Exercise 07: Lambda Functions

Kakapo and Aye-Aye

Sources: https://commons.wikimedia.org/wiki/File:Aye-aye_(Daubentonia_madagascariensis).jpg https://en.m.wikipedia.org/wiki/File:Kakapo_Sirocco_1.jpg

This week’s lab work is intended help you better understand lambda functions, and Kara has a comeback to practice iterating through Lists.

Source code for this exercise: https://github.com/htw-imi-info1/exercise07-lambda-expressions

Pre-lab

Please prepare these Exercises *before* coming to lab! Doing the pre-lab will save you time during the lab.

P0. If you have a collection called myList, what Java code would you have to write to apply some code to each of the members in the list?

P1. Given the following code:

public void printStudent (Student s)
{
   System.out.println (s.getDetails());
}

What is the equivalent lambda in Java? What syntax variations are possible?

P2. Given the animal-monitoring-v1 example, write pseudo-code for determining how many elephants a particular spotter saw on a particular day.

P3. Given the animal-monitoring-v1 example, write pseudo-code to create a stream containing only those sightings that have a count greater than 0.

What To Hand In

Please hand in:

zip-folder with your AnimalMonitor code.
Your lab report as a pdf. For more Information on the report see the Labs and Exercises page.

Lab assignments are due on the day before the next labs at 10pm.

Assignment

Part 1: Lambdas

Download the animal-monitoring-v1 https://github.com/htw-imi-info1/exercise07-lambda-expressions project and check that it runs. Now rewrite the printList method in the AnimalMonitor class to use a lambda, just as we did in the lecture. Now apply each of the variations that you recorded in P1, compile them and run them. Did they all work? Record the results for your lab report.
Rewrite the printSightingsOf method in the AnimalMonitor class to use streams and lambdas. Test to make sure that your project still works as before.
Write a method printSightingsInPeriod in the AnimalMonitor class to print the details of all the sightings recorded within a certain period periodID, which is passed as a parameter to the method.
Write a method printSightingsOfInPeriod that uses two filter calls to print details of all the sightings of a particular animal made in a particular period — the method takes the animal name and the periodID as parameters. Does the order of the two filter calls matter in your solution? Justify your answer.
Write a method printCounts to print the counts of all sightings of a particular animal. Your method should use the map operations as part of the pipeline. If a pipeline contains a filter operation and a map operation, does the order of the operations matter to the final result? Justify your answer.
Rewrite the printEndangered method in your project to use streams and test that it works correctly. Detail how you tested this method in your report.
(For the bored) There is a special “::” notation in Java that can be used with lambdas. Research the syntax, and rewrite printSightingsBy to use this syntax. Does the operation of the method change?
(For the bored) Add a method to AnimalMonitor that takes two parameters, a spotter-ID and a day-ID and returns a String containing the names of the animals seen by the spotter on that particular day. You should include only animals whose sighting count is greater than zero. Now add a method that takes an animal and a day-ID and returns the spotters who saw this animal, if any, on that particular day.

Part 2: Kara Mirror

Open the kara-mirror project. Kara should mirror all the leaves on the left hand of the world, like this:

Kara Screenshot

This could be solved by copying each single leaf, but a List<Boolean> makes it much easier - or at least more elegant. The List<Boolean> should store for each field in the row if it contains a leaf in a boolean variable. Use this as a starting point:

    public void act() 
    {
        move();
        mirrorRow();
        if (treeFront())
            Greenfoot.stop();
    }  

    public void mirrorRow(){
        turnLeft();
        List<Boolean> row = scanRow();
        layRow(row);
        turnRight();
    }