You don’t need to synchronize as you put in your example. HOWEVER, very important, you need to synchronize around the list when you iterate it (as noted in the Javadoc): It is imperative that the user manually synchronize on the returned list when iterating over it: List list = Collections.synchronizedList(new ArrayList()); … synchronized(list) { Iterator … Read more
Using Java 8 and if you prefer not to instantiate a List instance by yourself, like in the suggested (and accepted) solution someMap.values().forEach(someList::addAll); You could do it all by streaming with this statement: List<String> someList = map.values().stream().flatMap(c -> c.stream()).collect(Collectors.toList()); By the way it should be interesting to know, that on Java 8 the accepted version … Read more
Jon Bentley discusses this in either ‘Programming Pearls’ or ‘More Programming Pearls’. You need to be careful with your N of M selection process, but I think the code shown works correctly. Rather than randomly shuffle all the items, you can do the random shuffle only shuffling the first N positions – which is a … Read more
As Matthieu says, the only case where you wouldn’t want to set inverse = true is where it does not make sense for the child to be responsible for updating itself, such as in the case where the child has no knowledge of its parent. Lets try a real world, and not at all contrived … Read more
Suppose we could. Then this program would have to be fine: ArrayList<Banana> bananas = new ArrayList<Banana>(); List<Fruit> fruit = bananas; fruit.add(new Apple()); Banana banana = bananas.get(0); That’s clearly not type safe – you’ve ended up with an apple in the collection of bananas. What you can do is: List<? extends Fruit> fruit = new ArrayList<Banana>(); … Read more
In addition to the functional solutions provided (using the static methods on the Enumerable class), you can pass an array of doubles in the constructor. var tenDoubles = new List<double>(new double[10]); This works because the default value of an double is already 0, and probably performs slightly better.
list.groupBy(_.property).map(_._2.head) Explanation: The groupBy method accepts a function that converts an element to a key for grouping. _.property is just shorthand for elem: Object => elem.property (the compiler generates a unique name, something like x$1). So now we have a map Map[Property, List[Object]]. A Map[K,V] extends Traversable[(K,V)]. So it can be traversed like a list, … Read more
That line creates an empty list of strings by calling a static method with a generic type parameter. Inside the Collections class, there is a static method emptyList declared like: public static final <T> List<T> emptyList() { return (List<T>) EMPTY_LIST; } This has a generic type parameter T. We call call this method by using: … Read more
With OData 4.01, in statement is supported like this: http://host/service/Products?$filter=Name in (‘Milk’, ‘Cheese’)
It runs in O(1) expected time, as any hash table (assuming the hash function is decent). It is backed by a HashMap where the key is the Object. Two objects might have the same hash code, but the HashSet wouldn’t think they are identical, unless the equals method for these objects says they are the … Read more