Java: Answer with explaination. Thanks

QUESTION 31

MysteryClass

-first: int -second: double;

+MysteryClass() +MysteryClass(int) +MysteryClass(double); +MysteryClass(int, double) +setData(int, double): void +getFirst(): int +getSecond(): double +doubleFirst(): int +squareSecond(): double +print(): void +equals(MysteryClass): boolean +makeCopy(MysteryClass): void +getCopy():MysteryClass

Which of the following would be a default constructor for the class MysteryClass shown in the accompanying figure?

	a.	private MysteryClass(10){ setData(); }
	b.	public MysteryClass(0, 0.0) { setData(); }
	c.	public MysteryClass(){ setData(0, 0.0); }
	d.	public MysteryClass(0) { setData(0, 0.0); }

32. Consider the following class definition. public class Rectangle { private double length; private double width; public Rectangle() { length = 0; width = 0; } public Rectangle(double l, double w) { length = l; width = w; } public void set(double l, double w) { length = l; width = w; } public void print() { System.out.println(length + " " + width); } public double area() { return length * width; } public double perimeter() { return 2 * length + 2 * width; } } Which of the following statements correctly instantiates the Rectangle object myRectangle? (i) myRectangle = new Rectangle(12.5, 6); (ii) Rectangle myRectangle = new Rectangle(12.5, 6); (iii) class Rectangle myRectangle = new Rectangle(12.5, 6);

	a.	Only (i)
	b.	Only (ii)
	c.	Only (iii)
	d.	Both (ii) and (iii)

QUESTION 36

What is the default definition of the method toString?

	a.	It creates a string that is the name of the program.
	b.	It creates a string that is the name of the package, followed by the name of the class, followed by the hash of the object.
	c.	There is no default definition; you must define the method yourself.
	d.	It creates a string that is the name of the objects class, followed by the hash code of the object.

QUESTION 39

public class Secret { private int x; private static int y; public static int count; public int z; public Secret() { x = 0; z = 1; } public Secret(int a) { x = a; } public Secret(int a, int b) { x = a; y = b; } public String toString() { return ("x = " + x + ", y = " + y + ", count = " + count); } public static void incrementY() { y++; } } Based on the class in the accompanying figure, which of the following statements is illegal?

	a.	Secret.count++;
	b.	Secret.incrementY();
	c.	Secret secret = new Secret(4);
	d.	Secret.z++;