How to use an array list in Java?

Question

I need to know if I store my data in an ArrayList and I need to get the value that I've stored in it.

For example : if I have an array list like this

      ArrayList A = new ArrayList();
      A = {"Soad", "mahran"};

and I want to get each String element, how can I do it?

I've tried to do it by the following code:

package arraylist;

import java.util.ArrayList;

public class Main {

        public static void main(String[] args) {
        ArrayList S = new ArrayList();

        String A = "soad ";
        S.add(A);
        S.add("A");
        String F = S.toString();
        System.out.println(F);
        String [] W = F.split(",");
        for(int i=0 ; i<W.length ; i++) {
           System.out.println(W[i]);
        }
    }
}

Answer 1

A three line solution, but works quite well:

int[] source_array = {0,1,2,3,4,5,6,7,8,9,10,11};
ArrayList<Integer> target_list = new ArrayList<Integer>();
for(int i = 0; i < source_array.length; i++){
    target_list.add(random_array[i]);
}

Answer 2

object get(int index) is used to return the object stored at the specified index within the invoking collection.

Code Snippet :

import java.util.*;


class main
{
    public static void main(String [] args)
    {
        ArrayList<String> arr = new ArrayList<String>();
        arr.add("Hello!");
        arr.add("Ishe");
        arr.add("Watson?");

        System.out.printf("%s\n",arr.get(2)); 

        for (String s : arr) 
        {
            System.out.printf("%s\n",s);
        } 
    }
}

Answer 3

First of all you will need to define, which data type you need to keep in your list. As you have mentioned that the data is going to be String, the list should be made of type String.

Then if you want to get all the elements of the list, you have to just iterate over the list using a simple for loop or a for each loop.

List <String> list = new ArrayList<>();
list.add("A");
list.add("B");

for(String s : list){
    System.out.println(s);
}

Also, if you want to use a raw ArrayList instead of a generic one, you will have to downcast the value. When using the raw ArrayList, all the elements are stored in form of Object.

List list = new ArrayList();
list.add("A");
list.add("B");

for(Object obj : list){
    String s = (String) obj; //downcasting Object to String
    System.out.println(s);
}

Answer 4

Java 8 introduced default implementation of forEach() inside the Iterable interface , you can easily do it by declarative approach .

  List<String> values = Arrays.asList("Yasir","Shabbir","Choudhary");

  values.forEach( value -> System.out.println(value));

Here is the code of Iterable interface

  default void forEach(Consumer<? super T> action) {
    Objects.requireNonNull(action);
    for (T t : this) {
        action.accept(t);
    }
}

Reference

Answer 5

A List is an ordered Collection of elements. You can add them with the add method, and retrieve them with the get(int index) method. You can also iterate over a List, remove elements, etc. Here are some basic examples of using a List:

List<String> names = new ArrayList<String>(3); // 3 because we expect the list 
    // to have 3 entries.  If we didn't know how many entries we expected, we
    // could leave this empty or use a LinkedList instead
names.add("Alice");
names.add("Bob");
names.add("Charlie");
System.out.println(names.get(2)); // prints "Charlie"
System.out.println(names); // prints the whole list
for (String name: names) {
    System.out.println(name);  // prints the names in turn.
}

Answer 6

The following snippet gives an example that shows how to get an element from a List at a specified index, and also how to use the advanced for-each loop to iterate through all elements:

    import java.util.*;

    //...

    List<String> list = new ArrayList<String>();
    list.add("Hello!");
    list.add("How are you?");

    System.out.println(list.get(0)); // prints "Hello!"

    for (String s : list) {
        System.out.println(s);
    } // prints "Hello!", "How are you?"

Note the following:

• Generic List<String> and ArrayList<String> types are used instead of raw ArrayList type.
• Variable names starts with lowercase
• list is declared as List<String>, i.e. the interface type instead of implementation type ArrayList<String>.

---

References

API:

• Java Collections Framework tutorial
• class ArrayList<E> implements List<E>
• interface List<E>
  • E get(int index)
    • Returns the element at the specified position in this list.

Don't use raw types

• JLS 4.8 Raw Types

  The use of raw types is allowed only as a concession to compatibility of legacy code. The use of raw types in code written after the introduction of genericity into the Java programming language is strongly discouraged. It is possible that future versions of the Java programming language will disallow the use of raw types.

• Effective Java 2nd Edition: Item 23: Don't use raw types in new code

  If you use raw types, you lose all the safety and expressiveness benefits of generics.

Prefer interfaces to implementation classes in type declarations

• Effective Java 2nd Edition: Item 52: Refer to objects by their interfaces

  [...] you should favor the use of interfaces rather than classes to refer to objects. If appropriate interface types exist, then parameters, return values, variables, and fields should all be declared using interface types.

Naming conventions

Variables: Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter.

Answer 7

You should read collections framework tutorial first of all.

But to answer your question this is how you should do it:

ArrayList<String> strings = new ArrayList<String>();
strings.add("String1");
strings.add("String2");

// To access a specific element:
System.out.println(strings.get(1));
// To loop through and print all of the elements:
for (String element : strings) {
    System.out.println(element);
}

Answer 8

If you use Java 1.5 or beyond you could use:

List<String> S = new ArrayList<String>();
s.add("My text");

for (String item : S) {
  System.out.println(item);
}

Answer 9

You could either get your strings by index (System.out.println(S.get(0));) or iterate through it:

for (String s : S) {
  System.out.println(s);
}

For other ways to iterate through a list (and their implications) see traditional for loop vs Iterator in Java.

Additionally:

• you shouldn't use variable names starting with upper-case letters
• you should parametrize your array list: ArrayList<String> list = new ArrayList<String>();
• you should get familiar with Java's extensive API documentation (aka Javadoc), e.g. Java 5, Java 6

Answer 10

This should do the trick:

String elem = (String)S.get(0);

Will return the first item in array.

Or

for(int i=0 ; i<S.size() ; i++){
     System.out.println(S.get(i));
}