1. Week 1 - Friday
COMP 1600

2. Last time What did we talk about last time?
Finished discussing hardware
Our first Java program

3. Project 1

4. Questions?

5. More Java Syntax

6. Semicolons
In Java, like C, C++, and many other languages, we separate different statements with a semicolon ( ; )
If we want to do a number of statements, we just type them in order, with a semicolon after each one

7. Sequencing
For example, instead of one print statement, we can have several:
Each statement is an instruction to the computer
They are printed in order, one by one
System.out.println("Hello, world!");
System.out.println("Hello, galaxy!");
System.out.println("Goodbye, world!");

8. Case Sensitivity Java is a case sensitive language
Class is not the same as class
System.out.println("Word!"); prints correctly
system.Out.Println("Word!"); does not compile

9. Whitespace
Java generally ignores whitespace (tabs, newlines, and spaces)
is the same as:
You should use whitespace effectively to make your code readable
System.out.println("Hello, world!");
System.out.
println( "Hello, world!");

10. Comments Programs can be confusing
Sometimes you want to leave notes for yourself or anyone else who is reading your code
The standard way to do this is by using comments
Although comments appear in the code, they do not affect the final program

11. Comments There are two kinds of comments (actually 3)
Single line comments use //
Multi-line comments start with a /* and end with a */
System.out.println("Hi!"); // this is a comment
System.out.println("Hi!"); /* this is
a multi-line
comment */

12. What we know Java is a large, complex language
Even so, there are only a few tasks that you can ask it to do
You have already learned:
Sequencing
Basic output

13. Where we are headed
There are not that many other things you can tell Java to do
Storing numbers and text
Basic mathematical operations
Choosing between several options
Doing a task repetitively
Storing lists of things
More complicated input and output
Naming a task so that you can use it over and over again
That's basically it

14. Software Development

15. What is programming again?
The process of giving computers very detailed instructions about what to do
How do we do that exactly?
First, we need a programming language like Java
How do we turn a set of instructions written so that a human can read them into a set of instructions that a computer can read?
Magic, of course!

16. First, let's talk about languages
There are many different programming languages:
Java
C/C++ ML
…thousands more
Each has different advantages in different situations

17. High vs. low We can classify languages as high or low level
High level languages allow you to give more abstract commands that are more like human thought processes or mathematics
Low level languages are closer to the computer world and give explicit instructions for the hardware to follow
Python
Java
C++ C
Assembly Language
Machine Code
Low
High

18. Compilers
We use a program called a compiler to turn a high level language into a low level language
Usually, the low level language is machine code
With Java it's a little more complex

19. How does that work in general?
Computer!
Solve a problem;
Compile
Execute
Source Code
Machine Code
Hardware

20. What's the issue with Java?
Java is more complicated
Java runs on a virtual machine, called the JVM
Java is compiled to an intermediate stage called bytecode, which is platform independent
Then, the JVM runs a just-in-time compiler whenever you run a Java program, to turn the bytecode into platform dependent machine code

21. Compilation and execution for Java
class A {
Problem p;
p.solve(); }
Compile
JVM
Execute
Java
Source
Code
Java Bytecode
Machine Code
Hardware
Platform
Independent
Platform
Dependent

22. Let's review the steps we'll use
Write a program in Java
Compile the program into bytecode
Run the bytecode using the JVM (which automatically compiles the bytecode to machine code)

23. Software development
Often goes through phases similar to the following:
Understand the problem
Plan a solution to the problem
Implement the solution in a programming language
Test the solution
Maintain the solution and do bug fixes
Factor of 10 rule!

24. Data Representation

25. Binary Hardware
You have heard people talking about all the 1's and 0's inside of a computer
What does that all really mean?
Using semiconductor physics, we can make a tiny little piece of a microchip be in one of two states, say, OFF and ON, like a switch
If we say that OFF is 0 and ON is 1, then, by using a lot of these switches, we can represent a lot of 1's and 0's

26. Binary Representation
What do we do with those 1's and 0's?
To begin with, we represent numbers
How many of you have heard of base 10?
How many of you have heard of base 2?
What's the definition of a number system with a given base?

27. Base 10 (decimal) numbers
Our normal number system is base 10
This means that our digits are: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9
Base 10 means that you need 2 digits to represent ten, namely 1 and 0
Each place in the number as you move left corresponds to an increase by a factor of 10

28. 3,482,931 Base 10 Example Ten thousands Hundreds Millions Ones Hundred
Tens

29. Base 2 (binary) numbers The binary number system is base 2
This means that its digits are: 0 and 1
Base 2 means that you need 2 digits to represent two, namely 1 and 0
Each place in the number as you move left corresponds to an increase by a factor of 2 instead of 10

30. 11111100011 Base 2 Example Sixty fours 256's Sixteens Fours 1024's
Ones
512's
128's
Thirty twos
Eights
Twos

31. So, what's the value? =
1∙ ∙29 + 1∙28 + 1∙27 + 1∙ ∙25 + 0∙24 + 0∙23 + 0∙22 + 1∙21 + 1∙20 = =
2019

32. The good news
You don't actually have to worry about doing binary conversions when you are coding Java
You should know this information because it explains how Java is different from math
In math, you can talk about an arbitrarily large number
In Java, each number is stored with a specific number of binary digits
There are limits on how big (or small) a given number can be

33. Upcoming

34. Next time…
We'll talk more about data representation

35. Reminders Read Chapter 3 No class on Monday!
No lab assignment on Tuesday, but you can come to ask questions or get started on Project 1
Interested in coaching 7-18 year old kids in programming?
Consider working at theCoderSchool
For more information:
Visit
Contact Kevin Choo at
Ask me!