Java generic collections are not stored with a type to ensure backwards compatibility with pre J2SE 5.0. Type information is removed when added to a generic collection. This is called Type Erasure. This means that a generic collection can be assigned to a non generic reference and objects in a generic typed collection can be … Read more
In Java, creating an array of a generic type is not straightforward. The simple approach does not compile: public class Container<E> { E[] arr = new E[3]; // ERROR: Cannot create a generic array of E } Replace E with Object, and all is well (at the expense of added complexity elsewhere in the container … Read more
Try this It worked for me 1st Activity ArrayList<String> ar=new ArrayList<String>(); ar.add(“Apple”); ar.add(“Banana”); Intent i=new Intent(this,Route.class); i.putStringArrayListExtra(“list”, ar); startActivity(i); 2nd Activity ArrayList<String> ar1=getIntent().getExtras().getStringArrayList(“list”);
Source : Here You can use Collections.sort with a custom Comparator<Team>. class Team { public final int points; // … }; List<Team> players = // … Collections.sort(players, new Comparator<Team>() { @Override public int compare(Team p1, Team p2) { return p1.points- p2.points; } }); Alternatively, you can make Team implementsComparable<Team>. This defines the natural ordering for … Read more
You can create a list of lists public class MultiDimList: List<List<string>> { } or a Dictionary of key-accessible Lists public class MultiDimDictList: Dictionary<string, List<int>> { } MultiDimDictList myDicList = new MultiDimDictList (); myDicList.Add(“ages”, new List<int>()); myDicList.Add(“Salaries”, new List<int>()); myDicList.Add(“AccountIds”, new List<int>()); Generic versions, to implement suggestion in comment from @user420667 public class MultiDimList<T>: List<List<T>> { … Read more
When calculating the average time to insert into a vector, you need to allow for the non-growing inserts and the growing inserts. Call the total number of operations to insert n items ototal, and the average oaverage. If you insert n items, and you grow by a factor of A as required, then there are … Read more
You can’t assign a List<Number> to a reference of type List<Integer> because List<Number> allows types of numbers other than Integer. If you were allowed to do that, the following would be allowed: List<Number> numbers = new ArrayList<Number>(); numbers.add(1.1); // add a double List<Integer> ints = numbers; Integer fail = ints.get(0); // ClassCastException! The type List<Integer> … Read more
You can’t, within the enhanced for loop. You have to use the “long-hand” approach: for (Iterator<Pixel> iterator = pixels.iterator(); iterator.hasNext(); ) { Pixel px = iterator.next(); if(px.y > gHeigh){ iterator.remove(); } } Of course, not all iterators support removal, but you should be fine with ArrayList. An alternative is to build an additional collection of … Read more
You can’t. This is normally done with dynamic memory allocation. // Like “ENEMY enemies[100]”, but from the heap ENEMY* enemies = malloc(100 * sizeof(ENEMY)); if (!enemies) { error handling } // You can index pointers just like arrays. enemies[0] = CreateEnemy(); // Make the array bigger ENEMY* more_enemies = realloc(enemies, 200 * sizeof(ENEMY)); if (!more_enemies) … Read more
The list being synchronized only means that add, remove etc. operations are synchronized and therefore atomic. Iteration however is not and if a thread adds while another is iterating, you could get a ConcurrentModificationException. By manually synchronizing your iteration block, you ensure that the list is not modified while iterating. One alternative is to use … Read more