Reads and links May 1st to May 15th 2018

Links Thoughts
Day one course Like Shawn’s material. I did not buy it, as am already a power user of Dayone. If you thinking about journaling, I would think this would be wonderful
Concurrency and Parallelism Simple explanation about the most powerful concepts in programming.
Kids view Another great writeup from NPR for
Startup ideas This was a good overview if ur in a startup. Not sure if I can translate this in a big shop where I’m used to.
GDPR Am sure am not alone in getting all GDPR privacy update emails. This link was a good overview.

JAVA 9 takeWhile and doWhile

Trying to get my hands wet with Java 9. Looks like the streams have got another round of good method updates. Here in this gist, we are trying to demonstrate the takeWhile and the dropWhile filter in the Java 9.
public static List createSong() {
return Arrays
.asList(new Song("Venilave", 2000, "Rehman"), new Song("Va Va Vasanthame", 2002, "Raja"), new Song("Vanjokotiya", 2010, "Raja"), new Song("semmaFigure", 2008, "Rehman"), new Song("Arabic kadloram", 2001, "Rehman"), new Song("Anjali Anjali", 1995, "Raja"), new Song("Pen alla Pen alla", 2010, "Rehman"));
}
public static void main(String args[]) {
createSong().stream().takeWhile(song -> song.getAlbumYear() System.out.println(song.getAlbumYear())).map(Song::getName)
.map(String::toUpperCase).forEach(System.out::println);
}

takeWhile method

Operates on a stream and in the code, we are trying to identify the songs that were from the year that is less than 2002. This condition qualifies only one record to be returned. The returned data is

2000
VENILAVE

dropWhile method

Aging this operates on a stream as well, and this one returns all the records whose album year is after 2002. So we get back the following records.

public class Song {
private String name;
private int albumYear;
private String genre;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAlbumYear() {
return albumYear;
}
public void setAlbumYear(int albumYear) {
this.albumYear = albumYear;
}
public String getGenre() {
return genre;
}
public void setGenre(String genre) {
this.genre = genre;
}
public Song(String name, int albumYear, String genre){
this.name=name;
this.albumYear=albumYear;
this.genre=genre;
}

2002
VA VA VASANTHAME
2010
VANJOKOTIYA
2008
SEMMAFIGURE
2001
ARABIC KADLORAM
1995
ANJALI ANJALI
2010
PEN ALLA PEN ALLA

 

Freecode camp checkCashRegister problem.

I did not like the solution to this problem. But here it is., the question was about giving exact change back to user. The probiem with a $100 spent for a $3.26 purchase.


    var changeGiven = [];
    var total = 0;
    var quarters = 0;
    var pennies = 0;
    var nickels = 0;
    var dimes = 0;
    for (var totalCount = 0; totalCount < cid.length; totalCount++) {
        total = total + cid[totalCount][1];
        if (cid[totalCount][0] === "QUARTER") {
            quarters = Math.round((cid[totalCount][1] * 100 / 25), 2);
        } else if (cid[totalCount][0] === "PENNY") {
            pennies = Math.round((cid[totalCount][1] * 100 / 1), 2);
        } else if (cid[totalCount][0] === "NICKEL") {
            nickels = Math.round((cid[totalCount][1] * 100 / 5), 2);
        } else if (cid[totalCount][0] === "DIME") {
            dimes = Math.round((cid[totalCount][1] * 100 / 10), 2);
        }
    }
        return changeGiven
 

The above block solves most of the items that is needed to solve the problem. But when we are working on the $100 problem, where cashRegister had to return some definite values., here is the code snippet for that.


    var changeToGive = cash - price;
    runningChange = changeToGive;
    var runningChange;
    var twenties;
    if (total - changeToGive == 0) {
        return "Closed";
    } else if (total - changeToGive < 1) {
        return "Insufficient Funds";
    }

    if ((changeToGive  1 && changeToGive > 20) {
        twenties = cid.find(function (element) {
            return element[0] == "TWENTY";
        });
        if (changeToGive > twenties[1]) {
            runningChange = parseFloat(
                Math.round((runningChange - twenties[1]) * 100) / 100).toFixed(
                2);
        }
        changeToGive = runningChange;
        if (runningChange > 0) {
            changeGiven.push([twenties[0], parseFloat(twenties[1].toFixed(2))]);
        }

    }
    var tens;
    if (changeToGive > 1 && changeToGive > 10) {
        tens = cid.find(function (element) {
            return element[0] == "TEN";
        });
        if (changeToGive > tens[1]) {
            runningChange = parseFloat(
                Math.round((runningChange - tens[1]) * 100) / 100).toFixed(2);
        }
        changeToGive = runningChange;
        if (runningChange > 0) {
            changeGiven.push([tens[0], parseFloat(tens[1].toFixed(2))]);
        }

    }
    var fives;
    if (runningChange > 1 && changeToGive > 5) {
        fives = cid.find(function (element) {
            return element[0] == "FIVE";
        });
        if (changeToGive > fives[1]) {
            console.log("Fives more" + fives[1]);
        }
        runningChange = parseFloat(
            Math.round((runningChange - fives[1]) * 100) / 100).toFixed(2);
        if (runningChange > 1) {
            changeGiven.push([fives[0], parseFloat(fives[1].toFixed(2))]);
        } else {
            runningChange = parseFloat(
                runningChange - Math.floor(runningChange / 5) * 5).toFixed(2);
            var temp = ((Math.floor(changeToGive / 5) * 5) / 5);
            changeToGive = runningChange;
            changeGiven.push(["FIVE", parseFloat((temp * 5).toFixed(2))]);
            console.log(changeGiven);
        }
    }
    var ones;
    if (runningChange > 1 && changeToGive > 1) {
        ones = cid.find(function (element) {
            return element[0] == "ONE";
        });
        changeGiven.push(
            ["ONE", parseFloat(Math.floor(runningChange).toFixed(2))]);
        runningChange = runningChange - Math.floor(runningChange);
        changeToGive = runningChange;
        console.log(changeGiven);
    }
    if (runningChange * 100 > 24 || ((runningChange * 100)) % 25 == 0) {
        changeGiven.push(["QUARTER",
            parseFloat(Math.floor(runningChange / 0.25) * .25.toFixed(2))]);
        runningChange = runningChange - Math.floor(runningChange / 0.25) * .25;
        changeToGive = runningChange;
        console.log(changeGiven);
    }
    if (runningChange * 100 > 10) {
        changeGiven.push(["DIME",
            parseFloat((Math.floor(runningChange / 0.10) * .10).toFixed(2))]);
        runningChange = runningChange - Math.floor(runningChange / 0.10) * .10;
        changeGiven.push(["PENNY", parseFloat(runningChange.toFixed(2))]);
        console.log(changeGiven);
    }
    
    

So first we calculated how much money we have to return from a cash register. Then we have three code blocks for the dollar denominations. Each block we check if the amount returned is greater than the money inside cashRegister.
The tricky part was the calculation of the last .76 cents. We first found out how many quarters we have in that denomination. Then went to the nickel and then to dimes.
Finally, the solution needed everything in common float blocks. So before adding to the final array, we made a sanity check to ensure all amounts are on a float.

Design discussion.

This is a great write-up. I liked the fact that, engineers were first trying to be designers. The reason is, they invented the internet and whole technical stack. But designers never fought for their place. This is so true, the design of a designer licensed professional has always turned out better for me. The other point discussed, the ROI of engaging a designer.

SpEL introduction – part 1

SpEL is a powerful utility framework provided by spring for looking up object graph. We will take a look at how to use spEL in this post. We will divide this article into two parts.

We will first create a simple object and see how SpEL is used for reading and manipulating the object graph and then in the second part of the article, we will define a properites file. Read the properties and assign it to a object variable.

SpEL expression evaluation interface

We will take take a simple object here and see how to use the expression api’s to manipulate the object.


public class SampleProgrammer{
        public String name;
        public String occupation
        @Autowired
        SampleProgrammer(String name, String occupation) {
            this.name = name;
            this.occupation = occupation;
        }
}

Now we will create the object and see how to parse the object using SpEL.


       ...
        SampleProgrammer programmer = new SampleProgrammer("Sathish Jayapal", "Programmer");
        ExpressionParser expressionParser = new SpelExpressionParser();
        Expression nameExpression = programmer.parseExpression("name");
        Expression occupExpression = programmer.parseExpression("occupation");
     // EvaluationContext context = new StandardEvaluationContext(programmer);
        String name = (String) nameExpression.getValue(programmer);
        String occupation = (String) occupExpression.getValue(programmer);
        if (logger.isDebugEnabled()) {
            logger.debug("Context Name is " + name);
            logger.debug("Context Occupation is " + occupation);
        }

Looking at the code snippet above, there are few items that we can discuss. We create an Object of the Programmer and manipulate the object tree dynmaically. We are using the expression and its sublass SpelExpressionParser parser. There are two items in the SamplePrgorammer’s programmer object. They are name and occupation. We will define an expression for each class variable. After this we use the expression class to get the value parsed. Here is the code snippet for this :


        ...
        Expression nameExpression = expressionParser.parseExpression("name"); // Define name for expression
        ...
       String name = (String) nameExpression.getValue(programmer);
       ...
       if (logger.isDebugEnabled()) {
            logger.debug("Context Name is " + name);
        ...
        }

We will discuss the reason why this following line of code is commented out.

// EvaluationContext context = new StandardEvaluationContext(programmer);

StandardEvaluationContext uses reflection API’s to identify the constructors and methods. But this is a costly object, in our example we can quickly use the getValue method to get the value.

SpEL by default is interpreter based, all expression are interpreted for evaluation. The reason for this is to give flexibility during evaluation. But if the expression evaluation is not changing often, we can switch the expression to be compiled to JAVA Class. This switch can be done using the [SpringCompilerMode][1] enum parameter. There are few available modes to operate, it is OFF, IMMEDIATE and MIXED. By default SpEL has this in the OFF mode. Immediate mode ensures that expressions are compiled right away. MIXED mode as name suggests expressions are switched between the compile and interepreter mode.

We saw a quick introduction of SpEL and some basic operation in this post. In the next part we will use SpEL to read a properties file and evaluate values.

The sample code for this is in GitHub.