Perform operations add or remove on that list. Pass the same ArrayList to constructor of both Read and Write class constructor and initialize the list fields of both class. More on List representation of array link.The Write class will add elements to an ArrayList and another Read class will read elements from the same ArrayList.Ĭreate a list using an in the main() of the Sample class. Therefore, they will give error when trying to make some ArrayList operations listView_1.add(new Element(4)) // Error List listView_3 = Arrays.asList(new Element(1), new Element(2), new Element(3)) List listView_1 = (List) Arrays.asList(array) Returns a List view of array and not actual ArrayList Static List arrayToList(final T array) )) Īnd they very well support all operations of ArrayList arraylist_1.add(new Element(4)) // or remove(): SuccessĪrraylist_2.add(new Element(4)) // or remove(): SuccessĪrraylist_3.add(new Element(4)) // or remove(): Successīut the following operations returns just a List view of an ArrayList and not actual ArrayList. List l2b = new ArrayList(Arrays.asList("a", "b")) // Java 1.7+įor Educational Purposes: The Good ol' Manual Way // for Java 1.5+ List l2 = new ArrayList(Arrays.asList("a", "b")) // Java 1.5 to 1.6 List l1b = new ArrayList(Arrays.asList(array)) // Java 1.7+ Same as above, but wrapped with an actual : List l1 = new ArrayList(Arrays.asList(array)) // Java 1.5 to 1.6 See the next step if you need a mutable list. Thus this list isn't truly immutable and a call to asList() should be wrapped with Collections.unmodifiableList(). It forbids modifications through some of the List API's methods by way of simply extending an AbstractList (so, adding or removing elements is unsupported), however it allows calls to set() to override elements. It's an inner type, which emulates an ArrayList but actually directly references the passed array and makes it "write through" (modifications are reflected in the array). Note that the returned type for asList() is a List using a concrete ArrayList implementation, but it is NOT. List l2 = Collections.unmodifiableList(Arrays.asList("element1", "element2")) Use the JDK's Arrays class and its asList() factory method, wrapped with a Collections.unmodifiableList(): List l1 = Collections.unmodifiableList(Arrays.asList(anArrayOfElements)) You do in one Guava call what takes 2 with the current Java Collections. However, this argument holds less water since Java 7 arrived with the new diamond operator.īut it's not the only reason (and Java 7 isn't everywhere yet): the shorthand syntax is also very handy, and the methods initializers, as seen above, allow to write more expressive code. The main attraction could be to reduce the clutter due to generics for type-safety, as the use of the Guava factory methods allow the types to be inferred most of the time. Please also note the similar methods for other data structures in other classes, for instance in Sets. List l3 = Lists.newArrayList("or", "string", "elements") // from varargs List l2 = Lists.newArrayList(aStringArray) // from array Use the Lists class and its newArrayList() factory methods: List l1 = Lists.newArrayList(anotherListOrCollection) // from collection List il = pyOf(aStringArray) // from array Use the ImmutableList class and its of() and copyOf() factory methods (elements can't be null): List il = ImmutableList.of("string", "elements") // from varargs It's worth pointing out the Guava way, which greatly simplifies these shenanigans: Usage For an Immutable List (old thread, but just 2 cents as none mention Guava or other libs and some other details) If You Can, Use Guava
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