are talking about? I would like to create a hashmap with 2 keys. How to resolve the ambiguity in the Boy or Girl paradox? Find centralized, trusted content and collaborate around the technologies you use most. Can we have multiple values for same key in HashMap? @MithunS If I'm understanding this answer correctly, the effect is that a given value will appear in the map twice (or more), once for each key that points to that value. Just as HashMap? What syntax could be used to implement both an exponentiation operator and XOR? But I'd probably try to iterate through map's entry set, check key part and then extract the other in the same loop. Java HashMap hierarchy HashMap extends AbstractMap and implements Map. HashMap: Multiple Values under one key - code2test: Testing site Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Any recommendation? Multiple indexes for a Java Collection - most basic solution? how to add elements to arraylist and iterate, http://tomjefferys.blogspot.com.tr/2011/09/multimaps-google-guava.html. If so, you can iterate through your ArrayList and get the item you like with arrayList.get(i). Yet another solution is to use Google's Guava. PI cutting 2/3 of stipend without notice. However, it may well be simpler to use a library than to roll your own, test it etc this solution would only work if the objects in the ArrayList are from the same type. Either you could do that by combining their .toString() or .hashCode(). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Cannot infer type arguments for Hashmap<>, It's giving error "Cannot infer type arguments for Hashmap<>". Rust smart contracts? How can I make a Hashmap assign multiple values for a key? So what I want to know is, what would be the best data structure to use if I need something like above, if that is not valid? See: http://google-collections.googlecode.com/svn/trunk/javadoc/index.html?com/google/common/collect/Multimap.html. @Deepak: I suggest you try creating an example yourself, and if you get stuck, ask a question including the code as far as you've got. 1. How does this work , when you want to lookup by just key1 ? Merging Two Maps with Java 8 | Baeldung I could not post a reply on Paul's comment so I am creating new comment for Vidhya here: Wrapper will be a SuperClass for the two classes which we want to store as a value. To learn more, see our tips on writing great answers. you store value "1" with K1=A and K2=B, then you store value "1" with K1=C and K2=D. I need to avoid adding the same value twice. Two Maps is the way to go. For instance, you can make use of StringBuilder or implement a custom class. hashcode seems consistent with equals to me in that any time two objects are equal their hashcodes will be equal. 586), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Testing native, sponsored banner ads on Stack Overflow (starting July 6), Temporary policy: Generative AI (e.g., ChatGPT) is banned. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Can I have a hash map in Java that looks like this? @Deepak: Basically you'd build something like. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Thanks friendsbut i have some limitations in using MultiHashMap. Hashtables - Same key many values? HashMap doesn't allow duplicate keys but allows duplicate values. Is there a finite abelian group which is not isomorphic to either the additive or multiplicative group of a field? Find centralized, trusted content and collaborate around the technologies you use most. It's simpler, more concise, and less abstract. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Drawbacks: Not generic. Hey, thanks for the feedback Laf, the only problem I get with this is the row, @FilipBlom YEah I made a typo. 1. http://insidecoffe.blogspot.de/2013/04/indexable-hashmap-implementation.html. I believe It could also be made generic by adding to the class definition, internally using Object (or better yet ?) The solution is to build a Wrapper clas for your values that contains the 2 (3, or more) values that correspond to your key. posted 13 years ago That's right. Initialization To start, we'll define two Map instances: gdalwarp sum resampling algorithm double counting at some specific resolutions. In this way a single map can used for both keys. A typed based registration would also allow you to retrieve the "correct" map to be used: although searching for the second key might not be efficient, Another possile solution providing the possibility of more complicated keys can be found here: http://insidecoffe.blogspot.de/2013/04/indexable-hashmap-implementation.html. Why did only Pinchas (knew how to) respond? Why can clocks not be compared unless they are meeting? how to give credit for a picture I modified from a scientific article? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. It will have same effect like same key and multiple values. When did a PM last miss two, consecutive PMQs? Instead of having Map think of Map or directly MultiMap from guava. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How do laws against computer intrusion handle the modern situation of devices routinely being under the de facto control of non-owners? Java - multiple hashmaps pointing to the same key - Stack Overflow It appears that I can use a Hashtable and plug objects into it using the same key? Java HashMap - learn how to use Java HashMap - ZetCode If not, is there any other way to implement the storage of multiple values e.g. Find centralized, trusted content and collaborate around the technologies you use most. I have to be able, as written above, to search values by only one of the two keys specified. That would be key1. Is there a finite abelian group which is not isomorphic to either the additive or multiplicative group of a field? Thank you for the suggestions. And then use it's objects as keys in your map: HashMap<MyKey, Integer> hmap = new HashMap<>() . Use firstMap.putAll (secondMap) method that copies all of the mappings from the secondMap to firstMap. EDIT First story to suggest some successor to steam power? To learn more, see our tips on writing great answers. 1. Like I said, this is a very dirty solution but it makes the code simpler. How can I specify different theory levels for different atoms in Gaussian? Do I need to create a HashCode method into my object class which shall create a unique hashcode? Connect and share knowledge within a single location that is structured and easy to search. Sounds like a Python tuple. For example: For Key A, you want to store - Apple, Aeroplane. Nathan Leniz Ranch Hand Posts: 132 posted 16 years ago I've got a couple questions I couldn't really discern. How to maximize the monthly 1:1 meeting with my boss? If you are open to using a library, use Google Guava's Multimaps utilities, specifically forMap() combined with invertFrom(). Maps use hash codes of keys and check for their equality. You'll have to write or find Pair<>; it's pretty easy but not part of the standard Collections. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I don't think you can do any better then just iterate. ? https://mvnrepository.com/artifact/com.google.collections/google-collections/1.0-rc2, http://tomjefferys.blogspot.be/2011/09/multimaps-google-guava.html, http://google-collections.googlecode.com/svn/trunk/javadoc/index.html?com/google/common/collect/Multimap.html, https://stackoverflow.com/a/44181931/8065321. Can a HashMap have multiple values for same key? In other words, this is not a class that will handle a variable number of keys is it? How can I add such "multiple" keys? To learn more, see our tips on writing great answers. First you have a map of all the possible synonyms to the same value e.g. Java Hashtable : one key - two value, how to get both of them? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. You always need to specify both key1 and key2. k.hashCode() * 17 + t.hashCode(). Hopefully this will set you straight: A Map can't have multiple values for one key, but you can have a Collection as value instead. Connect and share knowledge within a single location that is structured and easy to search. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Or should I create a HashMap where K is a certain word and V contains an arraylist of its sysnonyms, and then try to iterate over the ArrayList to compare the splitted user input with the elements in the ArrayList to extract the necessary key? Java: Multiple keys, one value HashMap, pointing to the exact same value. Eg. What is this date format? 586), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Testing native, sponsored banner ads on Stack Overflow (starting July 6), Temporary policy: Generative AI (e.g., ChatGPT) is banned, Reverse/inverse map with non unique values to multimap, How to print all the values for a key in HashMap in java, Identify the Key-Value pair having duplicate values, Evicting cache with multiple keys for the same value, Same values with different keys in a hashmap. Implementing a Map with Multiple Keys in Java | Baeldung This is Google-Guava library for utility functionalities. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. HashMap<String, String, Integer> hmap = new HashMap<String, String, Integer>() My question is similar to this one hereQuestion I'm a . retrieve all map keys having a same value. sol: cancatenate both keys and make a final key, use this as key. If you know any reason why it could not be used as a solution for such issues - please, let me know! By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. but uses multiple (differently-typed) keys to access its values. I am so used to just doing this with a Data Dictionary in Objective C. It was harder to get a similar result in Java for Android. Is it possible to implement a HashMap with one key and two values? A Java collection of value pairs? How could I do that here? Is the difference between additive groups and multiplicative groups just a matter of notation? HashMap allows null key also but only once and multiple null values. I don't think it would work one by one though.. He can just use a list. Do large language models know what they are talking about? What is the best way to visualise such data? Apart from all the answers here, I have a solution that I used and found it most useful if you know the length of multiple values to be added to your key. Then you can use it like: one key and two values? 2. Difference between machine language and machine code, maybe in the C64 community? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. If so, I'm having a bit of a problem and could use some help. Should I sell stocks that are performing well or poorly first? There is no way you can solve the initial problem with Commons-collections's MultiKeyMap class. Thinking about a Map with 2 keys immediately compelled me to use a user-defined key, and that would probably be a Class. This is probably getting a bit theoretical though, as it doesn't look like the original question takes updates into account.
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