Solution for Stream API 01

Exercise.java

@@ -1,6 +1,8 @@
 public class Exercise {
 
   public static void main(String[] args) {
-    // implement exercise here
+    Queries queries = new Queries(DataProvider.getConsoles());
+    System.out.println(queries.getAllConsolesByMaker());
+    // make more queries as you wish
   }
 }

Queries.java

@@ -0,0 +1,73 @@
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.OptionalDouble;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class Queries {
+  private ArrayList<Console> consoles;
+
+  public Queries(ArrayList<Console> consoles) {
+    this.consoles = consoles;
+  }
+
+  public List<String> getAllCurrentConsoleNames() {
+    return consoles.stream()
+        .filter(console -> console.lifespan() == -1)
+        .map(console -> console.title())
+        .toList();
+  }
+
+  public Map<Maker, List<Console>> getAllConsolesByMaker() {
+    return consoles.stream().collect(Collectors.groupingBy(console -> console.maker()));
+  }
+
+  public List<Console> getAllConsolesSortedByLifespan() {
+    Comparator<Console> lifeSpanAscending =
+        (console1, console2) -> Integer.compare(console1.lifespan(), console2.lifespan());
+    return consoles.stream().sorted(lifeSpanAscending).collect(Collectors.toList());
+  }
+
+  public OptionalDouble getAverageSoldUnitsInMillionsPerYearFromAllOutdatedConsoles() {
+    return consoles.stream()
+        .filter(console -> console.lifespan() != -1)
+        .mapToDouble(console -> console.soldUnitsInMillions() / console.lifespan())
+        .average();
+  }
+
+  public long getNumberOfConsolesFromNintendo() {
+    return consoles.stream().filter(console -> console.maker().equals(Maker.NINTENDO)).count();
+  }
+
+  public List<String> getSoldUnitsInMillionsPerYearFromAllOutdatedConsoles() {
+    return consoles.stream()
+        .filter(console -> console.lifespan() != -1)
+        .map(
+            console ->
+                console.title() + " (" + console.soldUnitsInMillions() / console.lifespan() + ")")
+        .toList();
+  }
+
+  public Map<Maker, Double> getTotalSoldUnitsInMillionsPerMaker() {
+    Function<Entry<Maker, List<Console>>, Maker> entrySetToMaker = entrySet -> entrySet.getKey();
+    Function<Entry<Maker, List<Console>>, Double> entrySetToSoldUnits =
+        entrySet ->
+            entrySet.getValue().stream()
+                .mapToDouble(console -> console.soldUnitsInMillions())
+                .sum();
+
+    return getAllConsolesByMaker().entrySet().stream()
+        .collect(Collectors.toMap(entrySetToMaker, entrySetToSoldUnits));
+  }
+
+  public boolean isAllConsolesWithMoreThan50MillionSoldUnits() {
+    return consoles.stream().allMatch(console -> console.soldUnitsInMillions() > 50);
+  }
+
+  public boolean isAnyConsoleWithMoreThan150MillionSoldUnits() {
+    return consoles.stream().anyMatch(console -> console.soldUnitsInMillions() > 150);
+  }
+}