Quiz 2 Review

Problem Q2r.1.

Define the term package as it is used in Java. Give an example of a package and its contents based on what we've used in class.

Problem Q2r.2.

What distinguishes an instance method from a static method? Give an example of each from what we've seen in class.

Problem Q2r.3.

Suppose we have the below classes and variables defined. (For example, this table indicates that Grandchild is a subclass of the Child class, and that we have defined a Grandchild variable named jacob.)

Which of the following assignment statements will the Java compiler accept?

Problem Q2r.4.

Suppose we have a class named Child, which is a subclass of another class named Parent. Each includes a constructor with no parameters. Also, Parent defines a method named scold, and Child defines a method named misbehave; both are void methods with no parameters.

Suppose we have three variables, a Child variable named kid, a Parent variable named mom, and an Object variable named x. Which of the following are legal statements?

a.	mom = new Child();
b.	kid = new Parent();
c.	x = new Child();
d.	mom.misbehave();
e.	kid.scold();

Problem Q2r.5.

Complete the below method so that it returns the number of GOvals located in the window. You'll want to use the getElement and getElementCount methods. (You should not recursively descend into GCompounds.)

public class Mystery extends GraphicsProgram {
    public void run() {
        // code adding shapes into window is not shown here
        this.println("Number of ovals created: " + countOvals());
    }

    public int countOvals() {

        int count = 0;
        for(int i = 0; i < this.getElementCount(); i++) {
            GObject obj = this.getElement(i);
            if(obj instanceof GOval) {
                count++;
            }
        }
        return count;
    }
}

Problem Q2r.6.

Problem Q2r.7.

1. What base-10 number does the eight-bit two's-complement bit pattern 01010101 represent?
2. What base-10 number does the eight-bit two's-complement bit pattern 10101010 represent?
3. Convert 26₍₁₀₎ to an eight-bit two's-complement representation.
4. Convert −104₍₁₀₎ to an eight-bit two's-complement representation.

Problem Q2r.8.

public class Problem extends Program {
    public void run() {
        double x = 3;
        double y = weird(x);
        println(x + y);
    }

    public double weird(double z) {
        println(z);
        z = z * z;
        println(z);
        return z;
    }
}

What will the program display when the run method is invoked?

3
9
12

Problem Q2r.9.

public class Problem extends Program {
    public void run() {
        double a = 3.0;
        double x = 4.0;
        weird(a);
        weird(a);
        println(x);
    }

    public void weird(double y) {
        double x = y * 2;
        y = x + 5.0;
        println(y);
    }
}

11.0
11.0
4.0

Problem Q2r.10.

What will the below program display when executed?

public class Mystery extends Program {
    public void run() {
        int a = 3;
        println(f(a));
        println(a);
    }

    public int f(int x) {
        println(g(x));
        int a = x + 5;
        println(g(a));
        return a;
    }

    public int g(int y) {
        y = y * 2;
        println(y);
        return y + 1;
    }
}

6
7
16
17
8
3

Problem Q2r.11.

What will the below program display when executed?

public class PrintLocations extends GraphicsProgram {
    public void run() {
        GRect a = new GRect(10, 10, 10, 10);
        GRect b = new GRect(40, 40, 40, 40);
        this.moveRects(a, b);
        this.println(a.getX() + " " + b.getX());
        // Note: getX returns x-coordinate of upper left corner
    }

    public void moveRects(GRect c, GRect d) {
        c = new GRect(50, 50, 50, 50);
        d.setLocation(20, 20); // moves GRect so (20,20) is upper left corner
    }
}

Problem Q2r.12.

Factorial of what? 4
4 factorial is 24

public class Problem extends Program {
    public void run() {
        int input = readInt("Factorial of what? ");
        int result = factorial(input);
        println(input + " factorial is " + result);
    }

    public int fact(int query) {

        int ret = 1;
        int cur = 1;
        while(cur <= query) {
            ret = ret * cur;
            cur = cur + 1;
        }
        return ret;
    }
}

Problem Q2r.13.

public class Problem extends Program {
    public void run() {
        double a = 16.0;
        double b = 49.0;
        println(weird(a) + "," + weird(b));
    }

    public double weird(double x) {

        if(x == 16.0) {
            return 4.0;
        } else {
            return 7.0;
        }
    }
}