albertoielpo/java-roadmap

from zero to dev

Java roadmap

From zero to dev

Intro

What is Java? When use it? Why use it? Stack, Heap, Static and garbage collector

Resources

• Getting started: https://spring.io/projects/spring-boot
• Blog: https://www.baeldung.com
• Spring Doc: https://docs.spring.io/spring-framework/reference/overview.html
• MVC vs Reactive: https://spring.io/reactive
• Maven repository: https://mvnrepository.com/
• Gradle guide: https://gradle.org/guides/

Setup environment

IDE: Eclipse, IntelliJ and VsCode

Setup new origin

git remote add origin https://github.com/albertoielpo/java-roadmap.git

Extensions VSCODE

• vscjava.vscode-java-pack
• vscjava.vscode-gradle
• richardwillis.vscode-gradle-extension-pack
• naco-siren.gradle-language
• dgileadi.java-decompiler

Maven vs Gradle

Package management

Setup spring MVC project

• Init new project: https://start.spring.io/
• Code examples: https://github.com/spring-io/initializr

Command

# build
./gradlew build
# start
./gradlew bootRun

Basic spring keywords

• @Autowired
• @Component
• @Service
• @Repository
• @Configuration
• @Bean

Project structure

├── annotation
│   └── build custom annotation
│   └── aop usage
├── config
│   ├── construct a bean
│   └── consts
├── controller
│   └── build a controller
├── dao
│   └── build dao object
├── dto
│   ├── build dto object
├── exception
│   └── construct a custom exception (Exception vs RuntimeException)
├── factory
│   └── factory pattern
├── filter
│   └── global exception handler filter
├── helper
│   └── helper vs factory
├── manager
│   └── manager layer
├── provider
│   └── build a custom service provider
├── repository
│   └── access to database with repo layer
├── RoadmapApplication.java
├── service
│   └── service class
└── util
    └── utils

Spring libs (servlet containers + api)

• Spring security
• Spring MVC (web)
• Spring Data (JDBC, JPA)

Exercises

Concatenate String

/**
  * Return all numbers x <= n < y concatenated with "_" character
  * @param x
  * @param y
  * @return
  */
public String concatenate(Integer x, Integer y);

Array list test

This is a valid solution? If not reimplement it

List<String> data = new ArrayList<String>(Arrays.asList("testData1", "testData2", "testData2", "testData3"));

System.out.println(data);

for (String d : data) {
    if (d.equals("testData2")) {
        data.remove(d);
    }
}

System.out.println(data);

Ascii art

Print the following ascii art

[]#########
@][########
@@][#######
@@@[]######
@@@@][#####
@@@@@][####
@@@@@@[]###
@@@@@@@][##
@@@@@@@@][#
@@@@@@@@@[]

Long test

Think about it and fix it...

Long test1 = Long.valueOf(113L);
Long check1 = Long.valueOf(113L);

Long test2 = Long.valueOf(2500L);
Long check2 = Long.valueOf(2500L);

if (test1 == check1) {
    System.out.println("OK");
} else {
    System.out.println("KO!");
}

if (test2 == check2) {
    System.out.println("OK");
} else {
    System.out.println("KO!");
}

Decimal test

Think about it and fix it...

float a = 0.01F;
float b = 0.05F;
float c = 0.06F;

System.out.println((a + b) == c);

Leader test

Write a program to print all the LEADERS in the array. An element is leader if it is greater than all the elements to its right side. And the rightmost element is always a leader.elementi alla sua destra

/* input data */
int arr[] = { 10, 8, 14, 23, 15, 0, 9 };
/* expected result [23, 15, 9] */

Custom List

Create the structure "CustomList" with the possibility to save elements of the same type. Custom List can grown in size.

Class must contains

• Constructor/s
• public function "printAll" with the purpose of printing all elements in the list
• public function "push" with the purpose to insert an element as last one

Requirement: The CustomList class cannot contains data structure as Array or List

Add to List

Implement it

public class AddToListClass {
    /**
     * This function creates a new "List" of Integers, and adds to it a range of numbers included between 0 and "maxNumber".
     * "threadNumber" describes the number of threads which will perform this task at the same time (each one should insert a range). 
     * If threadNumber is more than 1, insertion order is not guaranteed.
     * 
     * Examples
     * List<Integer> res = addToList(10, 1); //[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
     * List<Integer> res = addToList(10, 2); //[0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9]
     * 
     * @param maxNumber
     * @param threadNumber
     * @return
     * @throws Exception
     */
    private static List<Integer> addToList(int maxNumber, int threadNumber) throws Exception {
        /* implement it.. */
        return null;
    }

    public static void main(String[] args) {
        try {
            int maxNumber = 10;
            int threadNumber = 1;
            long start = System.currentTimeMillis();
            List<Integer> res = addToList(maxNumber, threadNumber);
            long end = System.currentTimeMillis();
            System.out.println("Total time: " + (end - start) + "ms");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Mini project

@see exercises/mini-project.txt

Reactive stack

Differences and usage

Spring libs (netty containers + streams)

• Spring security reactive
• Spring WebFlux
• Spring Data Reactive(r2dbc, redis, mongo)