Elissa Redmiles

Use slide puzzles to help students understand how packets get reassembled when they reach their destination because students need help creating a mental model and are often are amazed and confused by this process.

cstt — Wed, 27 May 2015 19:25:41 +0000

Use slide puzzles to help students understand how packets get reassembled when they reach their destination because students need help creating a mental model and are often are amazed and confused by this process. cstt Wed, 05/27/2015 - 12:25 Share Use slide puzzles to help students understand how packets get reassembled when they reach their destination because students need help creating a mental model and are often are amazed and confused by this process. with Facebook Share Use slide puzzles to help students understand how packets get reassembled when they reach their destination because students need help creating a mental model and are often are amazed and confused by this process. with Twitter

Students are often amazed that this complex re-assemblage happens to all information!
Provide an explanation of how the internet works focusing on sending pictures, then follow up with a demonstration/activity using slide puzzles to help students develop a concrete understanding for this idea.

This explanation and activity focus on how a full picture gets broken up into packets and needs to be reassembled.

Explanation:

When photographs (or other content) is sent over the internet from computer 1 to computer 2, it is broken up into discrete pieces called packets.
These packets might not arrive at computer 2 in the same order they left computer 1 in.
Therefore, when computer 2 gets all the packets, it has to put all the pieces together like a puzzle.

Activity:

Have a picture puzzle to be used for this class ready.

Note: You can use a small jigsaw puzzle, a slide-picture puzzle, or even a picture you cut with scissors.
Elissa typically cuts a picture with scissors.

Pick one student to be computer 1 and one student to be computer 2.
Give the slide picture puzzle, in the complete and correct order to computer 1.
Tell the class that computer 1 is going to send this picture to computer 2, just like in your earlier explication.
If you have 8 pieces, assign 8 students. to each walk one piece of the picture from computer 1 to computer 2.

Note: change the number of student volunteers to match the number of puzzle pieces there are.

Have each of these 8 student pick up a random piece of the puzzle and walk that one piece of the picture from computer 1 to computer 2.
Have computer 2 work to put put the pieces of the puzzle back together.

If you can, project the puzzle arriving at computer 2 and being reassembled so the whole class can see.

Emphasize to the class that when these pieces get to computer 2, that person has to put them together again to make a picture, just like when the jumbled packets arrive through the internet.

Have students act out packet routing to learn about how information moves through the Internet in a way that is easy for them to understand and visualize.

cstt — Wed, 27 May 2015 19:18:20 +0000

Have students act out packet routing to learn about how information moves through the Internet in a way that is easy for them to understand and visualize. cstt Wed, 05/27/2015 - 12:18 Share Have students act out packet routing to learn about how information moves through the Internet in a way that is easy for them to understand and visualize. with Facebook Share Have students act out packet routing to learn about how information moves through the Internet in a way that is easy for them to understand and visualize. with Twitter

This activity, borrowed from Jan Plane at University Maryland, College Park, works especially well with younger students.
Activity:

Assign all student to one of four roles:

Routers
Packets
Clients
Servers

Tell the students what each role is supposed to do.
Give Packet students pieces of papers.
Next, Client students send the Packet students to a particular series of Routers.

Say Client student 1 send’s every other Packet student to Router student A or Router student B.

So a Packet student gets sent to Router student A, then the next Packet student gets sent to Router B, and then the next to Router A, and so on and so forth.

Then Router students send the Packet student to another Router student.

Say Router A sends a Packet student to Router D.
The Packet student walks over to Router D and that Router directs them to a Server.
The Packet student gives the Server their piece of paper.
The Server makes a modification to the paper (perhaps they’ll draw on it).
Then the Server gives the paper back to the Packet and send the Packet to a Router.
The Router sends them back to the Client.

Note: Depending on the number of students, you can make this more or less complex.

Force students to explore inheritance and the Java APIs for ArrayList by writing code that HAS-A ArrayList or IS-A ArrayList.

cstt — Wed, 27 May 2015 00:26:22 +0000

Force students to explore inheritance and the Java APIs for ArrayList by writing code that HAS-A ArrayList or IS-A ArrayList. cstt Tue, 05/26/2015 - 17:26 Share Force students to explore inheritance and the Java APIs for ArrayList by writing code that HAS-A ArrayList or IS-A ArrayList. with Facebook Share Force students to explore inheritance and the Java APIs for ArrayList by writing code that HAS-A ArrayList or IS-A ArrayList. with Twitter

Students often don’t understand the motivation for Java inheritance and also have difficulty navigating Java API pages.

You can encourage students to explore the Java API using either of the two activities:

Activity A: Have students write a Java Class that HAS-A ArrayList
Activity B: Have students write a Java Class that IS-A ArrayList

Activity A: HAS-AN ArrayList

Assign students to write a class that has a Java ArrayList

This goal is to encourage them to explore Java APIs and call provided methods.

Ask students to look up available methods in java documentation for ArrayList and use those methods to implement the library methods

For example, you could have students write code to show them that you can build on all of the functionality of the Java library classes like the code shown below.

import java.util.ArrayList; public class Library{ public ArrayList books; public void addBook(Book b){ books.add(b); } }

Activity B: IS-AN ArrayList

Assign students to create a class that extends Java ArrayList to encourage them to explore Java APIs and call provided methods.

For example, you could have students write code like the code shown below to show students that you can build on all of the functionality of the parent class!

import java.util.ArrayList; public class Library extends ArrayList { public void add(Book b) { super.add(b); // calling the ArrayList method } }

Note from CS Teaching Tips Team: This has the unfortunate consequence that every public method provided by ArrayList is also available for your new class, which is probably not something you’d want.

Walk students through clicking on links in Java Docs to figure out unknown words and concepts (like iterable) by exploring the detailed explanation; plus the AP test expects students to read Java Docs online.

cstt — Tue, 26 May 2015 18:57:04 +0000

Walk students through clicking on links in Java Docs to figure out unknown words and concepts (like iterable) by exploring the detailed explanation; plus the AP test expects students to read Java Docs online. cstt Tue, 05/26/2015 - 11:57 Share Walk students through clicking on links in Java Docs to figure out unknown words and concepts (like iterable) by exploring the detailed explanation; plus the AP test expects students to read Java Docs online. with Facebook Share Walk students through clicking on links in Java Docs to figure out unknown words and concepts (like iterable) by exploring the detailed explanation; plus the AP test expects students to read Java Docs online. with Twitter

Model how to read a Java API for students by showing how you would click on the names of classes and interfaces you don’t know to investigate what methods they have.
Prompt students to explain what a particular method shown in the Java API returns.

Have them write on a piece of paper how they would call this method.

Have students act out diagrams they create of the stack and heap to extend this common drawing exercise and help them strengthen their mental models.

cstt — Tue, 26 May 2015 18:36:42 +0000

Have students act out diagrams they create of the stack and heap to extend this common drawing exercise and help them strengthen their mental models. cstt Tue, 05/26/2015 - 11:36 Share Have students act out diagrams they create of the stack and heap to extend this common drawing exercise and help them strengthen their mental models. with Facebook Share Have students act out diagrams they create of the stack and heap to extend this common drawing exercise and help them strengthen their mental models. with Twitter

Draw a picture of the stack and the heap in order to help students understand:

what really happens when they write their code.
concepts like "mutable" and "deep vs. shallow copy."

Sometimes students will say they understand the stack and heap diagrams, but they have an ah-ha moment after acting out how variables are passed between methods.
Activity Prep:

Create a paper drawing or cutout of a cat.
You could use something else to represent the variable, the using a cat to represent a cat will help students make the connection.
Create a stack of papers that says "Cat c" to represent the cat drawing.

Activity:

Write the following code on the board:

public static void main(String args[]){ Cat c = new Cat("sam", 9); System.out.println(c); foo(c); System.out.println(c); } public void foo(Cat cat){ cat.moreLives(1); }

Introduce the class to your drawing that is representing "Cat c".
Ask for a volunteer to be the pointer to "Cat c", this student will point to the cat on the board and hold the paper that says "Cat c"
Ask for a volunteer to represent the "foo" method.
Now, have the student pointing to "Cat c" representation, give one "Cat c" card to the student representing the "foo" method.

Make sure the "Cat c" representative is still pointing to the cat on the board.

The "foo" method student will draw a new number of lives on the "Cat c" object.
Then have the student representing foo walk away.

Explain that Strings in Java are a weird-hybrid between a primitive and an Object and as a result they can’t be modified.

cstt — Tue, 26 May 2015 18:17:08 +0000

Explain that Strings in Java are a weird-hybrid between a primitive and an Object and as a result they can’t be modified. cstt Tue, 05/26/2015 - 11:17 Share Explain that Strings in Java are a weird-hybrid between a primitive and an Object and as a result they can’t be modified. with Facebook Share Explain that Strings in Java are a weird-hybrid between a primitive and an Object and as a result they can’t be modified. with Twitter

Draw students’ attention to the fact that Strings are Objects, but, because they can’t be modified, work more like a primitive when you initialize them and when you pass them between methods.
When you initialize a String in Java, it can look very similar to initializing an int!

String s = "cat"; int x = 7;

One way to help students recognize how strings are like Objects is to point out the need for using the keyword new when use the String constructor.

String s = new String("cat");

Use Clock as an example of an abstract class because ALL clocks have the same mechanism for keeping time, a necessary property for an Abstract Class, to provide students with a strong real-world mental model for abstract classes.

cstt — Tue, 26 May 2015 18:06:16 +0000

Use Clock as an example of an abstract class because ALL clocks have the same mechanism for keeping time, a necessary property for an Abstract Class, to provide students with a strong real-world mental model for abstract classes. cstt Tue, 05/26/2015 - 11:06 Share Use Clock as an example of an abstract class because ALL clocks have the same mechanism for keeping time, a necessary property for an Abstract Class, to provide students with a strong real-world mental model for abstract classes. with Facebook Share Use Clock as an example of an abstract class because ALL clocks have the same mechanism for keeping time, a necessary property for an Abstract Class, to provide students with a strong real-world mental model for abstract classes. with Twitter

This is a good example of an abstract class because all clocks have shared functionality.

For example, in the code below, we assume that all classes that extend the abstract class Clock would want to have an int to store hours, minutes, and seconds, and need a tick() method.
The display() method is left as an abstract method for child classes to define since different clocks may use digital or analog displays.
public abstract class Clock{ int h,m,s; boolean AM; public void tick(){ s++; if(s==60){ s=0; m++; } if(m==60){ m=0; h++; } if (h==12){ AM = !AM; } } public void display(); }

Use Car as an example of an interface because students agree on the general behaviors of a car but can only come up with specific instantiations of cars, which provides students with a strong mental model for interface relationships.

cstt — Tue, 26 May 2015 17:58:05 +0000

Use Car as an example of an interface because students agree on the general behaviors of a car but can only come up with specific instantiations of cars, which provides students with a strong mental model for interface relationships. cstt Tue, 05/26/2015 - 10:58 Share Use Car as an example of an interface because students agree on the general behaviors of a car but can only come up with specific instantiations of cars, which provides students with a strong mental model for interface relationships. with Facebook Share Use Car as an example of an interface because students agree on the general behaviors of a car but can only come up with specific instantiations of cars, which provides students with a strong mental model for interface relationships. with Twitter

It is really important to provide students with tangible motivation for interfaces and inheritance.
Activity:

Ask a student to draw a "general car."
They’ll quickly realize (or you’ll point out) that you’re not drawing a general car. Rather they are drawing a specific car! (a Bug, a Jeep, etc.)

Connect this realization to the idea of interfaces.

Make interfaces intuitive by explaining that you can never really have a general car, but there is shared behaviors (i.e. methods) for cars.

Additionally, cars wouldn’t be an abstract class because the internal components of a car might have no similarity.

Then, create sample code for the interface Car and an inheriting class like the following:

public interface Car{ String brand, model; double speed; int xCoord, int yCorod; public void move(); }
public class OffRoadCar implements Car{ boolean bikeRack=true; public void move(){ xCoord++; } }