Секреты Java

Class.forName("oracle.jdbc.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "username", "password");
Statement s = con.createStatement();

String sql1 = "CREATE TABLE STUDENT(STUDENTID VARCHAR2(10) PRIMARY KEY,NAME VARCHAR2(20),DEPARTMENT VARCHAR2(10))";
String sql2 = "INSERT INTO STUDENT VALUES('S101','JEAN','CSE')";
String sql3 = "INSERT INTO STUDENT VALUES('S102','ANA','CSE')";
String sql4 = "INSERT INTO STUDENT VALUES('S103','ROBERT','ECE')";

s.addBatch(sql1);
s.addBatch(sql2);
s.addBatch(sql3);
s.addBatch(sql4);

s.executeBatch();
con.commit();
con.close();

implementation 'org.springdoc:springdoc-openapi-ui:1.7.0'

implementation 'org.springdoc:springdoc-openapi-starter-webmvc-ui:2.3.0'

@Tag(name = "Entities")
@RestController
public class Controller {

    @Operation(summary = "Get entity")
    @GetMapping("/")
    public Object get() {
        return "Hello world!";
    }
}

FROM gradle:7.6.0-jdk17
WORKDIR /app
COPY . .
RUN gradle build --no-daemon
EXPOSE 8080
CMD ["java", "-jar", "/app/build/libs/demo-0.0.1-SNAPSHOT.jar"]

docker build -t demo .
docker run -p 8080:8080 demo

REPOSITORY  TAG     CREATED        SIZE
demo        latest  9 seconds ago  889MB

CONTAINER ID  IMAGE  STATUS          PORTS                   
e343769f7330  demo   15 seconds ago  0.0.0.0:8080->8080/tcp 

double first = 0.1;
double second = 0.2;
double result = first + second;

System.out.println(result); // Выводит 0.30000000000000004

var first = new BigDecimal("0.1");
var second = new BigDecimal("0.2");
var result = first.add(second);

System.out.println(result); // Выводит 0.3

META-INF/
    MANIFEST.MF
com/
    myapp/
        MyApp.class

META-INF/
    MANIFEST.MF
WEB-INF/
    web.xml
    jsp/
        myApp.jsp
    classes/
        static/
        templates/
        application.properties
    lib/
        // different *.jar libs

public void someMethod() throws IOException {
    try {
        // код, который может выбросить IOException
    } catch (IOException e) {
        // возможно, выполнить какую-то обработку
        throw e; // проброс исключения дальше
    }
}

for (initialization; condition; update) {
    // тело цикла
}

int[] numbers = {1, 2, 3, 4, 5};
for (int i = 0; i < numbers.length; i++) {
    System.out.println(i + ": " + numbers[i]);
}

for (type element : collection) {
    // тело цикла
}

int[] numbers = {1, 2, 3, 4, 5};
for (int number : numbers) {
    System.out.println(number);
}

while (condition) {
    // тело цикла
}

String code = UUID.randomUUID().toString();
boolean isCodeExists = repo.isCodeExists(code);
while (isCodeExists) {
    code = UUID.randomUUID().toString();
    isCodeExists = repo.isCodeExists(code);
}
repo.saveCode(code);

do {
    // тело цикла
} while (condition);

String command;
do {
    command = readCommand();
    doCommand(command);
} while (!"EXIT".equals(command));

public class MainClass {
 public static void main(String args[]) {
  TestClass a = new TestClass();
  a.a();
  a = null;
  a = new TestClass();
  a.a();
  System.out.println("!!! done");
 }
}

public class TestClass {
 public void a() {
  System.out.println("!!! a() called");
 }

 @Override
 protected void finalize() throws Throwable {
  System.out.println("!!! finalize() called");
  super.finalize();
 }
}

!!! a() called
!!! a() called
!!! done

public class MainClass {
 public static void main(String args[]) {
  TestClass a = new TestClass();
  a.a();
  a = null;
  System.gc(); // Принудительно зовём сборщик мусора
  a = new TestClass();
  a.a();
  System.out.println("!!! done");
 }
}

!!! a() called
!!! a() called
!!! done
!!! finalize() called

!!! a() called
!!! a() called
!!! finalize() called
!!! done

public class Test {

    public static int VAL;

    {
        VAL = 5;
    }

    public Test() {
        VAL = 10;
    }

    public static void print() {
        System.out.println(VAL);
    }

}

public class Quest {
    public static void main(String[] args) {
        Test.print();
    }
}