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.
- How to add Integer Values to ArrayList, int array Examples
- 1. Introduction
- 2. Adding primitive int values to ArrayList
- 3. Adding Integer Wrapper Objects to List
- 4. ArrayList of int array in java
- 5. Conclusion
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- Конструкторы ArrayList
- Методы ArrayList
- Ссылки на дополнительное чтение
How to add Integer Values to ArrayList, int array Examples
A quick guide on how to add int or integer values to ArrayList using add() method. ArrayList of int array in java.
1. Introduction
In this tutorial, We’ll learn an ArrayList problem of how to add integer values to an ArrayList. Let us write an example program to add primitive int values and wrapper integer objects.
In the previous articles, we have discussed how to remove duplicate values in ArrayList.
In the next article, We’ll learn How to Iterate ArrayList values?
2. Adding primitive int values to ArrayList
Let us write a sample program to add primitive int values to List. Take a look at the below program that List object is created as new ArrayList and assigned the reference to List .
package com.java.w3schools.blog.arraylist; import java.util.ArrayList; import java.util.List; /** * * Adding primitive int to ArrayList * * @author javaprogramto.com * */ public class ArrayListAddPrimitiveIntGenerics < public static void main(String[] args) < Listl = new ArrayList (); l.add(100); l.add(200); l.add(309); > >
When compile this program generates a compile-time error.
Exception in thread "main" java.lang.Error: Unresolved compilation problems: Syntax error, insert "Dimensions" to complete ReferenceType Syntax error, insert "Dimensions" to complete ReferenceType at com.java.w3schools.blog.arraylist.ArrayListAddPrimitiveIntGenerics.main(ArrayListAddPrimitiveIntGenerics.java:17)
import java.util.ArrayList; import java.util.List; /** * * Adding primitive int to ArrayList * * @author javaprogramto.com * */ public class ArrayListAddPrimitiveInt < public static void main(String[] args) < List l = new ArrayList(); l.add(10); l.add(20); l.add(30); l.add(40); l.add(50); l.add(60); System.out.println("primitive list values : " + l); >> ArrayList object l in the program will accept any type of values but here we are adding only primitive type int values.
primitive list values : [10, 20, 30, 40, 50, 60]
3. Adding Integer Wrapper Objects to List
In this program, an example is shown with generics by specifying the type of values that Arraylist accepts. List indicates that it takes only Integer objects.
But, in the code passed only primitives. Let us compile the code and see the output.
public class ArrayListAddPrimitiveIntegers < public static void main(String[] args) < Listl = new ArrayList<>(); l.add(1); l.add(2); l.add(3); l.add(4); l.add(5); System.out.println("wrapper integers list values : " + l); > >
This program compiles and runs without any issues.
wrapper integers list values : [1, 2, 3, 4, 5]
Because java JVM does the autoboxing that converts primitive to boxed object.
4. ArrayList of int array in java
public class ArrayListAddPrimitiveIntegersArray < public static void main(String[] args) < Listlist = new ArrayList<>(); // int[] intArray = < 1, 2, 3, 4, 5, 6, 7, 8, 9 >; Integer[] intArray = < 1, 2, 3, 4, 5, 6, 7, 8, 9 >; list.add(0, intArray); System.out.println("int array to arraylsit : " + list); > >
int array to arraylsit : [[Ljava.lang.Integer;@4e25154f]
To see the values inside the int[] array, we need to iterate over int[] array.
Printing the values inside int[] array of ArrayList (ArrayList
5. Conclusion
In this short article, we have seen how to add int values to ArrayList and also adding int array to List.
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A quick guide on how to add int or integer values to ArrayList using add() method. ArrayList of int array in java.
ArrayList в Java
ArrayList — реализация изменяемого массива интерфейса List, часть Collection Framework, который отвечает за список (или динамический массив), расположенный в пакете java.utils. Этот класс реализует все необязательные операции со списком и предоставляет методы управления размером массива, который используется для хранения списка. В основе ArrayList лежит идея динамического массива. А именно, возможность добавлять и удалять элементы, при этом будет увеличиваться или уменьшаться по мере необходимости.
Что хранит ArrayList?
Только ссылочные типы, любые объекты, включая сторонние классы. Строки, потоки вывода, другие коллекции. Для хранения примитивных типов данных используются классы-обертки.
Конструкторы ArrayList
ArrayList list = new ArrayList<>(); ArrayList list2 = new ArrayList<>(list); ArrayList list2 = new ArrayList<>(10000); Методы ArrayList
Ниже представлены основные методы ArrayList.
ArrayList list = new ArrayList<>(); list.add("Hello"); ArrayList secondList = new ArrayList<>(); secondList.addAll(list); System.out.println("Первое добавление: " + secondList); secondList.addAll(1, list); System.out.println("Второе добавление в середину: " + secondList); Первое добавление: [Amigo, Hello] Второе добавление в середину: [Amigo, Amigo, Hello, Hello] ArrayList copyOfSecondList = (ArrayList) secondList.clone(); secondList.clear(); System.out.println(copyOfSecondList); System.out.println(copyOfSecondList.contains("Hello")); System.out.println(copyOfSecondList.contains("Check")); // Первый способ for(int i = 0; i < secondList.size(); i++) < System.out.println(secondList.get(i)); >И цикл for-each: // Второй способ for(String s : secondList)
В классе ArrayList есть метод для обработки каждого элемента, который называется также, forEach. В качестве аргумента передается реализация интерфейса Consumer, в котором нужно переопределить метод accept():
secondList.forEach(new Consumer() < @Override public void accept(String s) < System.out.println(s); >>); Метод accept принимает в качестве аргумента очередной элемент того типа, который хранит в себе ArrayList. Пример для Integer:
ArrayList integerList = new ArrayList<>(); integerList.forEach(new Consumer() < @Override public void accept(Integer integer) < System.out.println(integer); >>); String[] array = new String[secondList.size()]; secondList.toArray(array); for(int i = 0; i
Ссылки на дополнительное чтение
- Подробная статья о динамических массивах, а точнее — об ArrayList и LinkedList , которые выполняют их роль в языке Java.
- Статья об удалении элементов из списка ArrayList.
- Лекция о работе с ArrayList в схемах и картинках.