ArrayList class in Java is basically a resize-able array i.e. it can grow and shrink in size dynamically according to the values that we add or remove to/from it. It is present in java.util package. If we want to pass an ArrayList as an argument to a function then we can easily do it using the syntax mentioned below. Example: ArrayList<Integer> list = new ArrayList<>();
modifyList(list);
public static void modifyList(ArrayList<Integer> list){
list.add(69);
list.add(98);
}In the code above, we created an ArrayList object named ‘list’ and then we passed it to a function named modifyList. The changes that we did to this list (i.e. the values that we added to the list) will appear to the original list inside the main function. This is happening because the Object References are passed by value in java as java is strictly Pass by Value. Implementation of the problem statement:
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public static void main(String[] args)
ArrayList<Integer> list = new ArrayList<>();
System.out.print("ArrayList after insertions: ");
System.out.print("ArrayList after modifications: ");
modifyList(ArrayList<Integer> parameterList)
public static void display(ArrayList<Integer> list)
System.out.println(list);
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Output
ArrayList after insertions: [3, 57, 7]
ArrayList after modifications: [3, 57, 7, 20, 98]
How Java is pass by Value? Let us assume that the Array list object that we created inside the main function points to an address 1000. When we passed this object to the modifyList function then the address 1000 is passed to it and the object ‘parameterList’ also starts pointing to the same location inside the memory as that of ‘list’ that is why we said that object references are passed by value in java. After that when we did modifications to ‘parameterList’ then the same changes are made to the original ‘list’. This concept is very similar to what happens in C++ when we pass a pointer variable as an argument. ArrayList<Integer> list = new ArrayList<>();
callByValue(list);
public static void callByValue(ArrayList<Integer> parameterList){
parameterList = new ArrayList<>();
parameterList.add(88);
parameterList.add(200);
parameterList.add(89);
}In the code above when we passed the list to the callByValue function then the ‘parameterList’ starts pointing to the memory address i.e. 1000. But when we created a new instance of ArrayList and made ‘parameterList’ point to it then ‘parameterList’ starts pointing to a new memory address (let’s say) 2000. The changes made to ArrayList inside this function will no longer affect the ArrayList at memory address 1000. Hence, the ‘list’ inside the main function remains unaffected. Below is the implementation of the problem statement:
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import java.util.ArrayList;
public static void main(String[] args)
ArrayList<Integer> list = new ArrayList<>();
System.out.print("ArrayList after insertions: ");
"ArrayList after the function call: ");
callByValue(ArrayList<Integer> parameterList)
parameterList = new ArrayList<>();
"New ArrayList inside the function: ");
public static void display(ArrayList<Integer> list)
System.out.println(list);
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Output
ArrayList after insertions: [3, 57, 7]
New ArrayList inside the function: [88, 200, 89]
ArrayList after the function call: [3, 57, 7]
Article Tags :
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Type Parameters:
E - the type of elements in this list
All Superinterfaces:
Collection<E>, Iterable<E>
All Known Implementing Classes:
AbstractList, AbstractSequentialList, ArrayList, AttributeList, CopyOnWriteArrayList, LinkedList, RoleList, RoleUnresolvedList, Stack, Vector
public interface List<E>
extends Collection<E>
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. This interface is a member of the Java Collections Framework.
Since:
1.2
See Also:
Collection, Set, ArrayList, LinkedList, Vector, Arrays.asList(Object[]), Collections.nCopies(int, Object), Collections.EMPTY_LIST, AbstractList, AbstractSequentialList
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- parallelStream, removeIf, stream
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-
- Object[] toArray()
Returns an array containing all of the elements in this list in proper sequence (from first to last element). The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array even if this list is backed by an array). The caller is thus free to modify the returned array. This method acts as bridge between array-based and collection-based APIs.
Specified by:
toArray in interface Collection<E>
Returns:
an array containing all of the elements in this list in proper sequence
See Also:
Arrays.asList(Object[])
- <T> T[] toArray(T[] a)
Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list. If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the list is set to null. (This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.) Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs. Suppose x is a list known to contain only strings. The following code can be used to dump the list into a newly allocated array of String:
String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to toArray().
Specified by:
toArray in interface Collection<E>
Type Parameters:
T - the runtime type of the array to contain the collection
Parameters:
a - the array into which the elements of this list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
Returns:
an array containing the elements of this list
Throws:
ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this list
NullPointerException - if the specified array is null
- boolean add(E e)
Appends the specified element to the end of this list (optional operation). Lists that support this operation may place limitations on what elements may be added to this list. In particular, some lists will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. List classes should clearly specify in their documentation any restrictions on what elements may be added.
Specified by:
add in interface Collection<E>
Parameters:
e - element to be appended to this list
Returns:
true (as specified by Collection.add(E))
Throws:
UnsupportedOperationException - if the add operation is not supported by this list
ClassCastException - if the class of the specified element prevents it from being added to this list
NullPointerException - if the specified element is null and this list does not permit null elements
IllegalArgumentException - if some property of this element prevents it from being added to this list
- boolean remove(Object o)
Removes the first occurrence of the specified element from this list, if it is present (optional operation). If this list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).
Specified by:
remove in interface Collection<E>
Parameters:
o - element to be removed from this list, if present
Returns:
true if this list contained the specified element
Throws:
ClassCastException - if the type of the specified element is incompatible with this list (optional)
NullPointerException - if the specified element is null and this list does not permit null elements (optional)
UnsupportedOperationException - if the remove operation is not supported by this list
- boolean addAll(Collection<? extends E> c)
Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (Note that this will occur if the specified collection is this list, and it's nonempty.)
Specified by:
addAll in interface Collection<E>
Parameters:
c - collection containing elements to be added to this list
Returns:
true if this list changed as a result of the call
Throws:
UnsupportedOperationException - if the addAll operation is not supported by this list
ClassCastException - if the class of an element of the specified collection prevents it from being added to this list
NullPointerException - if the specified collection contains one or more null elements and this list does not permit null elements, or if the specified collection is null
IllegalArgumentException - if some property of an element of the specified collection prevents it from being added to this list
See Also:
add(Object)
- boolean addAll(int index, Collection<? extends E> c)
Inserts all of the elements in the specified collection into this list at the specified position (optional operation). Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in this list in the order that they are returned by the specified collection's iterator. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (Note that this will occur if the specified collection is this list, and it's nonempty.)
Parameters:
index - index at which to insert the first element from the specified collection
c - collection containing elements to be added to this list
Returns:
true if this list changed as a result of the call
Throws:
UnsupportedOperationException - if the addAll operation is not supported by this list
ClassCastException - if the class of an element of the specified collection prevents it from being added to this list
NullPointerException - if the specified collection contains one or more null elements and this list does not permit null elements, or if the specified collection is null
IllegalArgumentException - if some property of an element of the specified collection prevents it from being added to this list
IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())
- default void sort(Comparator<? super E> c)
Sorts this list according to the order induced by the specified Comparator. All elements in this list must be mutually comparable using the specified comparator (that is, c.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the list). If the specified comparator is null then all elements in this list must implement the Comparable interface and the elements' natural ordering should be used. This list must be modifiable, but need not be resizable.
Implementation Requirements:
The default implementation obtains an array containing all elements in this list, sorts the array, and iterates over this list resetting each element from the corresponding position in the array. (This avoids the n2 log(n) performance that would result from attempting to sort a linked list in place.)
Implementation Note:
This implementation is a stable, adaptive, iterative mergesort that requires far fewer than n lg(n) comparisons when the input array is partially sorted, while offering the performance of a traditional mergesort when the input array is randomly ordered. If the input array is nearly sorted, the implementation requires approximately n comparisons. Temporary storage requirements vary from a small constant for nearly sorted input arrays to n/2 object references for randomly ordered input arrays. The implementation takes equal advantage of ascending and descending order in its input array, and can take advantage of ascending and descending order in different parts of the same input array. It is well-suited to merging two or more sorted arrays: simply concatenate the arrays and sort the resulting array. The implementation was adapted from Tim Peters's list sort for Python ( TimSort). It uses techniques from Peter McIlroy's "Optimistic Sorting and Information Theoretic Complexity", in Proceedings of the Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, January 1993.
Parameters:
c - the Comparator used to compare list elements. A null value indicates that the elements' natural ordering should be used
Throws:
ClassCastException - if the list contains elements that are not mutually comparable using the specified comparator
UnsupportedOperationException - if the list's list-iterator does not support the set operation
IllegalArgumentException - (optional) if the comparator is found to violate the Comparator contract
Since:
1.8
- boolean equals(Object o)
Compares the specified object with this list for equality. Returns true if and only if the specified object is also a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements e1 and e2 are equal if (e1==null ? e2==null : e1.equals(e2)).) In other words, two lists are defined to be equal if they contain the same elements in the same order. This definition ensures that the equals method works properly across different implementations of the List interface.
Specified by:
equals in interface Collection<E>
Overrides:
equals in class Object
Parameters:
o - the object to be compared for equality with this list
Returns:
true if the specified object is equal to this list
See Also:
Object.hashCode(), HashMap
- int hashCode()
Returns the hash code value for this list. The hash code of a list is defined to be the result of the following calculation:
int hashCode = 1;
for (E e : list)
hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
This ensures that list1.equals(list2) implies that list1.hashCode()==list2.hashCode() for any two lists, list1 and list2, as required by the general contract of Object.hashCode().
Specified by:
hashCode in interface Collection<E>
Overrides:
hashCode in class Object
Returns:
the hash code value for this list
See Also:
Object.equals(Object), equals(Object)
- int indexOf(Object o)
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
Parameters:
o - element to search for
Returns:
the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element
Throws:
ClassCastException - if the type of the specified element is incompatible with this list (optional)
NullPointerException - if the specified element is null and this list does not permit null elements (optional)
- int lastIndexOf(Object o)
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the highest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
Parameters:
o - element to search for
Returns:
the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
Throws:
ClassCastException - if the type of the specified element is incompatible with this list (optional)
NullPointerException - if the specified element is null and this list does not permit null elements (optional)
- ListIterator<E> listIterator(int index)
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call to next. An initial call to previous would return the element with the specified index minus one.
Parameters:
index - index of the first element to be returned from the list iterator (by a call to next)
Returns:
a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list
Throws:
IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())
- List<E> subList(int fromIndex,
int toIndex)
Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive. (If fromIndex and toIndex are equal, the returned list is empty.) The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa. The returned list supports all of the optional list operations supported by this list. This method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a list can be used as a range operation by passing a subList view instead of a whole list. For example, the following idiom removes a range of elements from a list:
list.subList(from, to).clear();
Similar idioms may be constructed for indexOf and lastIndexOf, and all of the algorithms in the Collections class can be applied to a subList. The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)
Parameters:
fromIndex - low endpoint (inclusive) of the subList
toIndex - high endpoint (exclusive) of the subList
Returns:
a view of the specified range within this list
Throws:
IndexOutOfBoundsException - for an illegal endpoint index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex)
- default Spliterator<E> spliterator()
Specified by:
spliterator in interface Collection<E>
Specified by:
spliterator in interface Iterable<E>
Implementation Requirements:
The default implementation creates a late-binding spliterator from the list's Iterator. The spliterator inherits the fail-fast properties of the list's iterator.
Implementation Note:
The created Spliterator additionally reports Spliterator.SUBSIZED.
Returns:
a Spliterator over the elements in this list
Since:
1.8
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