As Robert noted, this can be condensed to one using sorted, but that will do the same as the two lines above. Is there any direct way to do so? If time efficiency matters use a HashSet if space efficiency matters, look at TreeSet. A thing moderately good is not so good as it ought to be. As we have seen in , In Java, equals and hashcode method are an integral part of storing and retrieving object from it. Elements can be inserted and deleted using positions and duplicate elements are allowed in the list. Can I somehow avoid doing this in two stages? As pointed out: you already know how to create a set from an object; creating a list from an object is very similar: list set aa But why are you doing that? Doesn't do anything with the new set object, which will soon be garbage-collected.
The example was to show that after having made a set set aa the need to get that set converted into a list. Note that more efficient implementations of Set and Map are available through Trove and other locations. Though I'm a bit surprised consistency is not mentioned as a factor, as it is with , for example. Almost always, null is an error. That'a all about how to convert Map to List in Java. If you're after sorting, then consider the TreeSet. Can I somehow avoid first creating a long list only to immediately sort it afterwards? Can I somehow avoid doing this in two stages? By using copy constructor of Collection itself you can easily convert this Collection of Map values into List.
One additional note here is that hashing isn't guaranteed to be the same from run to run. If we want to get a HashSet then we can use the other alternative to get a set check set3. Thomas Rachel I'm not sure about if it is really the smartest way. If you know , you can easily convert this Set of keys into List of keys. As I mentioned in my answer, you could use a tree set to get a stable ordering. It's Java representation of popular hash table data structure which allows you to search an existing element in O 1 time, at the same time also makes insertion and removal easier. Thus: You cannot avoid creating these lists at all, the lists will have to be created.
You can also read by Cay S. Just like keys, Map also provides a Set view of all entries. Map to List in Java Here is our sample program to convert a Map to List in Java. If you like to know more about data structure provided by Java in Collection framework, see. There are multiple implementation of List is available in Java e. What are you trying to achieve? In 3rd example, we will see how to convert all entries of HashMap into List.
Map is an Interface in Java which store key and value object. Nobody asked how to convert null to a Set. Map allows you to get a view of all keys of Map as Set because duplicate keys are not permitted. Another option would be to use a LinkedHashSet which remembers the order that items were added to it. Another method to do what? There was something confusing me yesterday in doing that, but for me strangely I got cleared out. Especially when it's a null reference to a Collection: how often can you imagine a semantic meaning of a null refererence to a Collection - and such that the meaning is different from an empty Collection? My knowledge drove me to use a comprehension list as a converter.
Your example has exactly one assignment statement; all the other statements create objects which are never bound to anything. Sorry, some time we expect to have said it as we thought it. This example is divided into three parts; In first part we have converted keys of HashMap into List. The Map interface also provides three collection views, which allow a map's contents to be viewed as a set of keys, collection of values, or set of key-value mappings. In this case, duplication is identified using the. A short article focused on the common problem of testing if two List instances contain the same elements in exactly the same order. Evaluates the object referenced by the name? Ashish: This is completely irrelevant to the question.
Here is also a hierarchical diagram of Java Collection framework, you can see Map is not a subclass or subinterface of Collection, they are from the sepearte hierarchy. If you want to bind? Similar to earlier example, we can also store all entries into List. Thanks for any guidance, Mack MackS wrote: Dear all, I've got several large sets in my program. Just replace HashSet with TreeSet. What are you trying to achieve? This is done in combination with the. Horstmann to learn more about different collection classes in Java.
I'm not sure about if it is really the smartest way. The reason you are unable to save it in the Preferences even after converting it into a list is that you are trying to save StringList prefs. It's not a copy of the set, it's another reference to the same set; change one and you'll see the change in the other. Now let's understand what is a List in Java, It is also an interface to provide an ordered collection based on index. Is there any direct way to do so? Before making this change, keep in mind that there are fundamental differences between lists and sets. Does nothing with the new list object, which will soon be garbage-collected.