Download CSCI 1302 Guided Notes: Chapter 9 – Object Referencing Dr

CSCI 1302 Guided Notes: Chapter 9 – Object Referencing
Dr. Phelps
Passing Objects As Arguments to Methods (Section 9.2)
5. Examine the program that passes a primitive value, num to a method. What happens if you change the value of the
num in the method?
public static void main (String [] args)
{
int num = 5;
System.out.println( num); // Display the num’s value.
changeInteger(num);
// Pass the number to the changeInteger method.
System.out.println( num); // Display the object's contents again.
}
public static void changeInteger(int x)
{ x = 0;
}
6. Examine the program that creates an instance of the Rectangle class and then passes a reference to that object as an
argument to a method. What happens if you change the value of the rectangle in the method?
public static void main(String[] args)
{ Rectangle box = new Rectangle(12, 5);
// Display the object's contents.
System.out.println( box.getHeight()+ " X " + box.getWidth());
// Pass a reference to the object to the changeRectangle method.
changeRectangle(box);
// Display the object's contents again.
System.out.println( box.getHeight()+ " X " + box.getWidth());
}
public static void changeRectangle(Rectangle r)
{ r.setHeight(0);
r.setWidth(0);
}
Writing an equals method: (9.5)
7. Examine the program that compares two integers and two rectangles. What is the output?
{
public class Compare
public static void main(String []args)
{ int num1;
int num2;
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter a number: ");
num1 = keyboard.nextInt();
System.out.print("Enter another number: ");
num2 = keyboard.nextInt();
Rectangle rectA = new Rectangle(num1, num2);
Rectangle rectB = new Rectangle(num1, num2);
if (num1 == num2)
System.out.println("The numbers are equal");
else
System.out.println("The numbers are NOT equal");
if (rectA == rectB)
System.out.println("The rectangles are equal");
else
System.out.println("The rectangles are NOT equal");
}
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CSCI 1302 Guided Notes: Chapter 9 – Object Referencing
Dr. Phelps
8. Write an equals method in the Rectangle class that could be used to compare two rectangle objects and returns true
if the corresponding instance fields are the same. Write a call statement to compare two rectangles using the equals
method.
9. Even if you do not write an equals method for a class, Java provides one. Describe the behavior of the equals
method that java automatically provides.
The toString Method (9.4)
10. Define a toString method in the Rectangle class that will return a String with the height and width of a rectangle
formatted as: 2 X 4. Write a corresponding call statement using the toString method.
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