Java for arraylist remove

Class ArrayList

Type Parameters: E — the type of elements in this list All Implemented Interfaces: Serializable , Cloneable , Iterable , Collection , List , RandomAccess Direct Known Subclasses: AttributeList , RoleList , RoleUnresolvedList

Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null . In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to Vector , except that it is unsynchronized.)

The size , isEmpty , get , set , iterator , and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation.

Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.

An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation.

Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be «wrapped» using the Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:

List list = Collections.synchronizedList(new ArrayList(. ));

The iterators returned by this class’s iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods, the iterator will throw a ConcurrentModificationException . Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class is a member of the Java Collections Framework.

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Содержание

How To Use remove() Methods for Java List and ListArray
Java List remove() Methods
1. Remove the element at a given index
2. IndexOutOfBoundsException with remove(int index) Method
3. Unmodifiable List remove() UnsupportedOperationException Example
4. Removing an object from the list
Conclusion

How To Use remove() Methods for Java List and ListArray

Java List remove() method is used to remove elements from the list. ArrayList is the most widely used implementation of the List interface, so the examples here will use ArrayList remove() methods.

Java List remove() Methods

There are two remove() methods to remove elements from the List.

E remove(int index ) : This method removes the element at the specified index and returns it. The subsequent elements are shifted to the left by one place. This method throws IndexOutOfBoundsException if the specified index is out of range. If the list implementations does not support this operation, UnsupportedOperationException is thrown.
boolean remove(Object o ) This method removes the first occurrence of the specified Object . If the list doesn’t contain the given element, it remains unchanged. This method returns true if an element is removed from the list, otherwise false . If the object is null and list doesn’t support null elements, NullPointerException is thrown. UnsupportedOperationException is thrown if the list implementation doesn’t support this method.

Let’s look into some examples of remove() methods.

1. Remove the element at a given index

This example will explore E remove(int index ) :

ListString> list = new ArrayList>(); list.add("A"); list.add("B"); list.add("C"); list.add("C"); list.add("B"); list.add("A"); System.out.println(list); String removedStr = list.remove(1); System.out.println(list); System.out.println(removedStr);

First, this code constructs and prints a list:

Then, this code executes remove(1) to remove the element at index 1 . Finally, it prints the new resulting list and also prints the removed element.

The B at index 1 has been removed.

2. IndexOutOfBoundsException with remove(int index) Method

This example will explore E remove(int index ) when the index exceeds the list:

ListString> list = new ArrayList>(); list.add("A"); String removedStr = list.remove(10);

This code constructs a list with a length of 1 . However, when the code attempts to remove the element at index 10 :

Output
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 10 out of bounds for length 1 at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64) at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70) at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248) at java.base/java.util.Objects.checkIndex(Objects.java:372) at java.base/java.util.ArrayList.remove(ArrayList.java:535) at com.journaldev.java.ArrayListRemove.main(ArrayListRemove.java:19)

This attempt throws the IndexOutOfBoundsException .

3. Unmodifiable List remove() UnsupportedOperationException Example

The List.of() method creates an immutable list, which can’t be modified.

ListString> list = List.of("a", "b"); System.out.println(list); String removedStr = list.remove(1); System.out.println(removedStr);

First, this code constructs and prints an immutable list:

Then the code attempts to use the remove() method to remove the element at index 1 :

«main»

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$AbstractImmutableList

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)

This attempt throws UnsupportedOperationException . It will also throw UnsupportedOperationException if you attempt list.remove(«a») or list.remove(«b») .

4. Removing an object from the list

This example will explore boolean remove(Object o ) :

ListString> list = new ArrayList>(); list.add("A"); list.add("B"); list.add("C"); list.add("C"); list.add("B"); list.add("A"); System.out.println(list); boolean isRemoved = list.remove("C"); System.out.println(list); System.out.println(isRemoved); isRemoved = list.remove("X"); System.out.println(list); System.out.println(isRemoved);

First, this code constructs and prints a list:

Then, this code executes remove(«C») to remove the first instance of C . Next, it prints the resulting list and also prints the boolean value of the operation — true :

Then, this code executes remove(«X») , but there is no instance of X in the list, the list does not change. Finally, it prints the list and also prints the boolean value of the operation — false :

Conclusion

In this article, you learned about Java’s List method remove() .

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Class ArrayList

An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation.

List list = Collections.synchronizedList(new ArrayList(. ));

This class is a member of the Java Collections Framework.

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