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 lt W length   i                 System out println W i

User · Answer

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.

User · Answer

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  lt String gt  list   new ArrayList lt  gt     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

User · Answer

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 lt String gt  arr   new ArrayList lt String gt             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

User · Answer

If you use Java 1 5 or beyond you could use   List lt String gt  S   new ArrayList lt String gt     s add  My text     for  String item   S      System out println item

User · Answer

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 lt String gt  list   new ArrayList lt String gt     you should get familiar with Java s extensive API documentation  aka Javadoc   e g  Java 5  Java 6

User · Answer

This should do the trick     String elem    String S get 0     Will return the first item in array   Or  for int i 0   i lt S size     i          System out println S get i

User · Answer

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 lt String gt  names   new ArrayList lt String gt  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

User · Answer

Java 8 introduced default implementation of forEach   inside the Iterable interface   you can easily do it by declarative approach      List lt String gt  values   Arrays asList  Yasir   Shabbir   Choudhary       values forEach  value - gt  System out println value      Here is the code of Iterable interface    default void forEach Consumer lt   super T gt  action        Objects requireNonNull action       for  T t   this            action accept t             Reference

User · Answer

A three line solution  but works quite well   int   source array    0 1 2 3 4 5 6 7 8 9 10 11   ArrayList lt Integer gt  target list   new ArrayList lt Integer gt     for int i   0  i  lt  source array length  i         target list add random array i

User · Answer

You should read collections framework tutorial first of all   But to answer your question this is how you should do it   ArrayList lt String gt  strings   new ArrayList lt String gt     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

[java] How to use an array list in Java?

References

API:

Don't use raw types

Prefer interfaces to implementation classes in type declarations

Naming conventions

Examples related to java

Examples related to arraylist