5.12. Mixed Up Code Practice

Try to solve each of the following. Click the Check Me button to check each solution. You will be told if your solution is too short, has a block in the wrong order, or you are using the wrong block. Some of the problems have an extra block or two that aren’t needed in the correct solution. Try to solve these on your phone or other mobile device!

The following program segment should define a Dog class with a constructor that takes one parameter, name, and sets the value of the Dog’s private name attribute to that. There should also be a getName method which returns the name attribute of the Dog object. But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Dog
{
---
  private String name;
---
  public String name; #paired: Instance variables should be encapsulated
---
  public Dog(String name)
  {
---
  public Dog Dog(String name)
  { #paired: Constructors never have a return type
---
    this.name = name;
---
  } // end constructor

  public String getName()
  {
---
    return this.name;
---
  } // end getName
} //end class
        

The following program segment should define a Dog class with a constructor that takes two parameters: name (a String) and age (an integer). These parameters should be saved in correspondingly-named private instance variables. But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Dog
{
---
public class Dog #paired: Curly braces are required when declaring a class
---
  private String name;
  private int age;
---
  public Dog(String name, int age)
  {
---
  public Dog(name, age)
  { #paired: Methods need to specify the types for arguments
---
    this.name = name;
    this.age = age;
---
    name = name;
    age = age; #paired: When the parameter name is the same as an attribute, you MUST use "this" to refer to the attribute
---
  } // end constructor
} // end class
        

The following program segment should define a Cat class with a constructor that takes two parameters: name (a String) and age (an integer). These parameters should be saved in correspondingly-named private attributes of Cat objects. Next, there should be a makeSound method that prints "meow". Finally, there should be a toString method that returns “Name: name, Age: age” (such that Cat("Lucky", 10)’s toString method would return “Name: Lucky, Age: 10”). But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Cat
{
---
  private String name;
  private int age;

  public Cat(String name, int age)
  {
---
    this.name = name;
    this.age = age;
---
  } // end constructor

  public void makeSound()
  {
---
  } // end constructor

  public String makeSound()
  { #paired: When a method returns nothing, its return type should be "void"
---
     System.out.println("meow");
---
  } // end makeSound

  public String toString()
  {
---
    return "Name: " + this.name + ", Age: " + this.age;
---
  } // end toString
} //end class
        

The following program segment should define a Square class with a constructor that takes one parameter: length (an integer). This parameter should be saved in a correspondingly-named private attribute of Square objects. The Square class should also have a variable numberOfSquares that tracks how many squares have been created. Finally, there should be a toString method which returns "Length: length" (such that Square(10)’s toString method would return "Length: 10". But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Square
{
---
  public static int numberOfSquares = 0;
  private int length;
---
  private int numberOfSquares = 0;
  private int length; #paired: When you need a variable to be accessible for every object of a class, it should be static
---
  public Square(int length)
  {
---
    this.length = length;
    numberOfSquares++;
---
  } // end constructor
---
  public String toString()
  {
---
    return "Length: " + this.length;
---
  } // end toString
} //end class
        

The following program segment should define a Rectangle class with a constructor that can take zero or two integer parameters. With zero arguments passed, the Rectangle should be initialized with a length of 10 and a width of 10. With two integers passed, the Rectangle should have a length equal to argument1 and a width equal to argument2. There should also be an getArea method that returns the area length times width. But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Rectangle
{
---
  private int length;
  private int width;

  public Rectangle()
  {
---
    this.length = 10;
    this.width = 10;
---
  } // end zero-argument constructor

  public Rectangle(int length, int width)
  {
---
    this.length = length;
    this.width = width;
---
  } // end two-argument constructor

  public int getArea()
  {
---
    return this.length * this.width;
---
  } // end getArea
} // end class
        

The following program should define a CelestialBody class. The class should have two instance variables: orbitLength and daysSinceDiscovered. The orbitLength variable should be initialized through the constructor, while daysSinceDiscovered should be derived from orbitLength and the orbit method. The orbit(int numberOfTimes) should add orbitLength * numberOfTimes to daysSinceDiscovered (e.g., if Planet X has done two orbits with an orbit length of 12 days, it was discovered 24 days ago. If it then orbits another three times, it was discovered 60 days ago). But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class CelestialBody
{
---
  private int orbitLength;
  private int daysSinceDiscovered;
---
  public CelestialBody(int orbitLength)
  {
---
    this.daysSinceDiscovered = 0;
    this.orbitLength = orbitLength;
---
    this.orbitLength = orbitLength; #paired: daysSinceDiscovered needs to be initialized
---
  } // end constructor

  public void orbit(int numberOfTimes)
  {
---
  } // end constructor

  public int orbit(int numberOfTimes)
  { #paired: A method who returns nothing should have a void return type
---
    this.daysSinceDiscovered += this.orbitLength * numberOfTimes;
---
  } // end orbit
} // end class
        

The following program should define a Person class. Each Person instance should have a String name attribute and a integer age attribute. There should also be getName and setName functions. But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Person
{
---
  private String name;
  private int age;

  public Person(String name, int age)
  {
---
    this.name = name;
    this.age = age;
---
  } // end constructor

  public String getName()
  {
---
    return this.name;
---
  } // end getName

  public void setName(String newName)
  {
---
    this.name = newName;
---
  } // end setName
} // end class
        

The following program should define a Point class. Each Point instance should have integer x and y attributes (there are associated getX and getY methods whose implementations aren’t shown). There should be a getDistance method that takes in another Point object as an argument and calculates the distance from this object to that one (which would be sqrt((this.x - other.x) ^ 2 + (this.y - other.y) ^ 2)). But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Point
{
---
  private int x;
  private int y;

  public Point(int x, int y)
  {
---
    this.x = x;
    this.y = y;
---
  } // end constructor

  public double getDistance(Point other)
  {
---
    return Math.sqrt(Math.pow(this.x - other.getX(), 2) + Math.pow(this.y - other.getY(), 2));
---
    return Math.sqrt((this.x - other.getX()) ** 2 + (this.y - other.getY()) ** 2); #paired: Exponents in java should use Math.pow
---
  } // end getDistance
} // end class
        

The following program should define an Account class. Each Account instance should have integer balance and String owner attributes (and the constructor should take those in that order). To decrease balance, there should be a withdraw method that takes in an integer argument and subtracts that from balance. However, if balance would end as a negative number, it should just be set to zero. But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Account
{
---
  private int balance;
  private String owner;

  public Account(int balance, String owner)
  {
---
    this.balance = balance;
    this.owner = owner;
---
  } // end constructor

  public void withdraw(int amount)
  {
---
    if (amount > this.balance)
    {
---
      this.balance = 0;
---
    } // end if

    else {
---
      this.balance -= amount;
---
    } // end else
---
  } // end withdraw
} // end class
        

The following program should define a Character class. Each Character instance should have a integer healthPoints attribute and a String name attribute. There is a constructor and getHP, setHP, and getName methods that are not shown. Finally, there needs to be a fight(Character other) method that lets a character fight another. If the character’s healthPoints are the same or more than other’s, other’s HP should be set to zero, the current character’s HP should be set to the difference, and the program should print “{the character’s name} wins”. If other’s HP is greater, the current character’s HP should be set to zero, other’s HP should be set to the difference, and the program should print “{other’s name} wins”. But the blocks have been mixed up and include pairs of lines where one is unneeded. Drag the necessary code from the left to the right and put them in order so that the code would work correctly. Click the Check button to check your solution.

        public class Character
{
---
  // instance variables, constructor, & getter/setters not shown
---
  public void fight(Character other)
  {
---
    if (this.getHP() >= other.getHP())
    {
---
    this.setHP(this.getHP() - other.getHP());
    other.setHP(0);
    System.out.println(this.getName() + " wins");
---
    } // end if
---
    else
    {
---
      other.setHP(other.getHP() - this.getHP());
      this.setHP(0);
      System.out.println(other.getName() + " wins");
---
    } // end else
---
  } // end fight
} // end class
        

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