Convert List String to List Integer directly

Question

After parsing my file   s  contains AttributeGet 1 16 10106 10111   So I need to get all the numbers after colon in the attributeIDGet List  I know there are several ways to do it  But is there any way we can Directly convert List lt String gt  to List lt Integer gt   As the below code complains about Type mismatch  so I tried to do the Integer parseInt  but I guess this will not work for List  Here s is String   private static List lt Integer gt  attributeIDGet   new ArrayList lt Integer gt      if s contains  AttributeGet           attributeIDGet   Arrays asList s split      1  split

User · Answer

Why don t you use stream to convert List of Strings to List of integers  like below  List lt String gt  stringList   new ArrayList lt String gt  Arrays asList  10    30    40                50    60    70     List lt Integer gt  integerList   stringList stream                map Integer  valueOf  collect Collectors toList       complete operation could be something like this  String s    AttributeGet 1 16 10106 10111   List lt Integer gt  integerList    s startsWith  AttributeGet           Arrays asList s replace  AttributeGet        split            stream   map Integer  valueOf  collect Collectors toList          new ArrayList lt Integer gt

User · Answer

Using Streams and Lambda   newIntegerlist   listName stream   map x- gt       Integer valueOf x   collect Collectors toList       The above line of code will convert the List of type List lt String gt  to List lt Integer gt    I hope it was helpful

User · Answer

Guava Converters do the trick   import com google common base Splitter  import com google common primitives Longs   final Iterable lt Long gt  longIds        Longs stringConverter   convertAll          Splitter on      trimResults   omitEmptyStrings                splitToList  1 2 3

User · Answer

No  you will have to iterate over each element   for String number   numbers       numberList add Integer parseInt number         The reason this happens is that there is no straightforward way to convert a list of one type into any other type  Some conversions are not possible  or need to be done in a specific way  Essentially the conversion depends on the objects involved and the context of the conversion so there is no  one size fits all  solution  For example  what if you had a Car object and a Person object  You can t convert a List lt Car gt  into a List lt Person gt  directly since it doesn t really make sense

User · Answer

No  there is no way  that I know of   of doing that in Java   Basically you ll have to transform each entry from String to Integer   What you re looking for could be achieved in a more functional language  where you could pass a transformation function and apply it to every element of the list    but such is not possible  it would still apply to every element in the list    Overkill   You can  however use a Function from Google Guava  http   docs guava-libraries googlecode com git javadoc com google common base Function html  to simulate a more functional approach  if that is what you re looking for   If you re worried about iterating over the list twice  then instead of split use a Tokenizer and transform each integer token to Integer before adding to the list

User · Answer

Here is another example to show power of Guava  Although  this is not the way I write code  I wanted to pack it all together to show what kind of functional programming Guava provides for Java   Function lt String  Integer gt  strToInt new Function lt String  Integer gt          public Integer apply String e             return Integer parseInt e            String s    AttributeGet 1 16 10106 10111    List lt Integer gt  attributeIDGet   s contains  AttributeGet        FluentIterable     from Iterables skip Splitter on CharMatcher anyOf        split s    1       transform strToInt      toImmutableList       new ArrayList lt Integer gt

User · Answer

No  you need to loop over the array  for String s   strList  intList add Integer valueOf s

User · Answer

Use Guava transform method as below   List intList    Lists transform stringList  Integer  parseInt

User · Answer

Using lambda   strList stream   map org apache commons lang3 math NumberUtils  toInt  collect Collectors toList

User · Answer

If you re allowed to use lambdas from Java 8  you can use the following code sample   final String text    1 2 3 4 5   final List lt Integer gt  list   Arrays asList text split       stream      map s - gt  Integer parseInt s      collect Collectors toList     System out println list     No use of external libraries  Plain old new Java

User · Answer

If you use Google Guava library this is what you can do  see Lists transform      String s    AttributeGet 1 16 10106 10111         List lt Integer gt  attributeIDGet   new ArrayList lt Integer gt          if s contains  AttributeGet               List lt String gt  attributeIDGetS   Arrays asList s split      1  split                attributeIDGet           Lists transform attributeIDGetS  new Function lt String  Integer gt                  public Integer apply String e                    return Integer parseInt e                                      Yep  agree with above answer that s it s bloated  but stylish  But it s just another way

User · Answer

Using Java8   stringList stream   map Integer  parseInt  collect Collectors toList

User · Answer

You can use the Lambda functions of Java 8 to achieve this without looping      String string    1  2  3  4       List lt Integer gt  list   Arrays asList string split       stream   map s - gt  Integer parseInt s trim     collect Collectors toList

[java] Convert List<String> to List<Integer> directly

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