{"id":358861,"date":"2024-05-21T00:20:35","date_gmt":"2024-05-21T00:20:35","guid":{"rendered":"http:\/\/savepearlharbor.com\/?p=358861"},"modified":"-0001-11-30T00:00:00","modified_gmt":"2024-05-21T00:20:35","slug":"","status":"publish","type":"post","link":"https:\/\/savepearlharbor.com\/?p=358861","title":{"rendered":"List in Java | Interface, Methods, Example<\/span>"},"content":{"rendered":"
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In this topic, we will learn about what is a\u00a0List in Java<\/em>. How to create a List in Java? What are the methods of List in Java? The List is an interface in Java. It is extending the Collection interface in Java. This List interface is present in the\u00a0java.util\u00a0<\/strong>package in Java. A list represents a group of individual objects as a single entity where duplicates are allowed and insertion order is preserved.<\/p>\n

public interface List<E> extends Collection<E><\/code><\/pre>\n
\u2192 In the above, we mentioned the general declaration of the List in Java.<\/p>\n
How to create a List in Java?<\/h3>\n
The list interface has four concrete subclasses(ArrayList, LinkedList, Vector and Stack) in the Collection Framework.
We can create the list by using its concrete subclasses as follows:<\/p>\n
List l1 = new ArrayList(); List l2 = new LinkedList(); List l3 = new Vector(); List l4= new Stack();<\/code><\/pre>\n
How to create a Generic List object in Java?<\/h3>\n
We can create the generic list object as follows:<\/p>\n
List<data type> list = new ArrayList<data type>(); <\/code><\/pre>\n
\u2192 In the above, we mentioned the general syntax of creating a\u00a0generic<\/strong><\/a>\u00a0List by using the ArrayList class.<\/p>\n
List<String> list = new ArrayList<String>();<\/code><\/pre>\n
\u2192 In the above create a list of objects of String type by using ArrayList class.<\/p>\n
List<Integer> list = new LinkedList<Integer>();<\/code><\/pre>\n
\u2192 In the above example, we created a list of objects of Integer type by using the LinkedList class.\u00a0 \u00a0<\/p>\n
List<String> list = new LinkedList<String>();<\/code><\/pre>\n
\u2192 In the above example, we created a list of objects of String type by using the LinkedList class.<\/p>\n
List<User> list=new ArrayList<User>(); <\/code><\/pre>\n
\u2192 In the above example, we created a list of objects of type obj by using the ArrayList class. The User\u00a0is the type object.<\/p>\n
 List<String> strList = new ArrayList<>();  List<Integer> list = new LinkedList<>();<\/code><\/pre>\n
\u2192 Java 1.7 onwards, we can use a diamond operator<\/p>\n
What are the Methods of List?<\/h3>\n
The List interface has several methods:\u00a0
\u00a0\u00a0\u2022 void add(int index, E element):\u00a0<\/strong>This method is used to insert an object at a particular position in the list.
\u00a0 \u00a0 \u00a0\u00a0E<\/strong>— It is a type of element in the list
For example, suppose we want to add \u201cPeter\u201d at the 4th position in the list we can use this method as below:<\/p>\n
list.add(4,\"Peter\");<\/code><\/pre>\n
\u00a0 \u2022\u00a0boolean addAll(int index, Collection<? extends E> c):<\/strong>\u00a0This method is used to add a Collection object at the particular position in the list and shift the subsequent objects to the right by increasing their indices.
For example, suppose we want to add a list at the 2nd position in the other list we can use this method as below:<\/p>\n
list.add(\"P\"); list.add(\"Q\"); list.add(\"R\");<\/code><\/pre>\n
Now, we will create a new list using list1 reference.<\/p>\n
list1.add(\"W\"); list1.add(\"Y\");<\/code><\/pre>\n
Now, we will add list1 at the 2nd position in the list.<\/p>\n
list.add(2,list2);<\/code><\/pre>\n
\u00a0\u00a0\u2022 E remove(int index):<\/strong>\u00a0This method is used to remove an element at a specified position in the list.
For example, we consider the following:<\/p>\n
list.remove(2);<\/code><\/pre>\n
\u00a0 \u2022 E get(int index):<\/strong>\u00a0This method is used to return an object stored at a specified position in the list.
For example, we consider the following:<\/p>\n
list.get(1);<\/code><\/pre>\n
\u00a0\u00a0\u2022 E set(int index, E element):\u00a0<\/strong>This method is used to replace an existing element with a new element with a specified position in the list.
For example, we consider the following:<\/p>\n
list.set(1, \"T\");<\/code><\/pre>\n
\u00a0\u00a0\u2022 int indexOf(Object o):<\/strong>\u00a0This method is used to return an index of the particular element of the first occurrence in the list. If the specified element is not present in the list then will return -1.
For example, we consider the following:<\/p>\n
list.indexOf(\"A\");<\/code><\/pre>\n
\u00a0\u00a0\u2022 int lastIndexOf(Object o):\u00a0<\/strong>This method is used to return an index of the particular element of the last occurrence in the list. If the specified element is not present in the list then will return -1.
For example, we consider the following:<\/p>\n
list.lastIndexOf(\"A\");<\/code><\/pre>\n
\u00a0\u00a0\u2022 ListIterator<E> listIterator():<\/strong>\u00a0This method is used to return the listIterator of the elements in the list in a proper sequence.
\u00a0\u00a0\u2022 ListIterator<E> listIterator(int index):\u00a0<\/strong>This method is used to return a listIterator of the elements in the list in the proper sequence, starting at the specified position in the list.<\/p>\n
Example of Create a List in Java<\/h3>\n
import java.util.ArrayList;  import java.util.List;  public class Test {  public static void main(String[] args){  List<String> al = new ArrayList<String>(); al.add(\"Apple\");  al.add(\"Mango\");  al.add(\"Orange\");  al.add(\"Grapes\");  System.out.println(\"List1 contains: \" +al);  List<String> al2 = new ArrayList<String>();  al2.add(\"10\");  al2.add(\"11\");  al2.add(\"12\");  System.out.println(\"List2 contains : \"+al2);  al.addAll(2, al2);  System.out.println(\"After added List2 at 2nd index in the list: \" +al);    }  }<\/code><\/pre>\n
Output<\/strong><\/p>\n
List1 contains: [Apple, Mango, Orange, Grapes] List2 contains : [10, 11, 12] List1 after adding List2 at 2nd index: [Apple, Mango, 10, 11, 12, Orange, Grapes]<\/code><\/pre>\n
How to Iterate List in Java?<\/h3>\n
There are different ways to iterate a list in Java. You can refer to the post by\u00a0clicking here<\/strong><\/a>.\u00a0<\/p>\n
When to use List in Java?<\/h3>\n
There are the following points where we will use List:
\u00a0 \u2022 When we want to need duplicate elements to store
\u00a0 \u2022 When we want to allow null elements
\u00a0 \u2022 When we want to preserve the insertion order<\/p>\n
Conclusion<\/h4>\n
In this topic, we learnt about\u00a0what is a List Interface in Java and its various methods<\/strong>.<\/p>\n<\/div>\n<\/div>\n<\/div>\n
<\/div>\n

 \u0441\u0441\u044b\u043b\u043a\u0430 \u043d\u0430 \u043e\u0440\u0438\u0433\u0438\u043d\u0430\u043b \u0441\u0442\u0430\u0442\u044c\u0438  https:\/\/habr.com\/ru\/articles\/770790\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
<\/div>\n
\n
\n
\n
\n
In this topic, we will learn about what is a\u00a0List in Java<\/em>. How to create a List in Java? What are the methods of List in Java? The List is an interface in Java. It is extending the Collection interface in Java. This List interface is present in the\u00a0java.util\u00a0<\/strong>package in Java. A list represents a group of individual objects as a single entity where duplicates are allowed and insertion order is preserved.<\/p>\n
public interface List<E> extends Collection<E><\/code><\/pre>\n
\u2192 In the above, we mentioned the general declaration of the List in Java.<\/p>\n
How to create a List in Java?<\/h3>\n
The list interface has four concrete subclasses(ArrayList, LinkedList, Vector and Stack) in the Collection Framework.
We can create the list by using its concrete subclasses as follows:<\/p>\n
List l1 = new ArrayList(); List l2 = new LinkedList(); List l3 = new Vector(); List l4= new Stack();<\/code><\/pre>\n
How to create a Generic List object in Java?<\/h3>\n
We can create the generic list object as follows:<\/p>\n
List<data type> list = new ArrayList<data type>(); <\/code><\/pre>\n
\u2192 In the above, we mentioned the general syntax of creating a\u00a0generic<\/strong><\/a>\u00a0List by using the ArrayList class.<\/p>\n
List<String> list = new ArrayList<String>();<\/code><\/pre>\n
\u2192 In the above create a list of objects of String type by using ArrayList class.<\/p>\n
List<Integer> list = new LinkedList<Integer>();<\/code><\/pre>\n
\u2192 In the above example, we created a list of objects of Integer type by using the LinkedList class.\u00a0 \u00a0<\/p>\n
List<String> list = new LinkedList<String>();<\/code><\/pre>\n
\u2192 In the above example, we created a list of objects of String type by using the LinkedList class.<\/p>\n
List<User> list=new ArrayList<User>(); <\/code><\/pre>\n
\u2192 In the above example, we created a list of objects of type obj by using the ArrayList class. The User\u00a0is the type object.<\/p>\n
 List<String> strList = new ArrayList<>();  List<Integer> list = new LinkedList<>();<\/code><\/pre>\n
\u2192 Java 1.7 onwards, we can use a diamond operator<\/p>\n
What are the Methods of List?<\/h3>\n
The List interface has several methods:\u00a0
\u00a0\u00a0\u2022 void add(int index, E element):\u00a0<\/strong>This method is used to insert an object at a particular position in the list.
\u00a0 \u00a0 \u00a0\u00a0E<\/strong>— It is a type of element in the list
For example, suppose we want to add \u201cPeter\u201d at the 4th position in the list we can use this method as below:<\/p>\n
list.add(4,\"Peter\");<\/code><\/pre>\n
\u00a0 \u2022\u00a0boolean addAll(int index, Collection<? extends E> c):<\/strong>\u00a0This method is used to add a Collection object at the particular position in the list and shift the subsequent objects to the right by increasing their indices.
For example, suppose we want to add a list at the 2nd position in the other list we can use this method as below:<\/p>\n
list.add(\"P\"); list.add(\"Q\"); list.add(\"R\");<\/code><\/pre>\n
Now, we will create a new list using list1 reference.<\/p>\n
list1.add(\"W\"); list1.add(\"Y\");<\/code><\/pre>\n
Now, we will add list1 at the 2nd position in the list.<\/p>\n
list.add(2,list2);<\/code><\/pre>\n
\u00a0\u00a0\u2022 E remove(int index):<\/strong>\u00a0This method is used to remove an element at a specified position in the list.
For example, we consider the following:<\/p>\n
list.remove(2);<\/code><\/pre>\n
\u00a0 \u2022 E get(int index):<\/strong>\u00a0This method is used to return an object stored at a specified position in the list.
For example, we consider the following:<\/p>\n
list.get(1);<\/code><\/pre>\n
\u00a0\u00a0\u2022 E set(int index, E element):\u00a0<\/strong>This method is used to replace an existing element with a new element with a specified position in the list.
For example, we consider the following:<\/p>\n
list.set(1, \"T\");<\/code><\/pre>\n
\u00a0\u00a0\u2022 int indexOf(Object o):<\/strong>\u00a0This method is used to return an index of the particular element of the first occurrence in the list. If the specified element is not present in the list then will return -1.
For example, we consider the following:<\/p>\n
list.indexOf(\"A\");<\/code><\/pre>\n
\u00a0\u00a0\u2022 int lastIndexOf(Object o):\u00a0<\/strong>This method is used to return an index of the particular element of the last occurrence in the list. If the specified element is not present in the list then will return -1.
For example, we consider the following:<\/p>\n
list.lastIndexOf(\"A\");<\/code><\/pre>\n
\u00a0\u00a0\u2022 ListIterator<E> listIterator():<\/strong>\u00a0This method is used to return the listIterator of the elements in the list in a proper sequence.
\u00a0\u00a0\u2022 ListIterator<E> listIterator(int index):\u00a0<\/strong>This method is used to return a listIterator of the elements in the list in the proper sequence, starting at the specified position in the list.<\/p>\n
Example of Create a List in Java<\/h3>\n
import java.util.ArrayList;  import java.util.List;  public class Test {  public static void main(String[] args){  List<String> al = new ArrayList<String>(); al.add(\"Apple\");  al.add(\"Mango\");  al.add(\"Orange\");  al.add(\"Grapes\");  System.out.println(\"List1 contains: \" +al);  List<String> al2 = new ArrayList<String>();  al2.add(\"10\");  al2.add(\"11\");  al2.add(\"12\");  System.out.println(\"List2 contains : \"+al2);  al.addAll(2, al2);  System.out.println(\"After added List2 at 2nd index in the list: \" +al);    }  }<\/code><\/pre>\n
Output<\/strong><\/p>\n
List1 contains: [Apple, Mango, Orange, Grapes] List2 contains : [10, 11, 12] List1 after adding List2 at 2nd index: [Apple, Mango, 10, 11, 12, Orange, Grapes]<\/code><\/pre>\n
How to Iterate List in Java?<\/h3>\n
There are different ways to iterate a list in Java. You can refer to the post by\u00a0clicking here<\/strong><\/a>.\u00a0<\/p>\n
When to use List in Java?<\/h3>\n
There are the following points where we will use List:
\u00a0 \u2022 When we want to need duplicate elements to store
\u00a0 \u2022 When we want to allow null elements
\u00a0 \u2022 When we want to preserve the insertion order<\/p>\n
Conclusion<\/h4>\n
In this topic, we learnt about\u00a0what is a List Interface in Java and its various methods<\/strong>.<\/p>\n<\/div>\n<\/div>\n<\/div>\n
<\/div>\n

 \u0441\u0441\u044b\u043b\u043a\u0430 \u043d\u0430 \u043e\u0440\u0438\u0433\u0438\u043d\u0430\u043b \u0441\u0442\u0430\u0442\u044c\u0438  https:\/\/habr.com\/ru\/articles\/770790\/<\/a>
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