In this specific case, you should remove the elements in descending order. First index 5, then 3, then 1. This will remove the elements from the list without undesirable side effects. for (int j = i.length-1; j >= 0; j–) { list.remove(i[j]); }
list.toString() is good enough. The interface List does not define a contract for toString(), but the AbstractCollection base class provides a useful implementation that ArrayList inherits.
Cast works where the actual instance of the list is an ArrayList. If it is, say, a Vector (which is another extension of List) it will throw a ClassCastException. The error when changing the definition of your HashMap is due to the elements later being processed, and that process expects a method that is defined … Read more
ArrayList is unique in its naming standards. Here are the equivalencies: Array.push -> ArrayList.add(Object o); // Append the list Array.pop -> ArrayList.remove(int index); // Remove list[index] Array.shift -> ArrayList.remove(0); // Remove first element Array.unshift -> ArrayList.add(int index, Object o); // Prepend the list Note that unshift does not remove an element, but instead adds one … Read more
Since this is actually not a list of strings, the easiest way is to loop over it and convert each item into a new list of strings yourself: List<String> strings = list.stream() .map(object -> Objects.toString(object, null)) .toList(); Or when you’re not on Java 16 yet: List<String> strings = list.stream() .map(object -> Objects.toString(object, null)) .collect(Collectors.toList()); Or … Read more
You need to do it through an ArrayAdapter which will adapt your ArrayList (or any other collection) to your items in your layout (ListView, Spinner etc.). This is what the Android developer guide says: A ListAdapter that manages a ListView backed by an array of arbitrary objects. By default this class expects that the provided … Read more
Yes, because that’s not how you remove a range from outside code. Instead, do this: list.subList(start, end).clear(); This actually calls removeRange behind the scenes.† The OP asks why removeRange is not part of the List public API. The reason is described in Item 40 of Effective Java 2nd ed, and I quote it here: There … Read more
Yes it is safe to convert an ArrayList to an Array. Whether it is a good idea depends on your intended use. Do you need the operations that ArrayList provides? If so, keep it an ArrayList. Else convert away! ArrayList<Integer> foo = new ArrayList<Integer>(); foo.add(1); foo.add(1); foo.add(2); foo.add(3); foo.add(5); Integer[] bar = foo.toArray(new Integer[foo.size()]); System.out.println(“bar.length … Read more
Use Collections.synchronizedList(). Ex: Collections.synchronizedList(new ArrayList<YourClassNameHere>())
anyItem is a method and the System.out.println call is after your return statement so that won’t compile anyway since it is unreachable. Might want to re-write it like: import java.util.ArrayList; import java.util.Random; public class Catalogue { private Random randomGenerator; private ArrayList<Item> catalogue; public Catalogue() { catalogue = new ArrayList<Item>(); randomGenerator = new Random(); } public … Read more