Interface List
An ordered collection (also known as a sequence). The user of this interface has precise control over where in the list each element is inserted. The user can access elements by their integer index (position in the list), and search for elements in the list.
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.
Unmodifiable Lists
- They are unmodifiable. Elements cannot be added, removed, or replaced. Calling any mutator method on the List will always cause UnsupportedOperationException to be thrown. However, if the contained elements are themselves mutable, this may cause the List’s contents to appear to change.
- They disallow null elements. Attempts to create them with null elements result in NullPointerException .
- They are serializable if all elements are serializable.
- The order of elements in the list is the same as the order of the provided arguments, or of the elements in the provided array.
- The lists and their subList views implement the RandomAccess interface.
- They are value-based. Programmers should treat instances that are equal as interchangeable and should not use them for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail. Callers should make no assumptions about the identity of the returned instances. Factories are free to create new instances or reuse existing ones.
- They are serialized as specified on the Serialized Form page.
This interface is a member of the Java Collections Framework.
Add ArrayList to another ArrayList in Java | addAll method
A quick guide to add one ArrayList values into Another using ArrayList constructor and using addAll() method.
In this post, We will learn How to add ArrayList into a another ArrayList in java.
We can accumulate this in two ways.
1) While creating ArrayList object.
2) Using addAll method.
1) Adding existing ArrayList into new list:
ArrayList has a constructor which takes list as input. Constructs a list containing the elements of the specified collection, in the order they are returned by the collection’s iterator.
package com.adeepdrive.arraylist; import java.util.ArrayList; import java.util.List; // Java - W3schools public class AddAnotherList < public static void main(String[] args) < // Creating ArryList - Existing Object ListexistingList = new ArrayList(); existingList.add("America"); existingList.add("New York"); existingList.add("Sidny"); System.out.println("Existing ArrayList Object : " + existingList); // Creating a new ArrayList by passing exiting ArrayList List newList = new ArrayList(existingList); // Printng the new List System.out.println("Newly created ArrayList Object : " + newList); > > Existing ArrayList Object : [America, New York, Sidny]
Newly created ArrayList Object : [America, New York, Sidny]
First created one ArrayList object as named existingList and added three values to them as America, New York, Sidny. Then printed values of existingList.
Next created another ArrayList object as newList by passing existing existingList and not added any values to it, just printed newList then we see the same values as existingList.
2. How to add using addAll method:
ArrayList has a method named addAll() which is very useful when we do not have access arraylist creation logic (creation implementation is in some jar — third party jar).
public boolean addAll(Collection c)
addAll Example program:
package com.adeepdrive.arraylist; import java.util.ArrayList; import java.util.List; // Java - W3schools public class AddAnotherListAddAll < public static void main(String[] args) < // gettingexisting Roles. List existingRoles = getExistingRoles(); // We have new roles in the list. List newUserRoles = new ArrayList(); newUserRoles.add("TimesheetApprove"); newUserRoles.add("LeaveApprove"); newUserRoles.add("CabApprove"); // We have to add new roles to the existing roles then we should go for addAll // method. System.out.println("Printing roles before adding new roles: "+existingRoles); existingRoles.addAll(newUserRoles); System.out.println("Printing roles after adding new roles: "+existingRoles); > // For understanding, I have created new method in the same class. In real time, // this method will be in some jar which is provided by other application // managed by different team. public static List getExistingRoles() < // Creating ArryList - Existing Object ListexistingRoles = new ArrayList(); existingRoles.add("ReadOnly"); existingRoles.add("EmployeLevel"); existingRoles.add("MonitierLevel"); return existingRoles; > >
Printing roles before adding new roles: [ReadOnly, EmployeLevel, MonitierLevel]
Printing roles after adding new roles: [ReadOnly, EmployeLevel, MonitierLevel, TimesheetApprove, LeaveApprove, CabApprove]
Please see the comments given in the above program.
First got all existing roles by calling getExistingRoles method. Then, we have created another new ArrayList object then added new roles to it.
At this point we have two list and values as below.
existingRoles: [ReadOnly, EmployeLevel, MonitierLevel]
newUserRoles: [TimesheetApprove, LeaveApprove, CabApprove]
Next, we want to add newUserRoles to the existingRoles object.
Now observe before and after adding new roles in existingRoles.
Interface List
An ordered collection (also known as a sequence). The user of this interface has precise control over where in the list each element is inserted. The user can access elements by their integer index (position in the list), and search for elements in the list.
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.
Unmodifiable Lists
- They are unmodifiable. Elements cannot be added, removed, or replaced. Calling any mutator method on the List will always cause UnsupportedOperationException to be thrown. However, if the contained elements are themselves mutable, this may cause the List's contents to appear to change.
- They disallow null elements. Attempts to create them with null elements result in NullPointerException .
- They are serializable if all elements are serializable.
- The order of elements in the list is the same as the order of the provided arguments, or of the elements in the provided array.
- The lists and their subList views implement the RandomAccess interface.
- They are value-based. Programmers should treat instances that are equal as interchangeable and should not use them for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail. Callers should make no assumptions about the identity of the returned instances. Factories are free to create new instances or reuse existing ones.
- They are serialized as specified on the Serialized Form page.
This interface is a member of the Java Collections Framework.