My Notes

Notes on Programming

• Java
  • jShell
• Groovy
  • XML
  • LDAP
• Typescript
  • Using Yarn
• Scala Notebooks
• Haskell

Here the important commands and information collected while programming.

Java

jShell

To clean the jShell, in the Mac: CMD+K.

To find the type of the variable

public static <T> Class<?> typeOf(final T value) { 
  return value.getClass(); 
}

Groovy

XML

XML processing in the groovy, you need to read xml file to the variable in the groovy shell:

	import groovy.xml.*
	clients = new XmlParser().parseText(new File('sampl.xml').text)
	
	//define namespace
	ns = new Namespace('http://www.my.net.au/uc/bulkexport/clientxml')

Say you need to display the Status of the first Clients/Client

//	<Clients xmlns:'http://www.my.net.au/uc/bulkexport/clientxml'...>
// 		<Client>
//			<Status>Y</Status>
//		</Client>
//		...
//		...
//	</Clients>

println clients.Client[1][ns.Status][0].text()

Your output will be ‘Y’.

//	for all the clients
clients.Client.each { println it[ns.Status].text()}

LDAP

Here the program to test the ldap in groovy. File name is hello.groovy:

import org.apache.directory.groovyldap.LDAP
import org.apache.directory.groovyldap.SearchScope

LDAP con = LDAP.newInstance('ldap://10.25.192.242:389','cn=ojitha,OU=oj Users,DC=aus', 'password')
assert (con.exists('cn=ojitha,OU=oj Users,DC=aus')):" Not exists!"

run as: groovy -cp ~/applications/groovyldap/dist/groovy-ldap.jar hello.groovy The thridparty lib available at https://directory.apache.org/api/groovy-api/1-groovy-ldap-download.html.

Typescript

I use vscode for Typescript development. Install vscode:

brew install --cask visual-studio-code

Any time you can uninstall vscode as follows:

brew uninstall --cask visual-studio-code
rm -rf $HOME/Library/Application Support/Code
rm -rf $HOME/.vscode/

First install nodejs

brew install node

Check node is installed:

node --version

Follow the TypeScript tutorial in Visual Studio Code for more information.

To install typescript

npm install -g typescript

check

tsc --version

To install express:

npm i express

To intsall the express

npm i -D @types/express

My tsconfig.json is:

{
    "compilerOptions": {
        "target": "ES6",
        "module": "CommonJS",
        "outDir": "out",
        "sourceMap": true,
        "esModuleInterop": true,
        "allowSyntheticDefaultImports": true
    }
}

To run the express server:

px ts-node app.ts

The app.ts is:

import express from "express";
const app = express();

app.get('/', (req,res) => {
    res.status(200);
    res.send("Hello")
})

app.listen(3000)

To check type localhost:3000 in the browser.

Using Yarn

Install yarn:

npm install --global yarn

check with

yarn --version

Install typescript:

yarn add typescript --dev

to check

yarn tsc --version

Install express

yarn add express

Scala Notebooks

You can create Scala notebook using docker:

docker run --rm -it \
    -p 127.0.0.1:8192:8192 \
    -p 127.0.0.1:4040-4050:4040-4050 \
    -v `pwd`/config.yml:/opt/config/config.yml \
    -v `pwd`/notebooks:/opt/notebooks/ \
    -v $HOME/.aws:/home/polly/.aws polynote/polynote:latest \
    --config /opt/config/config.yml

You have to have the following config.yml file in your directory

storage:
  dir: /opt/notebooks
  mounts:
    examples:
      dir: examples

Haskell

You can write the basic recursive product of list elements as follows:

myproduct [] = 1
myproduct (n:ns) = n * myproduct ns

This can be replace using foldr as follows:

myproduct n = foldr (*) 1 n

Another example:

To insert value to sorted list:

insertNum x [] = [x] 
insertNum x (y:ys) = if x <= y then x:y:ys else y: insertNum x ys

For inserstion sort

isort [] = []
isort (x:xs) = insertNum x (isort xs)

Above insertion sort can be rewritten as:

isort xs = foldr insertNum [] xs