How can I convert ArrayList Object to ArrayList String

Question

ArrayList lt Object gt  list   new ArrayList lt Object gt     list add 1   list add  Java    list add 3 14   System out println list toString       I tried     ArrayList lt String gt  list2    String list     But it gave me a compile error

User · Answer

With Java Generics Takes a list of X and returns a list of T that extends or implements X  Sweet          the cast is is actually checked via the method API  SuppressWarnings  unchecked   public static  lt T extends X  X gt  ArrayList lt T gt  convertToClazz ArrayList lt X gt  from  Class lt X gt  inClazz  Class lt T gt  outClazz        ArrayList lt T gt  to   new ArrayList lt T gt         for  X data   from            to add  T  data             return to

User · Answer

Since this is actually not a list of strings  the easiest way is to loop over it and convert each item into a new list of strings yourself   List lt String gt  strings   list stream       map object - gt  Objects toString object  null       collect Collectors toList       Or when you re not on Java 8 yet   List lt String gt  strings   new ArrayList lt  gt  list size     for  Object object   list        strings add Objects toString object  null        Or when you re not on Java 7 yet   List lt String gt  strings   new ArrayList lt String gt  list size     for  Object object   list        strings add object    null   object toString     null       Note that you should be declaring against the interface  java util List in this case   not the implementation

User · Answer

Using Java 8 lambda   ArrayList lt Object gt  obj   new ArrayList lt  gt     obj add 1   obj add  Java    obj add 3 14    ArrayList lt String gt  list   new ArrayList lt  gt     obj forEach  xx  - gt  list add String valueOf xx

User · Answer

You can use wildcard to do this as following   ArrayList lt String gt  strList    ArrayList lt String gt   ArrayList lt   gt   list

User · Answer

Using Java 8 you can do   List lt Object gt  list        List lt String gt  strList   list stream                               map  Object  toString                               collect  Collectors toList

User · Answer

It s not safe to do that  Imagine if you had     ArrayList lt Object gt  list   new ArrayList lt Object gt     list add new Employee  Jonh     list add new Car  BMW   M3     list add new Chocolate  Twix       It wouldn t make sense to convert the list of those Objects to any type

User · Answer

A simple solution   List lt Object gt  lst   listOfTypeObject     ArrayList lt String gt  aryLst   new ArrayList lt String gt         for  int i   0  i  lt  lst size    i              aryLst add lst get i  toString             Note  this works when the list contains all the elements of datatype String

User · Answer

Using guava   List lt String gt  stringList Lists transform list new Function lt Object String gt          Override     public String apply Object arg0            if arg0  null              return arg0 toString            else             return  null

User · Answer

Here is another alternative using Guava   List lt Object gt  lst         List lt String gt  ls   Lists transform lst  Functions toStringFunction

User · Answer

Your code ArrayList lt String gt  list2    String list  does not compile because list2 is not of type String  But that is not the only problem

User · Answer

If you want to do it the dirty way  try this    SuppressWarnings  unchecked   public ArrayList lt String gt  convert ArrayList lt Object gt  a       return  ArrayList  a      Advantage  here you save time by not iterating over all objects   Disadvantage  may produce a hole in your foot

[java] How can I convert ArrayList<Object> to ArrayList<String>?

Examples related to java

Examples related to arraylist