Lesson 1 - Lambda expression syntax

Similar Questions

• It is beneficial to create new static methods to replace lambda expressions?

  Simon told us to replace the lambda expression by method handles. Is there an advantage to do so, such as better performance? And it means that it is always advantageous to create new static methods instead of write lambda expressions?

  What Simon says - or should have said - is to use a reference method, is not a handle method. (A method handle is a construction of low level used by the invokedynamic bytecode and as such is much closer to the JVM. "It is not a feature of the Java language).

  In all cases, it can often be a good idea to use a method instead of an explicit lambda expression reference. Performance is not a problem. I did a comparative analysis and I was unable to discern the difference.

  First of all, you may already have a method that does what you want, so if you need a lambda that does the same thing, just write a method reference in the existing method.

  But sometimes it makes sense to take a lambda expression and then replace the lambda with a method reference refactor in a named method. There are several reasons for this:

  • Testability. A named method is easier to unit test to a lambda expression incorporated in a more complex construction as a data flow pipeline.
  • Reuse. The same logic can be used in several places, by calls direct or other references of the method.
  • Readability. If a lambda begins to be too big (in particular, several lines), it can disrupt the readability of a data flow pipeline.
  • Debugging. While most debuggers can today point stop and step by step through lambda expressions, control flow can be confusing.

  It is above all a question of degree. I find that about 95% of the lambda expressions that I write, or calculate something trivial, for example

  x -> x + 1
  

  or call a method in a way that cannot be expressed using a method reference, for example

  (a, b) -> a.foo(b.getBar())
  

  Rarely, I'll write an inline lambda, such as multi-instructions

  x -> { foo(x); bar(x); }
  

  Anything more complicated I'll tend to refactor in a separate method and use a method reference.

  Finally, a method reference can often be an instance instead of a static method method. If you're in an instance method and you want to write a reference to a method that is called on the same instance, you can write

  this::someMethod
  

  refer to it.

• How to use String Manipulation Cloud Connector to shoot the first five characters of the field? (Expression syntax experience)

  The question

  I need to segment data on a large number of Postal Codes, usually about 400 to 600 at the same time. It is that our postcode field includes the last four digits in some cases, for example 92101-1957. When you use the Contact filter 'Value In A' I'm not able to do this 92101 *, 92102 * and of course I can't account for any combination of four numbers that might appear.

  The Solution - in theory

  The solution I came up with that is to create a new field of Contact in Eloqua 'Segmentation Zip Code' copy of the 5 digits of the postal Code field and execute segmentation using this new field.

  The Solution - Cloud Connector

  String Manipulation cloud connector must be able to perform this action - copy on the first 5 digits of the zip in the zip segment field field.

  When I'm stuck - via cloud connector

  I can't figure out how to write the syntax for expressions to search and replace. I have read the instructions of syntax and am still unable to establish exactly what I enter in the "regex to find: ' and the ' Regular Expressions to replace:

  Does anyone have expierence with an Expression syntax that might help train these expressions?

  Any ideas on other ways to address the problem would be too great.

  Thank you

  Louis

  Hi Louis,.

  Okay, I think I might know how to do it now but don't have access to Eloqua for the moment, so I'm kind of make this Store, but try below.

  Use the regex below in the "Regex for find" and let the "Regex to replace white": "."

  -(.*)$

  This will be after the hyphen and the replacement string will be empty, so I hope you should be left with just the first five digits that you can map to a new field.

  Let me know how you get on, I might be able to test myself so tomorrow so I'll see if I can make it work.

  Chris

• Simple bound properties with lambda expressions

  As I am climbing the learning curve, I find myself to write code such as

        more.disableProperty().bind(model.temperatureProperty()
           .greaterThanOrEqualTo(100));
        gauge.widthProperty().bind(model.temperatureProperty()
           .multiply(4));
  

  I can see why he must accumulate these trees of expression with methods such as greaterThanOrEqualTo and multiply , but it seems a bit tedious. So, I thought: why not let the lambdas at work? Feed properties and a lambda that says how they should be evaluated when they change. Like this:

        more.disableProperty().bind(observe(model.temperatureProperty(),
              t -> t >= 100));
        gauge.widthProperty().bind(observe(model.temperatureProperty(),
              t -> 4 * t));
  

  It's maybe just me, but I find it easier on the eyes. The implementation of observe is trivial:

     static class Binding1<T, R> extends ObservableValueBase {
        private ObservableValue<T> obs;
        private Function<T, R> fun;
        
        public Binding1(ObservableValue<T> obs, Function<T, R> fun) {
           this.obs = obs;
           this.fun = fun;
           obs.addListener(o -> fireValueChangedEvent());         
        }
  
        public R getValue() {
           return fun.apply(obs.getValue());
        }
     }
  
     public static <T, R> ObservableValue<R> observe(ObservableValue<T> obs, Function<T, R> fun) {
        return new Binding1<T, R>(obs, fun);
     }
  

  We could use a couple more of these functions to handle the lambdas with 2 and maybe 3 to 4 parameters.

  With this approach, there is no real need to use such things as DoubleProperty because you can do assessments in the lambda and don't need a bunch of methods to replicate the arithmetic operations.

  Someone has already thought along those lines, or am I innovate here? Or I forgot something that would condemn this approach?

  The class of links has a bunch of useful methods to create links, including createObjectBinding (...), which I think is more or less what you are looking for here:

  import javafx.beans.binding.Bindings;
  import javafx.beans.property.BooleanProperty;
  import javafx.beans.property.DoubleProperty;
  import javafx.beans.property.SimpleBooleanProperty;
  import javafx.beans.property.SimpleDoubleProperty;
  
  public class BindingsWithLambdaTest {
  
    public static void main(String[] args) {
      final DoubleProperty temp = new SimpleDoubleProperty();
      final BooleanProperty more = new SimpleBooleanProperty();
      final DoubleProperty gauge = new SimpleDoubleProperty();
  
      more.bind(Bindings.createObjectBinding(
          () -> temp.doubleValue() >= 100,
          temp)
      );
      gauge.bind(Bindings.createObjectBinding(
          () -> 4*temp.doubleValue(),
          temp)
      ); 
  
      more.addListener(
          (observable, oldValue, newValue) -> System.out.printf("more changed from %s to %s%n", oldValue, newValue)
      );
      gauge.addListener(
          (observable, oldValue, newValue) -> System.out.printf("gauge changed from %.1f to %.1f%n", oldValue.doubleValue(), newValue.doubleValue())
      );
  
      temp.set(10);
      temp.set(40);
      temp.set(110);
    }
  
  }
  

  Post edited by: James_D (additional code example)

• in the query expression syntax error

  I get the following error message:
  
  Microsoft] [ODBC Microsoft Access driver] syntax error (missing operator) in query expression 'customerid_cus ='.
  
  for the following code:
  
  If IsEmpty (Request.Form("company_cus")) then
  
  rs_company. Source = "SELECT customerid_cus, company_cus FROM customers_cus WHERE customerid_cus =" & Request.QueryString ("customerid") & "". "
  
  On the other
  
  rs_company. "Source =" SELECT customerid_cus, company_cus FROM customers_cus WHERE company_cus = ' "& Request.Form ("company_cus") &" "'"
  
  End If
  
  What could be the problem?

  Are you sure that you pass the customerid querystring when the form
  company_cus is empty.

  --
  Paul Whitham
  Certified Professional Dreamweaver MX2004
  Adobe Community Expert - Dreamweaver

  Valleybiz Web design
  www.valleybiz.NET

  "aonefun" wrote in message
  News:epmf3n$f3u$1@forums. Macromedia.com...
  > I get the following error message:
  >
  [> Microsoft] [ODBC Microsoft Access driver] Syntax error (missing operator)
  > in
  > query expression 'customerid_cus ='.
  >
  > to the following code:
  >
  > If IsEmpty (Request.Form ("company_cus")) then
  >
  > rs_company. Source = "SELECT customerid_cus, company_cus FROM".
  > customers_cus
  "> WHERE customerid_cus =" & Request.QueryString ("customerid") & ""
  >
  > Other
  >
  > rs_company. Source = "SELECT customerid_cus, company_cus FROM".
  > customers_cus
  > WHERE company_cus = ' "& Request.Form ("company_cus") &" ' "
  >
  > End If
  >
  > What could be the problem?
  >

• Expression syntax of

  Hello

  In a 'ADF task Flow', I am using a router to choose what page will display based on the result of a query (if empty, the page has, if not page B).

  There are many options in the router expression builder... but not much related to the results of my query?

  Thanks for your help

  Ben

  Note: I use jdev 12 c

  Not exactly your use case, but it should help you get started. The key is to run the query of vo first, and then check if the iterator returns zero rows or greater than zero.

  Check http://tompeez.wordpress.com/2012/12/01/jdeveloper-11-1-1-5-0-use-router-to-create-new-row-or-edit-existing/for more information.

  Timo

• Lesson 1-1 code is correct?

  Hi all.

  I just started watching a course and have finished all the chapters of lesson 1, no homework and quiz.

  So we in Lesson 1-1 example usage of lambda expressions (with my method createStudentsList() to fill the list):

  Students list < student > = createStudentsList();

  Double highestScore = 0.0;

  for (s student: students) {}

  If (s.getGradYear () == 2011) {}

  If (s.getScore () > highestScore) {}

  highestScore = s.getScore ();

  }

  }

  }

  It compiles and works.

  But the proposed changes by using lambda expressions does not work:

  Students list < student > = createStudentsList();

  Double highestScore = student

  filter (new predicate < student > () {})

  public boolean test (Student's t) {}

  return t.getGradYear () is 2011;

  }

  })

  .map (Mapper new student, < Double > () {})

  public Double extracted (student s) {}

  Return s.getScore ();

  }

  })

  . Max();

  saying "the filter method (new predicate < student > () {}) is undefined for the type List < student >" and "Mapper cannot be resolved to a type.

  Even the latest version of the code does not compile:

  Students list < student > = createStudentsList();

  highestScore = student

  filter (student s-> s.getGradYear () == 2011)

  .map (student s-> s.getScore ())

  . Max();

  with "syntax error, insert ';' to complete the statement" for the two statements of student.

  I managed to make it work with this approach:

  Students list < student > = createStudentsList();

  Double highestScoreL = student

  . Stream()

  filter (s-> s.getGradYear () == 2011)

  .mapToDouble (s-> s.getScore ())

  . Max()

  . getAsDouble();

  I do wrong or just missed sth sth important? Sorry for the question so long - it is because as pieces of code .

  BTW I use Eclipse March 4.5.0 and jdk1.8.0_51 if that matters.

  There is problem with your code. I fixed your code and it would be:

  Student s0 = new Student(2014, 685);

  Student s1 = new Student(2014, 675);

  Student s2 = new Student(2014, 635);

  Student s3 = new Student(2014, 985);

  List of students of = Arrays.asList (s0, s1, s2, s3);

  Stream studentStream;

  studentStream = students.stream ().

  filter (new predicate() {}

  @Override

  public boolean test (Student's t) {}

  return t.getGradYear () is 2014;

  }

  });

  Stream highestScoreStream = studentStream.map (new function() {}

  @Override

  public Double apply (student s) {}

  Return s.getScore ();

  }

  });

  HighScore = highestScoreStream.max of in option (new comparator() {}

  @Override

  public int compare (Double d1, d2 Double) {}

  Return d1.compareTo (d2);

  }

  });

  Double highestScore = highScore.get ();

  System.out.println (highestScore);

  Make sure and tell me if you don't get anything. This is the detailed code pre JDK8 average. Now you can write it as functional programming.

  and Yes... The video code is just for us to understand. It is not syntactically correct as map is not a FunctionalInterface in JDK8.

• Question about lesson 1-7, slide 2: Iterable.forEach () and parallel execution

  As stated in the previous parts of this lesson, the library can choose to run lambda expressions in parallel.

  In the example: the final execution using Iterable.forEach () result will be same as using a traditional loop?

  Using a traditional loop that you are sure that the items in the list are printed in the order they are in the list.

  This is not always true using Iterable.forEach (), since the items could be printed by different threads?

  "... the library can choose to perform lambda expressions in parallel."

  I wanted to clarify a little.

  The general rule is that parallel execution can occur if the particular library used API allows him, and it is usually under the control of the programmer. For example, lambdas in parallel flow (which will be addressed later in the MOOC) can be run in parallel, but the programmer must explicitly request parallelism. If the API says nothing about parallel (or asynchronous) execution, then those that don't occur.

  If Iterable.forEach runs sequentially, and the underlying class specified an order, the execution will take place in this order.

• Lambdas under the hook?

  Hi guys,.

  
  

  I would like to know if the course will offer some knowledge on how lambda expressions is compiled, because during the video Simon said "expressions lambda expression representing a method, but it does not associate with a class" however so far I know lambdas are copied inside the class as "private static methods" and then at run time, there is an anonymous class (created with the dangerous class) that implements the functional interface and calls the method.

  
  

  Maybe my understanding is wrong then I would like to know how the JAVA virtual machine handles lambda expressions, if this topic is not covered by the course, I would like to know if you can supply a material or a good source to read about this subject (also, I read on bootstrap methods but I wasn't able to get the whole picture).

  Thanks in advance.

  Kind regards

  Luis

  It was useful to me, the Translation of Lambda Expressions

• How can I get the expressions runs on compositions?

  I have two comps, each with a layer, and I want the x position of model 1 to order reverse position x on computer 2. Ive been studying expressions for a week but it's slightly above any tutorial I found.

  Just another address the composition of his name. For example:

  COMP("COMP 2"). Layer ("yellow solid 1") .transform .position

  You even don't need to know everything about expression syntax to do it. Just use the pickwhip. (Tip: anchor panel mounting under another one to use the pickwhip through compositions.)

  

• Using ForEach in the duties of Levenshtein

  Hello

  I noticed that in last homework it has been used for each of the approaches in the lambda expression.

  static int[][] computeLevenshtein(List<String> wordList, boolean parallel) {  
  final int LIST_SIZE = wordList.size();  
  int[][] distances = new int[LIST_SIZE][LIST_SIZE];  
      IntStream stream = IntStream.range(0, LIST_SIZE);  
  
  if (parallel)  
        stream = stream.parallel();  // Convert the stream to a parallel one  
  
      stream.forEach(i -> {
  for (int j = 0; j < LIST_SIZE; j++)  
          distances[i][j] = Levenshtein.lev(wordList.get(i), wordList.get(j));
      });
  

  We change the matrix of the distances here. However, in Lesson 3-3 on slides 3 and 4 we are told do not change state using the ForEach method. Or is it only because this slide 3 LongAdder is not thread-safe and so it cannot be run in parallel? Thank you.

  Marian

  My way of thinking:

  The forEach loop is terminal operation and stateless.

  That is, the distance value [i] [j] does not change if you use parallel or sequential flows.

  The trouble begins if you use something like this:

  List distances = new ArrayList<>();
  

  and then later in the code:

  distances.add(Levenshtein.lev(wordList.get(i), wordList.get(j)));
  

  The order in which the items added to the list would be different from execution to execution of the parallel flow.

  Hope that this help

• Non-empty methods as a consumer

  Hello

  I would like to ask a question about the use of methods not void as a consumer in lambda expressions. In blades of lesson 1-4, page 3, it is said that the < T > consumers are "that takes a single value and returns no. result of the operation. So I thought that Java would only accept the void methods, but he accepts something as list.forEach (s-> builder.append (s)); as well. However the method-builder.append () returns StringBuilder. So I guess you meant in the slides that return value is ignored, right? Thank you.

  BTW wonderful courses!

  Marian

  Right, in this case, the return value is ignored.

  The idea is that there are some expressions that can be used as statements; See the Java Language Specification, section 14.8 for gory details. Thus, builder.append ("x") is an expression that returns a StringBuilder. This expression can also be used as a statement she with a semicolon:

  builder.append("x");
  

  (Probably it only would do this for its side effects.) In this case, the return value is ignored.

  It is similar in case a lambda is in a context where the target type is a void method:

  void foo(Consumer csb) { ... }
  
  foo(sb -> sb.append("x"));
  

  If the lambda body is an expression that can also be used as a statement, while the expression can be used as a lambda body where the target type abstract method returns void. (Which is covered by JLS 15.27.3.)

  Note that only a small subset of the expressions can be used as instructions or return void lambdas: invocations of method, assignments, create instance (e.g., new Foo()) and pre/post increment/decrement (a ++, etc.) expressions. Most of the other expressions (for example, 'a + b') cannot.

• Question about the process() in Lession 1-2 method

  Lesson 1-2 contains the statement "String r = process (list, (x, y)-> x.length () - y.length ())", that I do not understand and cannot parse, even if I am a little familiar with lambda expressions. "  The method takes a list of String and a comparator, but the result is assigned to a unique string.  What result returned by this method?

  Looks like you are looking to slide 4 lesson 1-2.

  The example here does not say what the process() method, but one can imagine that she's going through all the items in the list and chooses the one that is the largest according to the provided comparer. This is similar to the Collections.max (Collection, comparator) method. Who is?

  Furthermore, there is a small error in the declaration of the process() method which could give a little trouble. The statement must have a parameter of type:

  static T process(List l, Comparator c)

  If you have problems, the analysis of the code, the line in the example is

  String r = process(list, (x, y) -> x.length() - y.length())

  In this case, the reference parameter is the lambda expression

  (x, y) -> x.length() - y.length()

  This has two parameters which, in this context, must be of type String. The Agency calculates the difference between the lengths, which is an int. Thus, the lambda takes two strings and returns an int. This corresponds to the comparator interface compare() method.

• How to distinguish the events within an EventHandler?

  Hi all,

  being a newbe in JavaFX I try to distinguish the different eventtypes.

  I try to produce a MouseEventHandler accepting soe as MOUSE_DRAGGED and MOUSE_PRESSED events

  for the calculation of how mouse took and use it to translate my graphics nodes.

  I still don't really understand what is the correct syntax.

  something like

  If (event.getEventType instanceof MouseEvent.MOUSE_PRESSED ())

  {

  ...

  }

  obviously does not work.

  something like

  switch (event... getEventType())

  {

  case MOUSE_PRESSED:

  ...

  }

  also isn't the right way.

  Is it possible to tell them apart?

  Thank you very much in advance

  Malta

  if (event.getEventType() == MouseEvent.MOUSE_PRESSED) {
  // ...
  }
  

  should work.

  I've never done this, fwiw. I always just save different implementations of listener for different event types:

  node.addEventHandler(MouseEvent.MOUSE_PRESSED, new EventHandler() {
       @Override
       public void handle(MouseEvent event) {
            // handle mouse pressed
       }
  });
  
  node.addEventHandler(MouseEvent.MOUSE_RELEASED, new EventHandler() {
       @Override
       public void handle(MouseEvent event) {
            // handle mouse released
       }
  });
  

  In Java 8 this will get much less verbose (using lambda expressions).

• Result of log Message Popup Hit button?

  Hi all

  Trying to figure out how to enable a pop-up message in a test (that is the button that is hit determines if the test of success or failure).  I am able to retrieve the result and controls the flow of data based on the result, but cannot find a way to include the result in the report.  I have been working on a 'custom result' in the section 'Other results' tab proerties, but can't seem to get the right expression syntax.  Please notify.  Thank you.

  GSinMN

  Hello

  You can use the expression of State to determine a pass/fail result. For an example, see attached sequence.

  I hope it works for you.

  Mathijs