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152 lines
3.8 KiB
Markdown
152 lines
3.8 KiB
Markdown
---
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title: "Recitation 11: Exam 2 Review"
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date: 2022-04-04T15:40:12-04:00
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draft: false
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tags: []
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math: false
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---
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## Conceptual Questions
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1. When must a representation invariant hold?
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2. What's the difference between a representation invariant and an abstract function?
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3. Which type of testing only considers the specifications and not the implementation?
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4. What is the difference between overriding and overloading a method?
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5. Provide an example of representation exposure.
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6. Are Java subtypes true subtypes? Why or why not?
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## Overloading vs Overriding: Spaghetti Code Edition
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Consider the following Java code
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```java
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class A {
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void m(A a) { System.out.println("AA"); }
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void m(B a) { System.out.println("AB"); }
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void m(C a) { System.out.println("AC"); }
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}
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class B extends A {
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void m(A a) { System.out.println("BA"); }
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void m(B a) { System.out.println("BB"); }
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void m(C a) { System.out.println("BC"); }
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}
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class C extends B {
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void m(A a) { System.out.println("CA"); }
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void m(B a) { System.out.println("CB"); }
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void m(C a) { System.out.println("CC"); }
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}
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A a1 = new A();
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A a2 = new B();
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A a3 = new C();
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B b1 = new B();
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B b2 = new C();
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C c1 = new C();
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```
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1. Fill in the following table with the output of `row.m(col)`
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| | a1 | a2 | a3 | b1 | b2 | c1 |
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|--- |--- |--- |--- |--- |--- |--- |
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| **a1** | | | | | | |
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| **a2** | | | | | | |
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| **a3** | | | | | | |
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| **b1** | | | | | | |
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| **b2** | | | | | | |
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| **c1** | | | | | | |
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2. How would the grid change if I print it like below?
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```java
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A[] all = {a1, a2, a3, b1, b2, c1};
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for (A some_a : all) {
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for (A some_a2 : all) {
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some_a.m(some_a2); System.out.print(" ");
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}
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System.out.println("");
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}
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```
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| | a1 | a2 | a3 | b1 | b2 | c1 |
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|--- |--- |--- |--- |--- |--- |--- |
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| **a1** | | | | | | |
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| **a2** | | | | | | |
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| **a3** | | | | | | |
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| **b1** | | | | | | |
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| **b2** | | | | | | |
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| **c1** | | | | | | |
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## Generics and Advanced Typing
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Consider the following Java code:
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```java
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class Mammal {}
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class Cow extends Mammal {}
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class Horse extends Mammal {}
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class ToyHorse extends Horse {}
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Mammal m = new Mammal();
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Object o = new Object();
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Horse h = new Horse();
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ToyHorse t = new ToyHorse();
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List<? extends Mammal> lem = new ArrayList<>();
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List<? extends Horse> leh = new ArrayList<>();
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List<? super Horse> lsh = new ArrayList<>();
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```
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For each of the following, note whether or not it will compile.
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1. `lem.add(h);`
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2. `lsh.add(t);`
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3. `lsh.add(o);`
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4. `lem.add(null);`
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Assume that the ArrayList have elements in them.
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5. `h = lsh.get(0);`
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6. `m = leh.get(0);`
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7. `o = lsh.get(0);`
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## Equivalence Relations
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1. What are the three properties that you need to show in order to prove that the method is an equivalence relation.
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2. Is the following an equivalence relation? If so, prove. Otherwise provide counterexample.
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```java
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class String {
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public boolean equals(String other) {
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for (int i = 0; i < this.length; i++) {
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if (this.contents[i] != other.contents[i]) {
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return false;
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}
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}
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return true;
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}
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}
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```
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3. Is the following an equivalence relation? If so, prove. Otherwise provide counterexample.
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```java
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class FuzzyNumber {
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public boolean equals(FuzzyNumber other) {
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// Check: this - 0.5 <= other <= this + 0.5
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return this.number - 0.5 <= other.number && other.number <= this.number + 0.5;
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}
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}
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```
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4. Is the following an equivalence relation? If so, prove. Otherwise provide a counterexample.
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```java
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class FuzzyNumberEnhanced {
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public boolean equals(FuzzyNumberEnhanced other) {
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return this.number - other.number == 0
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}
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}
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```
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