docs: Java Collectors API & Stream Operations – Practice Qs.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Java 8 Crash Course/Java Collectors API/src/Java Collectors API & Stream Operations – Practice Qs.txt

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+Java Collectors API & Stream Operations – Practice Qs:
+
+1. Collecting to a List
+-----------------------
+- What is the purpose of using Collectors.toList() in the following snippet?
+
+  List<String> res = names.stream()
+          .filter(name -> name.startsWith("A"))
+          .collect(Collectors.toList());
+
+- How does filtering and then collecting into a list work in this context?
+
+
+2. Collecting to a Set
+----------------------
+- How does Collectors.toSet() differ from toList() in terms of handling duplicates and ordering?
+
+  Set<Integer> set = nums.stream().collect(Collectors.toSet());
+
+
+3. Collecting to a Specific Collection
+--------------------------------------
+- Explain the use of Collectors.toCollection(() -> new ArrayDeque<>()).
+- In what scenarios might you choose to collect stream elements into an ArrayDeque instead of a List or Set?
+
+
+4. Joining Strings
+------------------
+- How does the Collectors.joining(", ") method operate in this example?
+
+  String concatenatedNames = names.stream()
+          .map(String::toUpperCase)
+          .collect(Collectors.joining(", "));
+
+- What would be the output if the input list is ["Alice", "Bob", "Charlie"]?
+
+
+5. Summarizing Data
+-------------------
+- What information does Collectors.summarizingInt(x -> x) provide?
+
+  IntSummaryStatistics stats = numbers.stream().collect(Collectors.summarizingInt(x -> x));
+
+- What are the main statistical measures available from the IntSummaryStatistics object?
+
+
+6. Calculating Averages
+-----------------------
+- How does Collectors.averagingInt(x -> x) work compared to summarizingInt?
+- Why might you choose one over the other when processing numerical data?
+
+
+7. Counting Elements
+--------------------
+- What is the role of Collectors.counting() in stream processing, and how is it used in this example?
+
+  Long count = numbers.stream().collect(Collectors.counting());
+
+
+8. Grouping Elements
+--------------------
+- Explain how Collectors.groupingBy(String::length) groups elements from the stream.
+- What is the difference between these variations:
+  * groupingBy(String::length)
+  * groupingBy(String::length, Collectors.joining(", "))
+  * groupingBy(String::length, Collectors.counting())
+- How does using a specific map type, as in groupingBy(String::length, TreeMap::new, Collectors.counting()), affect the result?
+
+
+9. Partitioning Elements
+------------------------
+- What is the difference between grouping and partitioning in the context of stream collectors?
+- How does Collectors.partitioningBy(x -> x.length() > 5) split the stream into two groups?
+
+
+10. Mapping and Collecting
+--------------------------
+- Describe how Collectors.mapping(x -> x.toUpperCase(), Collectors.toList()) modifies the stream before collecting.
+- Why might you use a mapping collector instead of applying a mapping function directly on the stream?
+
+
+11. Creating Maps with Collectors.toMap
+---------------------------------------
+- In Example 5, how does Collectors.toMap(x -> x.toUpperCase(), x -> x.length()) construct a map from a stream of strings?
+- What will be the keys and values in the resulting map?
+
+
+12. Handling Duplicate Keys with toMap
+--------------------------------------
+- In Example 6, explain the purpose of the merge function (x, y) -> x + y in:
+
+  words2.stream().collect(Collectors.toMap(k -> k, v -> 1, (x, y) -> x + y))
+
+- What issue does this merge function address when creating a map from elements with duplicate keys?
+
+
+13. Reduction vs. Summing Collector
+-----------------------------------
+- Compare the two approaches used to sum values in a collection:
+
+  items.values().stream().reduce(Integer::sum)
+
+  versus
+
+  items.values().stream().collect(Collectors.summingInt(x -> x))
+
+- What are the differences in terms of the return type and usage?
+
+These questions cover:
+✔ Basic collection
+✔ Advanced grouping/partitioning
+✔ Mapping, averaging, summarizing, and reduction
+
+→ Solid foundation for understanding and discussing the Java Collectors API.