Java 8 Lambda Stream forEach with multiple statements

Question

I am still in the process of learning Lambda  please excuse me If I am doing something wrong  final Long tempId   12345L  List lt Entry gt  updatedEntries   new LinkedList lt  gt      for  Entry entry   entryList        entry setTempId tempId       updatedEntries add entityManager update entry  entry getId           entryList stream   forEach entry - gt  entry setTempId tempId      Seems like forEach can be executed for one statement only  It doesn t return updated stream or function to process further  I might have selected wrong one altogether   Can someone guide me how to do this effectively   One more question   public void doSomething   throws Exception       for Entry entry  entryList           if entry getA      null               printA   throws Exception                    if entry getB      null               printB   throws Exception                    if entry getC      null               printC   throws Exception                          entryList stream   filter entry - gt  entry getA      null  forEach entry - gt  printA     something like this    How do I convert this to Lambda expression

User · Answer

You don t have to cram multiple operations into one stream lambda   Consider separating them into 2 statements   using static import of toList      entryList forEach e- gt e setTempId tempId     List lt Entry gt  updatedEntries   entryList stream      map e- gt entityManager update entry  entry getId        collect toList

User · Answer

Forgot to relate to the first code snippet  I wouldn t use forEach at all  Since you are collecting the elements of the Stream into a List  it would make more sense to end the Stream processing with collect  Then you would need peek in order to set the ID   List lt Entry gt  updatedEntries        entryList stream                 peek e - gt  e setTempId tempId                 collect  Collectors toList       For the second snippet  forEach can execute multiple expressions  just like any lambda expression can    entryList forEach entry - gt      if entry getA      null       printA          if entry getB      null       printB          if entry getC      null       printC              However  looking at your commented attempt   you can t use filter in this scenario  since you will only process some of the entries  for example  the entries for which entry getA      null  if you do

User · Answer

List lt String gt  items   new ArrayList lt  gt     items add  A    items add  B    items add  C    items add  D    items add  E       lambda   Output   A B C D E items forEach item- gt System out println item       Output   C items forEach item- gt       System out println item       System out println item toLowerCase

User · Answer

In the first case alternatively to multiline forEach you can use the peek stream operation   entryList stream             peek entry - gt  entry setTempId tempId             forEach updatedEntries add entityManager update entry  entry getId         In the second case I d suggest to extract the loop body to the separate method and use method reference to call it via forEach  Even without lambdas it would make your code more clear as the loop body is independent algorithm which processes the single entry so it might be useful in other places as well and can be tested separately   Update after question editing  if you have checked exceptions then you have two options  either change them to unchecked ones or don t use lambdas streams at this piece of code at all

[java] Java 8 Lambda Stream forEach with multiple statements

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