Download Java Remove
Mathilde Chisler
The use of the remove method can be found more often in the Java Collection framework. The remove method removes the specified element from any collection of objects. However, the ways to remove an object might differ in one case or the other.
We know that ArrayList allows the insertion of duplicate objects. So, if the same object is present at multiple positions, the above remove method will remove its first occurrence only.
Alternatively, if the index is passed as a parameter, the remove method will remove and return the removed element as well. However, if the index is not in the range of the ArrayList, the remove method throws IndexOutOfBoundsException.
When we pass an object to the remove method, it has to iterate through every element in the list until it finds out the one needed for removal. And obviously, the remaining elements on the right also need to be shifted.So, the overall time complexity is O(N).
The remove method in Java has varied uses in the Collection interface. Although the operation is to simply remove an object from a collection of objects, it has several variants where the parameters, as well as the return values, differ.
In our discussion, we'll be primarily focusing on the use of the remove method in ArrayList. Also, the use of the remove method in Set, Maps and Queues has been demonstrated in the end.
The remove() method is implemented in the other interfaces too, including Set, Queue, Maps, etc. Let us take a quick look at some of the examples related to each one of these interfaces where the remove() method is used.Since Set, Queue, Maps are interfaces, we'll need a class that implements these interfaces to create objects.
HashMap uses Hash Table as its data structure. The remove method in HashMap consumes O(1) time. The put method also has O(1) time complexity. So, the overall time complexity will be O(1).
Note that iterator.remove() will not work as far as I can see because I need to remove multiple things at a time. Also assume that it is not possible to identify which elements to remove "on the fly", but it is possible to write the method setOfElementsToRemove(). In my specific case it would take up a lot of memory and processing time to determine what to remove while iterating. Making copies is also not possible because of memory constraints.
Normally when you remove an element from a collection while looping over the collection, you'll get a Concurrent Modification Exception. This is partially why the Iterator interface has a remove() method. Using an iterator is the only safe way to modify a collection of elements while traversing them.
Instead of iterating through all the elements in the Set to remove the ones you want, you can actually use Google Collections (not something you can't do it on your own though) and apply a Predicate to mask the ones you don't need.
Any solution that involves removing from the set you're iterating while you're iterating it, but not via the iterator, will absolutely not work. Except possibly one: you could use a Collections.newSetFromMap(new ConcurrentHashMap(sizing params)). The catch is that now your iterator is only weakly consistent, meaning that each time you remove an element that you haven't encountered yet, it's undefined whether that element will show up later in your iteration or not. If that's not a problem, this might work for you.
Another thing you can do is build up a toRemove set as you go instead, then set.removeAll(itemsToRemove); only at the end. Or, copy the set before you start, so you can iterate one copy while removing from the other.
You could try the java.util.concurrent.CopyOnWriteArraySet which gives you an iterator that is a snapshot of the set at the time of the iterator creation. Any changes you make to the set (i.e. by calling removeAll()) won't be visible in the iterator, but are visible if you look at the set itself (and removeAll() won't throw).
Also note, that on most java.util collections the remove method will generate exception if the contents of the collection have changed. So, if the code is multi-threaded use extra caution, or use concurrent collections.
Unlike sets, lists typically allow duplicate elements. More formally, lists typically allow pairs of elements e1 and e2 such that e1.equals(e2), and they typically allow multiple null elements if they allow null elements at all. It is not inconceivable that someone might wish to implement a list that prohibits duplicates, by throwing runtime exceptions when the user attempts to insert them, but we expect this usage to be rare. The List interface places additional stipulations, beyond those specified in the Collection interface, on the contracts of the iterator, add, remove, equals, and hashCode methods. Declarations for other inherited methods are also included here for convenience. The List interface provides four methods for positional (indexed) access to list elements. Lists (like Java arrays) are zero based. Note that these operations may execute in time proportional to the index value for some implementations (the LinkedList class, for example). Thus, iterating over the elements in a list is typically preferable to indexing through it if the caller does not know the implementation. The List interface provides a special iterator, called a ListIterator, that allows element insertion and replacement, and bidirectional access in addition to the normal operations that the Iterator interface provides. A method is provided to obtain a list iterator that starts at a specified position in the list. The List interface provides two methods to search for a specified object. From a performance standpoint, these methods should be used with caution. In many implementations they will perform costly linear searches. The List interface provides two methods to efficiently insert and remove multiple elements at an arbitrary point in the list. Note: While it is permissible for lists to contain themselves as elements, extreme caution is advised: the equals and hashCode methods are no longer well defined on such a list. Some list implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException or ClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the list may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface. This interface is a member of the Java Collections Framework.Since:1.2See Also:Collection, Set, ArrayList, LinkedList, Vector, Arrays.asList(Object[]), Collections.nCopies(int, Object), Collections.EMPTY_LIST, AbstractList, AbstractSequentialListMethod SummaryAll Methods Instance Methods Abstract Methods Default Methods Modifier and TypeMethod and Descriptionbooleanadd(E e)Appends the specified element to the end of this list (optional operation).voidadd(int index, E element)Inserts the specified element at the specified position in this list (optional operation).booleanaddAll(Collection
Hello i have been recently tasked with a plan and execute the removal of java from all systems in our environment. The previous person was attempting to complete this through a series of task Sequences in SCCM but was not very successful. Are there any scripts to complete this task and should it be completed by task sequence?
I can't recall what I did wrong but i have a folder named "usr/lib/java/jdk/1.8.0_45"that has a desktop for itself in it and all that, basicly an user for itself and all my pictures get saved in there and sometimes it messes with my downloads but I can't remove it in system settings/users. So could somebody please help me on removing it.
The technologies were maintained by upstream projects on java.net and later on GitHub. This made maintenance problematic due to having to sync the Java SE versions in OpenJDK repositories with the Java EE versions in upstream repositories.
The javax.transaction.xa package supports XA transactions in JDBC. This "XA package" is co-located with JDBC in the java.sql module in Java SE 9. Because the java.sql module is not upgradeable, it is not possible for a standalone version of JTA to override the Java SE version of the XA package, but this is generally acceptable to applications because the XA package has been stable for many years and the Java SE version is identical to the Java EE version. For ease of maintenance, the XA package in Java SE may be moved to a different non-upgradeable module in the future, but as an architectural matter it will remain in Java SE alongside JDBC for the long term, and is of no further interest to this JEP.
The javax.transaction package defines a general transaction management API. The Java EE version of this package was always beyond the scope of Java SE and has evolved in ways that are not relevant to Java SE. For example, JTA added types in Java EE 7 that concern CDI. The subset of javax.transaction defined by Java SE supports interoperation with CORBA transaction services. This "CORBA interop package" exists in its own java.transaction module in Java SE 9. However, the Java SE version is generally not acceptable to applications that use CORBA transaction services, so they usually override it with the Java EE version.
The J2EE Activity Service defines a generic middleware API. It has not been updated since 2006 and is not part of the Java EE Platform. It is relevant to this JEP only because Java SE includes a subset of one of its packages, javax.activity, for interoperation with CORBA transaction services. This "activity package" exists in the java.corba module in Java SE 9.
df19127ead