hashset

What's the best way to convert HashSet<String> to String[] ? set.toArray(new String[set.size()]); Answer of JB Nizet is correct, but in case you did this to transform to a CSV like string, with Java 8 you can now do: Set<String> mySet = new HashSet<>(Arrays.asList("a", "b", "c")); System.out.println(String.join(", ", mySet)); Output is: a, b, c This allows to bypass arrays. 来源： https://stackoverflow.com/questions/5474656/converting-from-hashsetstring-to-string

I have been reading/researching the reason why HashMap is faster than HashSet . I am not quite understanding the following statements: HashMap is faster than HashSet because the values are associated to a unique key. In HashSet , member object is used for calculating hashcode value which can be same for two objects so equals() method is used to check for equality. If it returns false , that means the two objects are different. In HashMap , the hashcode value is calculated using the key object. The HashMap hashcode value is calculated using the key object. Here, the member object is used to

In some library code, I have a List that can contain 50,000 items or more. Callers of the library can invoke methods that result in strings being added to the list. How do I efficiently check for uniqueness of the strings being added? Currently, just before adding a string, I scan the entire list and compare each string to the to-be-added string. This starts showing scale problems above 10,000 items. I will benchmark this, but interested in insight. if I replace the List<> with a Dictionary<> , will ContainsKey() be appreciably faster as the list grows to 10,000 items and beyond? if I defer

With a list you can do: list.AddRange(otherCollection); There is no add range method in a HashSet . What is the best way to add another collection to a HashSet? quetzalcoatl For HashSet<T> , the name is UnionWith . This is to indicate the distinct way the HashSet works. You cannot safely Add a set of random elements to it like in Collections , some elements may naturally evaporate. I think that UnionWith takes its name after "merging with another HashSet ", however, there's an overload for IEnumerable<T> too. RoadieRich This is one way: public static class Extensions { public static bool

As an exercise I am developing a simple notes application. Obviously the notes have to be saved persistently so I have the following method: public static void saveNotesPersistently() { SharedPreferences.Editor editor = sharedPreferences.edit(); HashSet<String> titleSet = new HashSet<String>(); HashSet<String> contentSet = new HashSet<String>(); for (int i = 0; i < Library.notes.size(); i++) { String title = (Library.notes.get(i).title == null) ? "No title" : Library.notes.get(i).title; Log.d("Checks", "Saving note with title: " + title); String content = (Library.notes.get(i).content == null)