map mapToInt mapToDouble collect

Week 7: Enum, Generic Type, Streams, write to file, class diagram/11A. Useful Stream Operations+++

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+The operation 'map' applies the SAME OPERATION to EACH ELEMENT of the stream. 
+Afterwards, the stream is formed from the results of the operations - 'map' can therefore change the type of the stream elements. 
+The operations 'mapToInt' and 'mapToDouble' are special versions of the map operation.
+
+
+For example, if we had a list of 'Teacher' objects and 
+wanted to count the number of teachers whose name is longer than 10 characters, 
+we could use a stream as follows:
+
+// count returns a value of type long
+long count = teachers.stream().map(teacher -> teacher.getName()).
+        filter(name -> name.length() > 10).count();
+
+
+
+
+        
+Another useful stream operation is 'collect'. 
+It allows you to 'FORM A COLLECTION FROM A STREAM' again.
+
+So if we have a list of Teacher objects following the previous example, 
+and we want to create a list of the teachers' email addresses, 
+we can do so by combining the operations 'map' and 'collect':
+
+ArrayList<String> emails = teachers.stream().map(teacher -> teacher.getEmail()).
+                collect(Collectors.toCollection(ArrayList::new));
+ 
+
+
+
+
+Another example where we have a list of integers. 
+We want to create a new list that has only the negative elements from the original list.
+
+Since the 'collect' operation only works on object type streams, 
+we change the stream from 'int' type to 'Integer' type with the boxed() operation 
+before converting to a list:
+
+ArrayList<Integer> negatives = numbers.stream().mapToInt(number -> number).
+                                               filter(number -> number < 0).boxed().
+                                               collect(Collectors.toCollection(ArrayList::new));
+
+
+
+
+
+                
+Let's look at another example where we want to create a new list 
+that only includes those 'Student' objects with less than 30 credits:
+
+ArrayList<Student> lessThan30 = students.stream().
+                                         filter(student -> student.getCredits() < 30).
+                                         collect(Collectors.toCollection(ArrayList::new));
+
+
+
+
+