W1: OOP

Please submit your answers to the questions as comments in a W1.txt file you’ll be writing in this lecture.

Grading rubric and submission

When you are done, submit your W1.txt file to BB.

You will be graded on the following:

Item Points
Answers are correct 100

Questions

1

Which of the following is a reference type and which is a primitive type?

int a;
double b;
int c[] = {1, 2, 3};
String s = "Hello World";

2

Four part question:

  1. What is a static method in Java?

  2. Why does the main method need to be a static method?

public class Hello {
    public static void main(String[] args) {
        System.out.println("hello, world");
    }
}

  1. What is a static field in java?

  2. What is the relationship between static fields and static methods, versus non-static fields and non-static methods?

3

What is the output of the following programs?

/* Program 1 */
public static void main(final String args[]) {
    String choice = new String("A");
    if (choice == "A") {
        System.out.println("Correct");
    }
    else {
        System.out.println("Wrong");
    }
}
/* Program 2 */
public static void main(final String args[]) {
    String choice = new String("A");
    if (choice.equals("A")) {
        System.out.println("Correct");
    }
    else {
        System.out.println("Wrong");
    }
}

4

Does the below program change the season? Why, or why not?

static void change_season(String str) {
    str = "Spring";
}

public static void main(final String args[]) {
    String season = "Winter";
    change_season(season);
    System.out.println("The current season is: " + season);
}

5

What is the this keyword in Java?

6

What is the output of the main method below? Please explain.

public class Point {
    double x = 0;
    double y = 0;

    public Point(double x, double y) {
        x = x;
        y = y;
    }
}
public static void main(final String args[]) {
    Point point = new Point(1, 2);
    System.out.println("X: " + point.x + " Y: " + point.y);
}

7

In the Point class below, how does Java choose between the two constructors?

public class Point {

   private double x, y; 
   
   public Point(double x, double y) {
        this.x = x;
        this.y = y;
   }

   public Point(Point other) {
       this.x = other.getX();
       this.y = other.getY();
   }

}