Review for Quiz 2

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Generics

Question 2-1

Name and explain a reason why generics (such as generic packages in Ada or templates in C++) are a useful feature for a programming language to include.

Solution

Object-oriented features

Question 2-2

Write the withdraw: method of our Account class so that the balance cannot drop below 0.

Solution

Question 2-3

Say you want to add a unary instance method into Smalltalk's built-in Integer class called abs, which returns the absolute value of the Integer instance to which the method is applied. Write the definition of this method.

Solution

Question 2-4

Name two significant and distinct differences between the object-oriented features of Java and Smalltalk. Do not address other differences, like their radically different syntax.

Solution

Question 2-5

Consider the following Java program.

class A {
    int f() { return 1; }
}

class B extends A {
    int f() { return 0; }
}

class Main {
    public static void main(String[] args) {
        A a = new B();
        System.out.println(a.f());
    }
}

What does this program print?

Solution

Question 2-6

Consider the following program.

class Ident {
    int f(int x) { return x; }
    int g(int x) { return f(f(x)); }
}

class Square extends Ident {
    int f(int x) { return x * x; }
}

class Main {
    public static void main(String[] args) {
        Ident a = new Ident();
        Ident b = new Square();
        Square c = new Square();
        System.out.println(a.g(3) + " " + b.g(3) + " " + c.g(3));
    }
}

What does this program print?

Solution

UML and patterns

Question 2-7

Draw the Listener pattern using an UML Class Diagram.

Solution