My goal is to quickly learn and then dive into building a simple CRUD project with Spring Boot 3.
Here’s a summary of the prerequisites:
- Beginner Java Experience
- Java 17 JDK
- Java Build Tools (Maven or Gradle), with a preference for Maven
Install in WSL2
sudo apt update
sudo apt search jdk
sudo apt install openjdk-17-jdk
java --version
javac --versionJDK stands for Java Development Kit, which includes the code compiler JAVAC and other tools like the runtime environment JRE.
JAVAC compiles .java files into .class bytecode files, which are then executed by JRE. The Java Virtual Machine (JVM) in JRE translates bytecode into machine code for execution on different computer devices, enabling Java’s cross-platform capabilities.
Hello World
Firstly, install VS Code and Extension Pack for Java.
Create our first HelloWorld.java file:
- Each file consists of a class with a name matching the file
- A fixed-format main method, which is the program’s entry point
- Compile with
javac HelloWorld.javato generate bytecode - Run with
java HelloWorldto execute the bytecode - Alternatively, use the Run command on the main method via the VS Code extension
class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}Types and Variables
int num1 = 5;
double num2 = 10.2;
double num3;
num3 = 11.1;
final int num4 = 10; // immutable
char letter = 'D';
boolean bool = true;
String site = "mancuoj.me";
// other types: byte short long floatint[] a1;
int[] a2 = {1, 2, 3};
int[] a3 = new int[]{1, 2, 3};
int[] a4 = new int[3];
a4[0] = 1;
a4[2] = 2;
a4[3] = 3;Flow Control
int k = 15;
if (k > 20) {
System.out.println(1);
} else if (k > 10) {
System.out.println(2);
} else {
System.out.println(3);
}
// switch case and ternary operator ? : are also availableint[] numbers = {1,2,3,4,5};
for (int i = 0; i < 5; i++) {
System.out.print(numbers[i]);
}
// or
for (int number: numbers) {
System.out.print(number);
}
// break and continue are also availableint count = 0;
while (count < 5) {
System.out.print(count);
count++;
}
// do-while loop is also availableException control with try, catch, and finally is also present. Let’s stick to the basic syntax for now.
Object-oriented concepts such as classes, constructors, inheritance, polymorphism, overloading, and overriding have extensive discussions, but I’ll keep it brief.