Java push to arraylist

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.

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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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The push() Function in Java

The push() Function in Java

  1. Use the stack.push() Function in Java
  2. Use the LinkedList.push() Function in Java
  3. Use the ArrayList.add() Function in Java
  4. Use a User-Defined push() Function for Arrays in Java

If we talk about the basic definition of push() function, it will be a function that inserts an element to the end of some structure. This function is associated with Last In First Out structures like stacks, linked lists, and more. Java doesn’t have a push() function for arrays in it.

Since the push() function is not associated with arrays, we can use different data structures that already support this function.

This article will discuss the push() function in Java.

Use the stack.push() Function in Java

We can use the push() function from the stack class. For this, we will be importing the java.util package for using the stack class.

With this function, we can add elements to the end of the stack. The stack can be of some desired type.

We will be creating the stack method of the string type. We will add the elements one by one using the push() function.

import java.util.*; public class Push_Example   public static void main(String args[])   StackString> st = new StackString>();  st.push("Ram");  st.push("shayam");  st.push("sharma");  System.out.println("Stack Elements: " + st);  st.push("monu");  st.push("sonu");  // Stack after adding new elements  System.out.println("Stack after using the push function: " + st); > > 
Stack Elements: [Ram, shayam, sharma] Stack after using the push function: [Ram, shayam, sharma, monu, sonu] 

Use the LinkedList.push() Function in Java

In Java, the push() function is associated with Linked Lists also. For this also, we will be importing the java.util package.

We can define a new linked list using the LinkedList method. Now, we can add elements one by one using the push() function.

import java.util.*; public class Push_Example   public static void main(String args[])   LinkedListInteger> li = new LinkedList<>();  li.push(10);  li.push(11);  li.push(12);  li.push(13);  li.push(14);  System.out.println("LinkedList Elements: " + li); // Push new elements  li.push(100);  li.push(101);  System.out.println("LinkedList after using the push function: " + li); > > 
LinkedList Elements: [14, 13, 12, 11, 10] LinkedList after using the push function: [101, 100, 14, 13, 12, 11, 10] 

Use the ArrayList.add() Function in Java

For ArrayLists, we can use the add() function to emulate the push() function. This function will add an element to the end of the given ArrayList.

import java.util.*; public class Push_Example  public static void main(String args[])  ArrayListInteger> li = new ArrayList<>();  li.add(10);  li.add(11);  li.add(12);  li.add(13);  li.add(14);  System.out.println("ArrayList Elements: " + li); // Push new elements  li.add(100);  li.add(101);  System.out.println("ArrayList after using the add function: " + li); > > 
ArrayList Elements: [10, 11, 12, 13, 14] ArrayList after using the add function: [10, 11, 12, 13, 14, 100, 101] 

Use a User-Defined push() Function for Arrays in Java

There is no push() function for arrays in Java. However, we can create a function to emulate this. This function will copy the array contents to a new array of longer length and add the new element to this array.

import java.util.*; public class Push_Arr   private static String[] push(String[] array, String push)   String[] longer = new String[array.length + 1];  for (int i = 0; i  array.length; i++)  longer[i] = array[i];  longer[array.length] = push;  return longer; > public static void main(String args[])   String[] arr = new String[]"a", "b", "c">;  arr = Push_Arr.push(arr,"d");  System.out.println("Array after using the push function: ");  for(int i=0;iarr.length;i++)  System.out.println(arr[i]); > > 
ArrayList after using the add function: a b c d 

This method gives the desired output but is rarely used because it runs a loop to copy the array elements, so it will take a lot of time and memory when dealing with larger arrays.

Related Article — Java Array

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Java push to arraylist

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.

Field Summary

Fields declared in class java.util.AbstractList

Constructor Summary

Constructs a list containing the elements of the specified collection, in the order they are returned by the collection’s iterator.

Method Summary

Inserts all of the elements in the specified collection into this list, starting at the specified position.

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.

Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.

Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.

Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.

Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.

Removes from this list all of the elements whose index is between fromIndex , inclusive, and toIndex , exclusive.

Returns a view of the portion of this list between the specified fromIndex , inclusive, and toIndex , exclusive.

Returns an array containing all of the elements in this list in proper sequence (from first to last element).

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.

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