How do I clone a generic List in Java?
Why would you want to clone? Creating a new list usually makes more sense. List<String> strs; … List<String> newStrs = new ArrayList<>(strs); Job done.
arraylist
Get specific ArrayList item
As many have already told you: mainList.get(3); Be sure to check the ArrayList Javadoc. Also, be careful with the arrays indices: in Java, the first element is at index 0. So if you are trying to get the third element, your solution would be mainList.get(2);
How to split() a delimited string to a List
string.Split() returns an array – you can convert it to a list using ToList(): listStrLineElements = line.Split(‘,’).ToList(); Note that you need to import System.Linq to access the .ToList() function.
Check if a value exists in ArrayList
Just use ArrayList.contains(desiredElement). For example, if you’re looking for the conta1 account from your example, you could use something like: if (lista.contains(conta1)) { System.out.println(“Account found”); } else { System.out.println(“Account not found”); } Edit: Note that in order for this to work, you will need to properly override the equals() and hashCode() methods. If you are … Read more
How to efficiently remove all null elements from a ArrayList or String Array?
Try: tourists.removeAll(Collections.singleton(null)); Read the Java API. The code will throw java.lang.UnsupportedOperationException for immutable lists (such as created with Arrays.asList); see this answer for more details.
How can I create an Array of ArrayLists?
As per Oracle Documentation: “You cannot create arrays of parameterized types” Instead, you could do: ArrayList<ArrayList<Individual>> group = new ArrayList<ArrayList<Individual>>(4); As suggested by Tom Hawting – tackline, it is even better to do: List<List<Individual>> group = new ArrayList<List<Individual>>(4);
make arrayList.toArray() return more specific types
Like this: List<String> list = new ArrayList<String>(); String[] a = list.toArray(new String[0]); Before Java6 it was recommended to write: String[] a = list.toArray(new String[list.size()]); because the internal implementation would realloc a properly sized array anyway so you were better doing it upfront. Since Java6 the empty array is preferred, see .toArray(new MyClass[0]) or .toArray(new MyClass[myList.size()])? … Read more
How to sort an ArrayList in Java [duplicate]
Use a Comparator like this: List<Fruit> fruits= new ArrayList<Fruit>(); Fruit fruit; for(int i = 0; i < 100; i++) { fruit = new Fruit(); fruit.setname(…); fruits.add(fruit); } // Sorting Collections.sort(fruits, new Comparator<Fruit>() { @Override public int compare(Fruit fruit2, Fruit fruit1) { return fruit1.fruitName.compareTo(fruit2.fruitName); } }); Now your fruits list is sorted based on fruitName.
How to count the number of occurrences of an element in a List
I’m pretty sure the static frequency-method in Collections would come in handy here: int occurrences = Collections.frequency(animals, “bat”); That’s how I’d do it anyway. I’m pretty sure this is jdk 1.6 straight up.
How to declare an ArrayList with values? [duplicate]
In Java 9+ you can do: var x = List.of(“xyz”, “abc”); // ‘var’ works only for local variables Java 8 using Stream: Stream.of(“xyz”, “abc”).collect(Collectors.toList()); And of course, you can create a new object using the constructor that accepts a Collection: List<String> x = new ArrayList<>(Arrays.asList(“xyz”, “abc”)); Tip: The docs contains very useful information that usually … Read more