How to remove all null elements from a ArrayList or String Array

Question

I try with a loop like that     ArrayList tourists  for  Tourist t   tourists        if  t    null                 t setId idForm                 But it isn t nice  Can anyone suggest me a better solution      Some useful benchmarks to make better decision    While loop  For loop and Iterator Performance Test

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for  Iterator lt Tourist gt  itr   tourists iterator    itr hasNext             if  itr next      null    itr remove

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Using Java 8 this can be performed in various ways using streams  parallel streams and removeIf method   List lt String gt  stringList   new ArrayList lt  gt  Arrays asList null   A    B   null   C   null    List lt String gt  listWithoutNulls1   stringList stream                    filter Objects  nonNull                   collect Collectors toList        A B C  List lt String gt  listWithoutNulls2   stringList parallelStream                    filter Objects  nonNull                   collect Collectors toList        A B C  stringList removeIf Objects  isNull      A B C    The parallel stream will make use of available processors and will speed up the process for reasonable sized lists  It is always advisable to benchmark before using streams

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Similar to  Lithium answer but does not throw a  List may not contain type null  error      list removeAll Collections  lt T gt singleton null

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This is easy way to remove default null values from arraylist       tourists removeAll Arrays asList null        otherwise String value  null  remove from arraylist         tourists removeAll Arrays asList  null

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list removeAll Collections singleton null         It will Throws UnsupportedException if you use it on Arrays asList because it give you Immutable copy so it can not be modified  See below the code  It creates Mutable copy and will not throw any exception    public static String   clean final String   v        List lt String gt  list   new ArrayList lt String gt  Arrays asList v        list removeAll Collections singleton null        return list toArray new String list size

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Using Java 8  you can do this using stream   and filter    tourists   tourists stream   filter t - gt  t    null  collect Collectors toList      or  tourists   tourists stream   filter Objects  nonNull  collect Collectors toList      For more info   Java 8 - Streams

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We can use iterator for the same to remove all the null values   Iterator lt Tourist gt  itr  tourists iterator    while itr hasNext         if itr next      null           itr remove

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If you prefer immutable data objects  or if you just dont want to be destructive to the input list  you can use Guava s predicates   ImmutableList copyOf Iterables filter tourists  Predicates notNull

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As of 2015  this is the best way  Java 8    tourists removeIf Objects  isNull     Note  This code will throw java lang UnsupportedOperationException for fixed-size lists  such as created with Arrays asList   including immutable lists

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List lt String gt  colors   new ArrayList lt  gt   Arrays asList  RED   null   BLUE   null   GREEN        using removeIf     Objects isNull   colors removeIf Objects  isNull

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Not efficient  but short  while tourists remove null

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I used the stream interface together with the stream operation collect and a helper-method to generate an new list   tourists stream   filter this  isNotNull  collect Collectors toList      private  lt T gt  boolean isNotNull final T item        return  item    null

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Mainly I m using this    list removeAll Collections singleton null      But after I learned Java 8  I switched to this   List removeIf Objects  isNull

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The Objects class has a nonNull Predicate that can be used with filter   For example   tourists stream   filter Objects  nonNull  collect Collectors toList

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Try   tourists removeAll Collections singleton null      Read the Java API  The code will throw java lang UnsupportedOperationException for immutable lists  such as created with Arrays asList   see this answer for more details

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There is an easy way of removing all the null values from collection You have to pass a collection containing null as a parameter to removeAll   method  List s1 new ArrayList    s1 add null    yourCollection removeAll s1

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I played around with this and found out that trimToSize   seems to work  I am working on the Android platform so it might be different

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Pre-Java 8 you should use   tourists removeAll Collections singleton null      Post-Java 8 use   tourists removeIf Objects  isNull       The reason here is time complexity  The problem with arrays is that a remove operation can take O n  time to complete  Really in Java this is an array copy of the remaining elements being moved to replace the empty spot  Many other solutions offered here will trigger this issue  The former is technically O n m  where m is 1 because it s a singleton null  so O n   You should removeAll of the singleton  internally it does a batchRemove   which has a read position and a write position  And iterates the list  When it hits a null  it simply iterates the read position by 1  When they are the same it passes  when they are different it keeps moving along copying the values  Then at the end it trims to size   It effectively does this internally   public static  lt E gt  void removeNulls ArrayList lt E gt  list        int size   list size        int read   0      int write   0      for    read  lt  size  read              E element   list get read           if  element    null  continue          if  read    write  list set write  element           write              if  write    size            list subList write  size  clear              Which you can explicitly see is an O n  operation   The only thing that could ever be faster is if you iterated the list from both ends  and when you found a null  you set its value equal to the value you found at the end  and decremented that value  And iterated until the two values matched  You d mess up the order  but would vastly reduce the number of values  you set vs  ones you left alone  Which is a good method to know but won t help much here as  set   is basically free  but that form of delete is a useful tool for your belt     for  Iterator lt Tourist gt  itr   tourists iterator    itr hasNext             if  itr next      null    itr remove           While this seems reasonable enough  the  remove   on the iterator internally calls   ArrayList this remove lastRet     Which is again the O n  operation within the remove  It does an System arraycopy   which is again not what you want  if you care about speed  This makes it n 2   There s also   while tourists remove null      Which is O m n 2   Here we not only iterate the list  We reiterate the entire list  each time we match the null  Then we do n 2  average  operations to do the System arraycopy   to perform the remove  You could quite literally  sort the entire collection between items with values and items with null values and trim the ending in less time  In fact  that s true for all the broken ones  At least in theory  the actual system arraycopy isn t actually an N operation in practice  In theory  theory and practice are the same thing  in practice they aren t

[java] How to remove all null elements from a ArrayList or String Array?

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