You are probably being recorded (and transcribed) [at least if Sam can get the technology working again]
Start of class instructions
Approximate overview
If you’d like to suggest token events, please let me know in advance of class.
Like the second half of Tuesday’s lab, but extended! Also partnered. Today’s lab partner is your MP partner. If you are not here today, Sam will assign you a partner.
I will reserve ten minutes at the end of class today for you to make plans with your partner (e.g., meeting times).
For eqv. Consider the following.
XXX
XXX
There are many ways to create this.
AsciiBlock v1 = new VComp(HAlignment.LEFT, new Line("XXX"), new Line("XXX"));
AsciiBlock v2 = new VComp(HAlignment.RIGHT, new Line("XXX"), new Line("XXX"));
AsciiBlock x = new Line("X");
AsciiBlock xoverx = new VComp(x,x);
AsciiBlock v3 = new HComp(HAlignment.LEFT, xoverx, xoverx, xoverx);
AsciiBlock v4 = new Rect('X', 3, 2);
AsciiBlock v5 = new HFlip(v4);
All of the vs are equal, but none are eqv.
However, v3 would be equivalent to new HComp(HAlignment.LEFT, xoverx, new VComp(x,x), xoverx). Even though it’s built with slightly different commands, it has the same structure.
The point of the horizontal composition exercise.
Also “What should be the meaning?”
I am stunned to see how many of you wrote the following for row 0 of the surrounded box.
public String row(int i) {
if (i == 0) {
return boxChar + boxChar.repeat(contents.width()) + boxChar;
} else {
...
} // if/else
} // row(int)
Why would this disturb me? (TPS)
return boxChar.repeat(contents.width() + 2)return boxChar(width())this for clarity. this.boxChar(this.width())Will we have time limits on any LAs?
Nope. I hope that you can complete most LAs in about twenty minutes The model in most cases is that you should (a) check your notes/code/memory for something you’ve written, (b) find that thing, (c) copy/paste/edit, and (d) spend a few minutes adding narrative.
When do you plan to grade LAs?
I will try to have LAs graded by Thursday or Friday each week.
Will mini-projects always be due on Thursdays and LAs always on Mondays?
Yes.
Can I use my code from the lab in which we worked with BigFraction?
Certainly. But cite your partner.
Will we get more unit tests?
No.
Model: Read over these. Start the lab. At some point, I’ll ask if anyone has questions.
Can you give examples/situations in which one type of polymorphism is better over the other?
We tend to use parametric polymorphism when we want to build a new data type that can hold/work with “any type of object” (or perhaps some restricted types of objects). E.g., “I want a homogeneous list.”
We tend to use subtype polymorphism when we want to write methods that work with a restricted class of object. E.g., “I can do this calculation with anything that acts like a number.”
Does the letter used matter when creating a generic interface that takes multiple type parameters? In the example, T and U were used, implying that one would continue adding type parameters named V, W, X, etc., though the java.util.function.Function documentation used R and V as type parameters. Is there any correlation or importance to these?
You can use whatever letters you want. (You may even be able to use words, but no one seems to do so).
I thought Function uses
TandR.Tis used because it stands for “type”.Rstands forResult.
Is it possible to specify a type within a type specification (For example,
DynamicArray<DynamicArray<String>> to make a jagged 2D array of strings)?
Yes.
Could we dive deeper into type safety with generics and how to handle runtime exceptions related to generics?
Can you explain more about wildcard types (? super T, ? extends T) and when they are useful in practice?
How do generics in Java compare to mechanisms similar to those in other programming languages, such as C++ templates?
Could you explain this?
We assume that an object is executing each method. At times, we want to refer to that object in a method. We use the word
thisto say “the object that is executing the method”.
this.xmeans “the fieldxof the object that is executing the method.”
We see a difference if we happen to create a parameter or local variable that matches a field.
```java public class Example { int x;
void method(int x) { x = 2; // Parameter this.x; // Field } // method(int } // class Example ```
If we wanted to pass the current object to another method, we can just treat
thisas a variable.
pen.println(this).
We will stop lab at 9:35 so that you have time to discuss MP3 with your partner.
If you’ve gotten through exercise 1, 2, or 3, you can leave the remaining exercises blank.