All the versions of JDK come bundled up with the JRE (Java Runtime Environment). This way, a user doesn’t have to download and install JRE on their PC separately.

https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-4.html

check the major version for your JAVA code (the java class file)

65 is the major version , correspond to JAVA-21

you HAVE TO READ RUNNING.TXT , located in tomcat/

JRE_HOME or JAVA_HOME , required , not both , so simple solution , just delete JRE_HOME , altough some servlet tutorials (almost all) lead you to set up both .

if you find is neccesary set up both of them , this is the proccess , at final i give you some advices if nothing of these works ….

check our environments variables , this is the reason of our problem

we can comprobe just looking in our apachetomcat initialization

to solve you should JAVA_HOME == JRE_HOME , i mean have to be the same both jdk-21

JRE_HOME= xxx.yyyy.zzzz/jdk-21

check the current Java version load by server in in manager/html

admi user admin password is not the default one , have to config in tomcat-users.xml

  <user username="admin" password="admin" roles="manager-gui,manager-script,manager-jmx,manager-status,admin-gui,admin-script"/>

now , launch again tomcat server

install apache tomcat as a SERVICE is not the same that execute by startup.bat , just for test purpose you unistall the service one , and download a zip one , then launch it using startup.bat located at bin folder , indeed you can use both , just need to change the ports , but i suggest you foor test purpose unistall one of them

interface MyInterface {
	void sayHello();
}

class ClassOne {
	static void methodThatCallInterfaceMethod(MyInterface i) {
		i.sayHello();
	}
}

class ClassTwo implements MyInterface {
	static void sayGoodBye() {
		System.out.println("hi - for METHOD REFERENCE CALLING");
	};

         @Override
	public void sayHello() {
		// TODO Auto-generated method stub
		System.out.println("Good Morning FROM CASS THAT DIRECTLY IMPLEMENTS INTERFACE ");
	}

	MyInterface getMyInterface() {
		return this;
	}
}

class ClassThree {
	static ClassTwo getInstanceOfClassTwo() {
 		return new ClassTwo();
	}
}

public class Main implements MyInterface {
	public static void main(String[] args) {
		Main InstanceOfMain = new Main();
		//METHOD 1
		InstanceOfMain.methodThatServeAsABridgeToExecuteinMainStaticMethod();
		//METHOD 2
		ClassOne.methodThatCallInterfaceMethod(new Main());
		//METHOD 3
		ClassOne.methodThatCallInterfaceMethod(new MyInterface() {
			@Override
			public void sayHello() {
				// TODO Auto-generated method stub
				System.out.println("Good morning from INNER CLASS");
			}
		});
		//METHOD 4
		ClassOne.methodThatCallInterfaceMethod(() -> System.out.println("Hi from LAMBDA IMPLEMENTATION"));
		//METHOD 5
		ClassOne.methodThatCallInterfaceMethod(ClassTwo::sayGoodBye);
		ClassTwo InstanceClassTwo = new ClassTwo();
		//METHOD 6
		ClassOne.methodThatCallInterfaceMethod(InstanceClassTwo);
		//METHOD 7
		ClassOne.methodThatCallInterfaceMethod(InstanceClassTwo.getMyInterface());
		//METHOD 8
		ClassOne.methodThatCallInterfaceMethod(ClassThree.getInstanceOfClassTwo());
		MyInterface instanceCreatedToStoreAnnonymousInnerClass = new MyInterface() {

			@Override
			public void sayHello() {
				// TODO Auto-generated method stub
				System.out.println("hi from ANNONYMOUS INNER CLAS ASIGNED TO VARIABLE");
			}

		};
		ClassOne.methodThatCallInterfaceMethod(instanceCreatedToStoreAnnonymousInnerClass);
		ClassOne.methodThatCallInterfaceMethod(()->InstanceOfMain.methodInsideMainClass());
		
	}
	void methodInsideMainClass () {
		System.out.println("hi from CLASS INSIDE MAIN CLASS");
	};

	void methodThatServeAsABridgeToExecuteinMainStaticMethod() {
		ClassOne.methodThatCallInterfaceMethod(this);
	}

	@Override
	public void sayHello() {
		// TODO Auto-generated method stub
		System.out.println("hi from Main INSIDE CLASS");
	}
}

SQL Developer help enter a substitution variable

«Insert into CSE_DEPT.COURSE (COURSE_ID,COURSE,CREDIT,CLASSROOM,SCHEDULE,ENROLLMENT,FACULTY_ID) values (‘CSE-334′,’Elec. Measurement & Design’,3,’TC-212′,’T-H: 11:00-12:25 PM’,25,’H99118′);»
In SQL , » &» is interpreted as the beginning of a substitution variable .

3 possible solutions :

SET ESPACE ‘\’ , and use ‘\’ to scape & in you code exp: \&
SET SCAN OFF , disable scanning for substitution variables

SET DEFINE OFF; turn off substitution completely

node -v ### to verify correct installation

npm -v

right click on shell icon > properties > «start in»

this is the deafualt starting «start in» folder : «%HOMEDRIVE%%HOMEPATH%»

after instal vim , there is a problem to launch vim from command prompt

we have to add a path to our user variables , first have to find folder where is our vim executable …

go to «environment variables»

edit «path» in user variables , ADD the folder where is you vim executable (there many other paths inside )

to flush/clean DNS , have to know your DNS resolver service

cat /etc/resolv.conf

«systemd-resolve» and «systemd-resolved» ARE NOT THE SAME

«systemd-resolve» is a command line tool for interacting with the «systemd-resolved» service and «systemd-resolved» is the actual DNS resolver service

sudo systemd-resolve –flush-caches

sudo systemctl restart systemd-resolved

these two commands fusl complety DNS cache ,