Lecture 4 Lecture notes and files

Here I will try to post the most important ideas from each lecture. Not all ideas will be posted here. I'll also try to include useful sample files and examples.

Week 1 1/22-1/25
Wednesday

Your lecturer is named Tim, and he wants you to enjoy this course, learn a lot, and have fun in lecture.
This can be a very hard class. You need to know the rules and be familiar with the website.
Programs are strings simple commands that are put together to make neat thing happen
Some commands can do many things depending on the input, or parameters, they take.

Friday

I wasn't kidding about pop quizzes--they will come very frequently.
I take your suggestions on how to run this course seriously.
Complicated programs are made of many interacting parts called objects.
Each object has it's own list of abilities, which are called methods.
Various methods have different types of inputs (parameters) and outputs (parameters)

The drawing that only takes a few turtle commands to create is here

Week 2 1/28-2/1
An outline of Chapter 2 by Aneesh is here
Monday

Computer Science is the art, theory, and practice of programming.
High level code is for humans, low-level for machines. A compiler converts the code for us.
Understanding errors is important. There are lots and knowing them helps
To declare a variable, you need a valid type and a valid name
To assign a value, you need a valid variable and a value of the correct type

Wednesday

Each method has a list of parameters (inputs). Each has it's own type.
Methods must be called with the correct number and types of parameters (in the right order) to compile
Methods has a certain type of return value.
Constructors also take parameters
You can hold reasonably sized integers in int. Java doubles are only approximate.

Friday

Be sure to understand compiler errors--what causes them, etc.
The Java API is great gives you all you need to know to understand a class.
Testing code is important--otherwise your code will probably not work
Code is grouped into packages. Code in other packages is accessed through import statements.

The compiler challenge (corrected) is found here. The answers are here.

Week 3 2/4-2/8
Aneesh's outline of Chapter 3 is found here
Monday

Each object of a given class stores its information in instance fields
Inside a class declaration we put instance fields, methods and constructors
The syntax for an instance field includes an access type, a type, and a name
The syntax for methods includes an access type, a return type, a name, a parameter list, and the code to execute
The syntax for constructors includes an access type, the name (the same as the class name), a list of parameters and the code to execute
The syntax for using things and for declaring things is completely different

The class we designed today is here: Team.java
Here is another class Human.java and the associated javadoc
The general syntax for a class is here from Rebecca Hasti
An annotated example class is found here from Will

Wednesday

Local variables are for holding intermediate values
Instance fields hold the data for each Object
Parameters are inputs to functions
Primitive variables (int, double, float, char, short, byte, boolean, long) hold the actual value
Object variables hold a reference to the object

The object practice with the Team class is here
Another explanation of the three types of variables is here from Will
Another explanation of primitive vs. reference is found here

Constructing classes, declaring and writing methods, declaring instance fields

Friday

Choose the right type of number for your job. You may need to cast when you might lose precision.
Operators take some values of a certain type and returns a value of a certain type
Expressions can be chained together as long as we want
Code tracing is an important skill you should be able to do yourself.

Here is a code tracing challenge and the solution from Andrew.
Here's another challenge and another solution from Andrew.

Week 4 2/11-2/15
Monday

final means that the value can't be changed once it is set
static means that the variable or method belongs to the class.
You may call a static method on a class.
Naming constants (often public static final) can make your code easier to read and maintain.

Here is the annotated solution to the in-class Team code-tracing challenge

Wednesday

Scanners are a good way to take input
Scanners are in the java.util package and have useful methods--look them up if you need them
There are lots of great String methods--look them up if you need them
If there is a static variable, all of the instances share that instance
++, +=, -= and -- are increment and decrement functions. Use them as statements, not expressions

Friday

static methods shouldn't be called on instances
Booleans are either true or false
>,<,<=,>=,||,&&,!,==,!= all return booleans
booleans are really valuable types

Week 5 2/18-2/22
Monday

Truth tables are a nice way to represent boolean functions
Boolean expressions can sometimes be simplified by laws of logic
methods can return booleans
== checks only if two Objects are precisely the same in memory
Use .equals() to compare Strings. Same with many other Objects
.equals() often needs to be written to be useful

Wednesday

if statements require booleans as conditions
if statements let us execute code only on a given condition.
If we wish to execute something only if the if statement does not execute, we need an else
You don't need to use braces for ifs and elses, but do it anyway.
else ifs are just a combination of standard if-else syntax

Friday

The one point questions require you to know stuff
Assignments require a variable to exist, but accessible (static? private?), be non-final, match the type of the expression and the expression must compile
Method calls require the object to exist, be initialized, have the method exist, the method be accessible, have the correct number order and types of parameters, and have the parameters compile.
We still have more to review

Week 6 2/25-2/29

Monday

You can review almost all of CS302 in one go
One simple class can show many concepts
The instantiable class on the exam is not so bad if you figure out the data members

Here is Bus.java and BusApp.java as well which we covered in class.

Wednesday

Just as you can get overflow if numbers get to big, you can get underflow if numbers get too close to 0.
UML lets programmers visualize concepts
Methods can call themselves. If you know what you are doing you can use this to do things repeatedly
Objects can hold Objects of the same type as data members. If you know what you are doing, you can hold data conveniently.
Stack frames are diagrams that can help you track memory precisely.

We worked with the recursive Node class.

Friday

More on the Node class, which is not how we will do iteration or data
again, else-ifs are used for checking multiple conditions. They are a combination of previous syntax
if-else statements can be nested

Week 7 3/3-3/7

Monday

Instead of using else-if statements, we can use switch statements on primitive values
Use default to catch remaining cases in a switch
If you don't include break statements, the code will continue past labels, which you usually don't want.
Doing things repeatedly is a fundamental operation of computers.
The while loop takes a boolean as a condition and keeps executing as long as the boolean evaluates to true
The while loop has similar syntax to an if statement
You don't need braces, but add them anyway

Wednesday

When you wish to run a loop at least once, you may want a do-while loop
When you want to run a loop for a fixed number of times (a count controlled loop) use a for loop
You can nest loops just as you can nest if statements

Here is the (fixed) LoopExamples class with the poorly named methods. Here is the explanation of the methods.
Here's a summary of java syntax for loops, if-else statements and switch statement
Here's the chart that shows the right structure to use to get it to run a certain number of times.

Friday

Debuggers are extremely powerful tools for finding errors
Using print statements can also be quite useful for finding errors
A loop that runs until it sees a special signal is called a sentinal controlled loops
Following code through loops can be tricky and it requires some patience
Infinite loops, off-by-one errors are common. Some errors can be avoided by always including braces

Week 8: 3/10-3/14

Monday

Arrays are lists used to hold multiple related values
Arrays can't change size. They are object and must be created with new and a specific size.
You access elements of arrays by passing in an index. You can access and change elements
You can access all elements of an array with a for loop
You can make random numbers with Math.random() or the Random class

Here's the Tabloid headline generator we discussed
Here's a list of generated headlines

Wednesday

If a field and a parameter share the same name, just writing the name gives the parameter. Local varaibles also beat fields.
The extension does not affect the type of the file, but it should probably match.
Arrays must be declared and initialized like other variables.
Arrays must be created with int sizes.
Putting things in arrays you must match types.
The compiler checks types, not values. Bad indexes are runtime errors.

Here's the array error practice
Here's the array error answers

Friday

You can specify the exact values of an array if you create it in a special way
All objects can be passed to println even though there is not hundreds of methods in the PrintStream class because all objects also have type Object.
Since each object have type Object, it shares all the methods from the Object class--toString(), equals(), etc.
ArrayLists (WHICH YOU CAN'T USE IN THIS COURSE) hold many useful array functions and can hold any Object.
We are not trying to teach you the easiest way to code everything. We are trying to teach you to think like a programmer and to understand what you are writing.
If you want to put primitives (which aren't Objects) in an ArrayList or similar class (or in some other way treat them as Objects, you need a wrapper class, like Integer, Double, and Float. They are very simple classes.

Week 9: 3/24-3/28

Monday
Common array algorithms, array practice
ArrayList (CAN'T USE THESE FOR EXAMS)

Wednesday
Growing and shrinking arrays

Friday
2D arrays and higher

Week 10: 3/31-4/4
Monday
Designing classes, software life cycle, organizing classes, cohesion and coupling

Wednesday
More static, more scope, regular expressions

Friday
accessors, mutators and side effects. Pass by value vs reference

Last updated 3-12-2008