Nice solution, I'll remember that in future. How does a Java HashMap handle different objects with the same hash Connect and share knowledge within a single location that is structured and easy to search. A dirty and a simple solution, if you use the maps just for sorting lets say, is to add a very small value to a key until the value does not exist, but do not add the minimum (for example Double.MIN_VALUE) because it will cause a bug. To learn more, see our tips on writing great answers. https://github.com/megamattron/collections-generic, I'm still going suggest the 2 map solution, but with a tweest. Is there a way to avoid this such that they point to the exact same value? If you want to associate a group of keys with the same object, it can be achieved by using a mutable object as a value. What are the pros and cons of allowing keywords to be abbreviated? Find centralized, trusted content and collaborate around the technologies you use most. Advantages: It is simple, enforces type safety, and doesn't store repeated data (as the two maps solutions do, though still store duplicate values). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Sounds like you might be a little confused about the difference between keys and hashed keys. HashMap with multiple values under the same key. Connect and share knowledge within a single location that is structured and easy to search. Two maps. Making statements based on opinion; back them up with references or personal experience. 2011-08-12T20:17:46.384Z, Overvoltage protection with ultra low leakage current for 3.3 V. Why are lights very bright in most passenger trains, especially at night? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. How can we compare expressive power between two Turing-complete languages? I need to avoid adding the same value twice. Can map have 2 same keys? 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 we have multiple values for same key in HashMap? i think the way to go is using a index decorator (see the key1, key2 examples above) and if the extra index key's are properties of the stored value you can use the property name's and reflection to build the secondairy maps when you put(key, val) and add an extra method get(propertyname, propertyvalue) to use that index. (Let's not be too general, let's say two keys). I have multiple files which contains key=value string pairs. Java: Multiple keys, one value HashMap, pointing to the exact same Is there a viable generic alternative to apache.commons.collections.CollectionUtils? I'll write a quick example (because I know this seems a little confusing when I try to explain it in writing.) Why is it better to control a vertical/horizontal than diagonal? But sometimes you may want to store multiple values for the same key. @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. which collection is the best way to get value from list which contains key value in android. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. I've just fixed it now. how to give credit for a picture I modified from a scientific article? It also lets you update the value through any key without the maps getting out of sync. Rust smart contracts? HashMap doesn't allow duplicate keys but allows duplicate values. how to add elements to arraylist and iterate, http://tomjefferys.blogspot.com.tr/2011/09/multimaps-google-guava.html. 1. How do you manage your own comments on a foreign codebase? In this way a single map can used for both keys. gdalwarp sum resampling algorithm double counting at some specific resolutions, Formulating P vs NP without Turing machines. HashMap in Java: What You Need to Know - History-Computer There is: org.springframework.util.MultiValueMap. Example: Then use your map as you normally would. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, @rowana you can create a new class holding two. I've tried this HashMap with multiple values under the same key, and my hashMap now looks like this HashMap> placeMap = new HashMap<>(); Also tried to put Object instead of Place(place is my superclass). But it has limitations: keys are ordered according to order of arguments in constructor and it would not work with 2D arrays, because of using Arrays.equals(). Difference between machine language and machine code, maybe in the C64 community? When did a PM last miss two, consecutive PMQs? @Jezor but this time using map structure wont be meaningful. Find centralized, trusted content and collaborate around the technologies you use most. Er, yeah, this is exactly what you proposed. The set supports element removal, which removes the corresponding mapping from . By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Should I sell stocks that are performing well or poorly first? Per @noahz's suggestion, forMap and invertFrom takes fewer lines, but is arguably more complex to read: If Java 8 is an option, you could try a streaming approach: As an interesting aside, I experimented with the time required for each algorithm when executing large maps of (index,random('a'-'z') pairs. 1. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. How could the Intel 4004 address 640 bytes if it was only 4-bit? Asking for help, clarification, or responding to other answers. Most efficient way to increment a Map value in Java. Example: The problem with Pair would be it's equality. (15 answers) Closed 6 years ago. Not the answer you're looking for? How do I open up this cable box, or remove it entirely? After reading in the keys, you can use String.intern(). You'd basically need a HashMap from a key to a collection of values. Find centralized, trusted content and collaborate around the technologies you use most. How do I generate random integers within a specific range in Java? Another nice choice is to use MultiValuedMap from Apache Commons. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. I need a data structure which behaves like a Map, Thanks for contributing an answer to Stack Overflow! It does still have close to the same memory usage as the two map approach in another answer, but might be more straight-forward. yes it working but it is showing data in [] formate i want those items one by one how to get that pls im stuck here, HashMap with multiple values under the same key. How can I make a Hashmap assign multiple values for a key? rev2023.7.3.43523. How can I sort Map values by key in Java? P.S. 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, HashMap with multiple values under the same key, Same values with different keys in a hashmap, Hashmaps having multiple keys with multiple values, Java HashMap, One key multiple Values, One map, Java: Multiple keys, one value HashMap, pointing to the exact same value, Is Linux swap still needed with Ubuntu 22.04, Options to insulate basement electric panel. You can do something like this (add access modifiers as required): This way each value for the key should have a unique identifier. For differently-typed keys I would use an Object? Is there any political terminology for the leaders who behave like the agents of a bigger power? This requires two look ups for every value access, which is a 100 % performance penalty. Stone-Weierstrass theorem for non-polynomials. Why schnorr signatures uses H(R||m) instead of H(m)? Can a HashMap have multiple values for same key? There needs to be only 1 single map and just a simple wrapper method that would put your keys and value into that map. @Deepak: Search for guava multimap examples and you'll find sample code. Safe to drive back home with torn ball joint boot? sol: cancatenate both keys and make a final key, use this as key. Actually, commons collections was forked to support generics, see this project here: How to implement a Map with multiple keys? Asking for help, clarification, or responding to other answers. Is the difference between additive groups and multiplicative groups just a matter of notation? a) Use 2 different maps. Should I sell stocks that are performing well or poorly first? Comparing Two HashMaps in Java | Baeldung I've created a HashMap like this: The String is the name of the Object, but the thing is that more than one object can have the same name. If you are open to using a library, use Google Guava's Multimaps utilities, specifically forMap() combined with invertFrom(). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How I can get the third value for the first key in this map? Difference between machine language and machine code, maybe in the C64 community? How could I do that here? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. A concise form would declare Map map Retrieval would be simple: map.get(someKeyForValue1), map.get(otherKeyForValue1) or map.contains(otherKeyForValue1). Sometimes generics just isn't worth the extra work. That said, if you still want to avoid duplicating the Strings, you can create the first HashMap, and then you the exact same keys for the other HashMaps. How link multiple keys to the same value in the HashMap Updating is a problem in my response as well. how to give credit for a picture I modified from a scientific article? I think this unswer is wrong. The only problem with this is if you dont have K1. Connect and share knowledge within a single location that is structured and easy to search. If you are using a hashmap there is no efficient way doing it but iterating the values. Thanks for contributing an answer to Stack Overflow! HashMap can be used to store key-value pairs. Is this possible? His statement says that keys are Unique, so saving the same value objects against different keys is quite possible and when you send any key matching the said value, we would be able to get back to the value object. Like I said, this is a very dirty solution but it makes the code simpler. Or you could create an entirely new object with the 2 keys as variables. One key object is associated with one value object. I don't know your specific usecase though. Is there an efficient way of checking if HashMap contains keys that map to the same value? Merge Two HashMaps Ignoring Duplicate Keys This one is a simple solution. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This is very simple and effective. Alright, will consider this.. java - How to implement a Map with multiple keys? - Stack Overflow

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