Java 8 - Stream - value update while collecting

Question

In extension the previous question Java 8 - Calling a multi argument method from Collection.stream.map(), how can we update the values while collecting in collect() after stream().map() process?

String designation = "Engineer";
String preFix = "PRE_FIX";
List<String> names = new ArrayList<>();
names.add("ABC");
names.add("DEF");
names.add("GHI");
System.out.println(
    names.stream()
         .map(name -> 
              MyClass.createReport(name, designation))
         .collect(ArrayList::new, ArrayList::add, ArrayList::addAll));

public static String createReport(String name, String designation) {
   return ("Name:" + name + " - Designation:" + designation);
}

Output:

[Name:ABC - Designation:Engineer, Name:DEF - Designation:Engineer, 
 Name:GHI - Designation:Engineer]

Expected:

[PRE_FIX->Name:ABC - Designation:Engineer, PRE_FIX->Name:DEF - 
 Designation:Engineer, PRE_FIX->Name:GHI - Designation:Engineer]

`....map(name -> preFix + "->" + MyClass.createReport(name, designation))..` — Jai, Nov 30 '18 at 06:11
your asking the question in SOF. and u have given the answer... what is this prasad. — Lova Chittumuri, Nov 30 '18 at 07:03

score 4 · Answer 1 · edited Nov 30 '18 at 06:12

4

Use another map()

System.out.println(
      names.stream()
           .map(name -> FolderDiffGenerator.createReport(name, 
                        designation))**
           .map(result -> preFix + "->" +result)**
           .collect(ArrayList::new, ArrayList::add, ArrayList::addAll));

edited Nov 30 '18 at 06:12

ernest_k

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answered Nov 30 '18 at 06:03

Spartan

339
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14

score 1 · Answer 2 · answered Nov 30 '18 at 07:37

Just add the prefix before the invocation to createReport:

names.stream()
     .map(name -> preFix + "->" + MyClass.createReport(name, designation))
     .collect(ArrayList::new, ArrayList::add, ArrayList::addAll);

On another note, .collect(ArrayList::new, ArrayList::add, ArrayList::addAll); can be simplified to .collect(toCollection(ArrayList::new));:

names.stream()
     .map(name -> preFix + "->" + MyClass.createReport(name, designation))
     .collect(toCollection(ArrayList::new));

Java 8 - Stream - value update while collecting

2 Answers2