Hello Operator. Mac OS

Apr 26, 2021 If your Mac is using an earlier version of any Mac operating system, you should install the latest Apple software updates, which can include important security updates and updates for the apps that are installed by macOS, such as Safari, Books, Messages, Mail, Music, Calendar, and Photos. Create a new Mac project. First you need to launch your XCode. Create a new project. From the menu there, select Create a new Xcode project. This action will pop up a new window. From the new window you need to select the option MacOS and then navigate to the Application panel. From there you can choose the App option. How to Install Hello Operator for Windows PC or MAC: Hello Operator is an Android Communication app that is developed by devlib.se and published on Google play store on NA. It has already got around 10000 so far with an average rating of 4.0 out of 5 in play store. So here we'll make a command line operating system. As we saw the previous code, the code just writes some text on screen via Console.WriteLine function. Now we will write a OS where the user gives the input and the computer processes it. So, lets make a code which prints Hello User! 'vtable for CORE::NegRep', referenced from: CORE::Expr::operator- const in hello-really-exact.cpp.o NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.

Hello Operator?

Before we jump into the switches we use in our day to day lives at the office. I would like to take you back again to a time when we had telephone operators who would “switch” our calls for us. These operators had the job of picking up any calls that would come in. You would tell them who you are trying to reach and they would connect your line by physically moving a cable from one port on the switchboard to the port of the person you are calling. Their phone will ring and now you are able to have a telephone conversation.
I want you to remember the concept of the operator having to take a physical wire and connect it to a different port as we will be making our own switches do this for us in a similar fashion automatically for us as we start discussing the network switch next.

The Network Switch

Now what is a switch and what does it do? Similar to the call operators it is a central point where cabling goes into (physical) in order to receive frames or “Signals” that are then switched out of the correct ports, switches are an evolution of networking technology which is a great advancement from things such as hubs as well as bridges, the switch is smart enough to switch traffic specifically on a port basis where only the port where the recipient is connected to will receive the frames and the sender will receive any return traffic back, things such as hubs would broadcast the traffic out of all the ports causing problems such as increased network traffic as well as major security concerns as everyone would receive your data.
The process a switch follows is quite straight forward and I will quickly list the details here while we reference the OSI Model as well.
1) The switch will receive a frame on one of its ports and this frame will contain a destination and source MAC-address.
2)The switch will put an entry in its CAM Table or MAC-Address table of which port the frame came from and it will do a lookup against the MAC-Address table if the destination MAC-Address has been learned.
3)If the destination MAC-Address has not yet been learned the switch will send a broadcast message out (an ARP) of all of its ports to try and learn the MAC-Adress.
4)If the destination MAC-Address has been learned the frame will be sent out of the port where the MAC-Address has been learned if no MAC-Address is learned the frame will be dropped.
That is the base function the switch has, it is there to learn MAC-Addresses and switch the traffic in and out of ports, we also have additional features to talk about such as VLANs where the switch can partition some of its ports into different broadcast domains, meaning if the switch receives a frame with a VLAN tag added to the header it will only forward the frame out ports that also have this same VLAN tag configured to it.

Media Access Control Address

A Media Access Control Address or for short a MAC-ADDRESS. This is a physical 48bit address that is burned into each and every NIC when manufactured. These addresses will contain information on the OUI (Organizational Unique Identifier) as well as NIC specific information, think of the OUI as the vendor where Cisco, Juniper or Mikrotik devices will have their own unique 24bit address added to the front of each MAC-Address which serves as proof that this hardware belongs to this vendor.
Think of the MAC-ADDRESS as the IP address that switches use to communicate and that switches transfer frames by sending them out of a port for a specific MAC-ADDRESS, this is all pure Layer 2 communication.

Virtual Local-Area-Network (VLANs)

If you’re new to networking then the idea of VLANs might confuse you a little however, I will do my best to explain what a VLAN is in the easiest terms possible. VLANs allow us a way to assign our switch ports into different broadcast domains. VLANs also follow a standard called 802.1Q. If you recall I mentioned that a switch will send a broadcast message whenever it is doing a lookup for a MAC-ADDRESS. When we start adding VLANs to the Layer 2 equation the lookup will only be done on the broadcast domain that the frame was received so if you have a Laptop in VLAN1 trying to send a frame, the switch will receive the frame and only send the frame out of ports that also have VLAN1 assigned to it, the machines in VLAN2 will not receive any broadcast messages and no frames will be passed between machines in different VLANs.
This is useful for segmenting your network and could potentially also be a security requirement for the company you work for, where machines in your finance department may only see other finance department machines. Another use for this would be to split up customer networks as well, you could potentially use the same switch for many different customers and none of their frames will be exchanged with each-other due to how VLANs function.

Hello Operator. Mac Os Catalina

Conclusion

You have now learned how switches work in our day to day lives and how layer 2 frames are passed between ports as well as what a Mac-Address is and what VLANs are, this is a very important fundamental for any network engineer as this plays a big part in your daily work, the bigger the networks you support the more VLANs you will start seeing and the more switches you will be supporting. I hope this has been informational for you and that you have learned something new.
Please apply to our newsletter for any new blogs that are posted as well as sign-up to my youtube channel to view any related vlogs on any of these subjects.

Hungry for more?

Why not check out the follow-up post on routers and routing
https://thenetworkberg.com/routers-and-routing to get more insight on how routing works or check out the previous article for a refresher on host-to-host communication on what a network is
https://thenetworkberg.com/networking-basics

This DrJava-based Java programming environment is no longer being supported(because DrJava in no longer being actively developed and DrJava is incompatible with Java 11).It has been replaced by the following IntelliJ-based programming environment forMac OS X.

This document instructs you on how to set up our Java programming environment for your Mac OS X computer. It also provides a step-by-step guide for creating, compiling, and executing a Java program using either DrJava or the Terminal.All of the software used is freely available.

You will need an Intel-based Mac runningMac OS X 10.8 (Mountain Lion) to Mac OS X 10.13 (High Sierra).

You can defer steps 4–6 until Section 1.5 of the textbook.

0. Install the Programming Environment

Our installer downloads, installs, and configures the Java programming environment you will be using, including DrJava, and the standard libraries from our textbook.

Log in to the user account in which you will be programming.Your account must have Administrator privileges (with a non-blank password)and you must be connected to the Internet.
Install Oracle's implementation of the Java Platform, Standard Edition Development Kit (JDK 8).Do not install either JDK 9 or JDK 10, as they are currently incompatible with DrJava.
- Browse toJava SE Development Kit 8u171.In the first table, check Accept License Agreementand the click jdk-8u171-macosx-x64.dmg,which corresponds to the entry for Mac OS X.The exact verison 8u171 is not essential.
- Double click the downloaded file jdk-8u171-macosx-x64.dmg to begin the installation.Enter your OS X password when prompted.We recommend all of the default options.
- Delete jdk-8u171-macosx-x64.dmg.
To install,
- Download introcs.zip to the Desktop;double-click it to unzip (if necessary). This creates introcs.app. Security and Privacy -> General -> Allow applications downloaded from: Anywhere.
  To enable this option, you may need to click the lock in the lower left-hand corner(and type your password when prompted).-->
- Double-click introcs.app to perform the installation.If you receive a warning that introcs.app is an applicationdownloaded from the Internet, click Open.
- Enter your OS X password when prompted.
If the installation succeeds, you will see the following:
- A Terminal window containing approximately thisexecution log.
- A Standard Drawing window containing a red bullseye and a textbook graphic.
Delete introcs.zip and introcs.app.

1. Create the Program in DrJava

Now you are ready to write your first Java program.You will develop your Java programs in an application called DrJava.DrJava features many specialized programming tools including syntax highlighting,bracket matching, auto indenting, and line numbering.

The installer creates a shortcut to DrJava on the desktop.Double-click it to launch DrJava.If you receive a warning about incoming network connections,click Allow.
In the main DrJava window, type the Java programHelloWorld.java exactly as it appears below. If you omit even a semicolon, the program won't work. As you type, DrJava does the indenting for you.
Finally, click the Save button to save the file, using the name HelloWorld.java.The filename is case sensitive and must exactly match the name of theclass in the Java program.

2. Compile the Program in DrJava

It is now time to convert your Java program into a form more amenable for execution on a computer. To do this, click the Compile button.If all goes well, you should see the following message in the Compiler Outputpane at the bottom:

Mac Os Catalina

If DrJava complains in some way, you mistyped something.Check your program carefully, using the error messages in the Compiler Output paneas a guide.

3. Execute the Program in DrJava

Now it is time to run your program. This is the fun part.

Type the following in the Interactions pane at the bottom.By convention, we highlight the text you type in boldface. If all goes well, you should see the following message:
You may need to repeat this edit–compile–execute cycle a few times before it works. Ask for help if you can't see the mistake.

Congratulations, you are now a Java programmer!

4. Command-Line Interface with the Terminal

The command-line provides capabilities beyond those available in DrJava,including redirection and piping.You will type commands in an application called the Terminal.

The installer creates a shortcut on the desktop to the Terminal.Double-click it to launch the Terminal.You should see something like:The ~ is shorthand for your home directory /Users/<username>.
To confirm that the Java compiler is installed,type the command in boldface below and check that the results match:It's important that you see the number 1.8for the Java version number, but the rest is not critical.
To confirm that you the Java interpreter is installed, typethe command in boldface below and check that the results match:Again, it's important that you see the number 1.8for the Java version number, but the rest is not critical.

5. Compile the Program from the Terminal

You will use the javac command to convert your Java program into a form more amenable for execution on a computer.

From the Terminal, navigate to the directory containing HelloWorld.java,say ~/Desktop/hello,by typing the cd (change directory) commands below:The ~ is shorthand for /Users/<username>.
Compile it by typing the javac command below:Assuming the file HelloWorld.java is in the current working directory,you should see no error messages.
To make our textbook standard libraries accessible to Java,use the command javac-introcs instead.For example,BouncingBall.javais a program that uses our standard drawing library.After downloading the file to the current directory,you can compile it with the following command:

6. Execute the Program from the Terminal

You will use the java command to execute your program.

From the Terminal, type the java command below.You should see the output of the program.
To make our textbook standard libraries accessible to Java,use the command java-introcs instead. For example, to executeBouncingBall.java(assuming you downloaded and compiled it in the previous step), type the following command:

Troubleshooting

How long should the installer take?Once downloaded, the Oracle Java installer should take about 10 seconds and the introcs.app installer should take about 20 seconds. If you have virus detection software running (such as McAfee Endpoint), each could take 5–10 minutes (or more).

The installer didn't work on my machine. What should I do?Check out the following three Q+As. If these don't resolve the issue,please contact a staff member to identify what went wrong.

When I run the installer, the terminal window just waits after asking for a password.But, I don't even have a password-enabled account.You must have a non-blank password. Here are instructions forresetting a user's password.

When I run the installer, I get the error message'bash: /Volumes/Macintosh: No such file or directory'.Your user account and OS must be on the same volume.

When I run the installer, I get an error like bash: /private/var/folders/70/n8stth1d1x33hrw8n07kf1280000gn/T/AppTranslocation/45FC25B7-17E3-46DF-AC27-9A7EF56DDFD3/d/algs4.app/Contents/Resources/launcher.sh: No such file or directory.What should I do? This is likely due to OS X Sierra path randomization.Use the Finder to move introcs.app to some other folder and try again.

What does the installer do?In short, it downloads, installs, and configures Checkstyle, Findbugs, and DrJava, and the textbook standard libraries.Here is a more detailed list:

Checks that Java is installed.
Downloads the textbook standard libraries fromstdlib.jar.
Downloads the Java wrapper scriptsjavac-introcs andjava-introcs.
Downloads and installsFindbugs 3.0.1from findbugs.zip.Downloads our findbugs configuration file findbugs.xml and wrapper script findbugs-introcs.
Downloads and installsPMD 5.8.1from pmd.zip.Downloads our PMD configuration file pmd.xmland wrapper script pmd-introcs.
Downloads and installsCheckstyle 8.2from checkstyle.zip.Downloads our checkstyle configuration file checkstyle-introcs.xml and wrapper script checkstyle-introcs.
Downloads and installs the latest stable version ofDrJava,from DrJava.zip.Creates a shortcut to DrJava on the Desktop.Downloads and installs the DrJava configuration file fromdrjava-config.txtto /Users/<username>/.drjava.Note that this will overwrite any existing .drjava configuration file.
Tests that the installation succeeded by compiling and executing TestIntroCS.java.

Why does the installer need my password?The installer copies files into /usr/local/bin and/usr/local/introcs,which require superuser privileges.

Hello Operator. Mac Os X

How do I completely uninstall introcs.app?

Delete the directory /usr/local/introcs.
To uninstall DrJava, delete the following two files:
- /Applications/DrJava.app.
- /Users/<username>/.drjava.
To uninstall the Java, Checkstyle, and Findbugs wrapper scripts,delete the following files:
- /usr/local/bin/javac-introcs
- /usr/local/bin/java-introcs
- /usr/local/bin/findbugs-introcs
- /usr/local/bin/pmd-introcs
- /usr/local/bin/checkstyle-introcs
Delete the shortcut to DrJava and Terminal on the Desktop.

What happens if I re-run the installer?It will re-download, install, and configure Checkstyle, Findbugs, DrJava, and our textbook libraries.

Can I use a different version of Java?Any version of Java 8 (either Oracle or OpenJDK) should work fine.Note that DrJava does not currently work with Java 9.

I have both Java 8 and Java 9 installed, but the default version is Java 9. How doI change the default version back to Java 8?To disable Java 9, type the following commands in the Terminal:

Hello Operator. Mac Os 11

You should still be able to use Java 9 by specifying the full path tojavac and java, e.g., Operator.

/Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home/bin/javac.

Why I try to run DrJava, I get the following error message. How should I proceed?

Are you sure that you are using the version of DrJava that was installedby our auto-installer (and not downloaded from the DrJava website)?We suggest deleting any older versions of DrJava and using the one that the auto-installer copied to the /Applications directory.

Can I use a different IDE? Yes you can use another IDE (such as Eclipse) butyou will have to configure the IDE properties yourself (such as the classpath). Reset Interactions.From the Terminal, type Ctrl-c.

When using standard input, how do I signify that there is no more data?If you are typing input in the Terminal or DrJava, type Ctrl-d on its own line.

I successfully compiled HelloWorld.java with javac, but, when I execute,I get the error message'Exception in thread 'main' java.lang.NoClassDefFoundError: HelloWorld'.What am I doing wrong?First, verify that the file HelloWorld.class is in the current directory.Be sure to type java HelloWorld without a trailing .classor .java.-->

Hello Operator. Mac Os 11

When I compile or execute a program in Terminal that uses thetextbook standard library, I get an error that it cannot find the library. How can I fix this?Use the wrapper scripts javac-introcs and java-introcs,which add stdlib.jar to the Java classpath.

Which shell should I use in the Terminal?Bash is the default shell in Mac OS X, but feel free to usewhichever one you prefer.

Where can I learn more about the command line?Here is a short tutorial on thecommand line.