Practice Questions (Code Writing)

Making Decisions (Conditionals)

Table of contents

Easy Level Code Writing Questions
Easy CodeCheck Questions
Medium Level Code Writing Questions
Medium CodeCheck Questions
Hard Level Code Writing Questions

Easy Level Code Writing Questions

We want to add a button to the tally counter given below that allows an operator to undo an accidental button click. Provide a method
public void undo()
that simulates such a button. As an added precaution, make sure that clicking the undo button more often than the click button has no effect. (Hint: The call Math.max(n, 0) returns n if n is greater than zero, zero otherwise.)

/**
   This class models a tally counter.
*/
public class Counter
{
   private int value;
   /**
      Gets the current value of this counter. 
      @return the current value
   */
   public int getValue()
   {
      return value;
   }
   /**
      Advances the value of this counter by 1
   */
   public void click()
   {
      value = value + 1;
   }
   /**
      Resets the value of this counter to 0
   */
   public void reset()
   {
      value = 0;
   }
}

Simulate a tally counter that can be used to admit a limited number of people. First, the limit is set with a call
public void setLimit(int maximum)
If the click button is clicked more often than the limit, it has no effect. (Hint: The call Math.min(n, limit) returns n if n is less than limit, and limit otherwise.)
Write a class RangeInput that allows users to enter a value within a range of values that is provided in the constructor. An example would be a temperature control switch in a car that allows inputs between 60 and 80 degrees Fahrenheit. The input control has “up” and “down” buttons. Provide up and down methods to change the current value. The initial value is the midpoint between the limits. As with the preceding exercises, use Math.min and Math.max to limit the value. Write a sample program that simulates clicks on controls for the passenger and driver seats.
Simulate a circuit for controlling a hallway light that has switches at both ends of the hallway. Each switch can be up or down, and the light can be on or off. Toggling either switch turns the lamp on or off. Provide methods
```
public int getFirstSwitchState() // 0 for down, 1 for up public int getSecondSwitchState()
public int getLampState() // 0 for off, 1 for on public void toggleFirstSwitch()
public void toggleSecondSwitch()
```
(TEST) Write a CircuitTester class that tests all switch combinations, printing out actual and expected states for the switches and lamps.
Change the method headers of the circuit class so that it has the following methods:
```
public int getSwitchState(int switchNum)
public int getLampState()
public void toggleSwitch(int switchNum)  
```
Provide an implementation using only language features that have been introduced. The challenge is to find a data representation from which to recover the switch states.
Write a program that displays the properties of a letter-size (8.5 × 11 inches) sheet of paper in millimeters. There are 25.4 millimeters per inch. The program should print:
• The width and height
• The perimeter
• The length of the diagonal
Use constants and comments in your program.
Write a program that reads a number and displays the square, cube, and fourth power. Use the Math.pow method only for the fourth power.
Write a program that prompts the user for two integers and then prints
• The sum
• The difference
• The product
• The average
• The distance (absolute value of the difference)
• The maximum (the larger of the two)
• The minimum (the smaller of the two)
Hint: The max and min functions are declared in the Math class.

Easy CodeCheck Questions

Complete the program below so that it prompts for and reads in two integer values, and then prints out the larger of the two. Solve it here
Complete the program below so that it prompts for and reads in three integer values, and then prints out the smallest of the three.
For example, one sample run of this program looks like the following:
Please enter three integer values: 66 22 34
Smallest: 22
Solve it here
Complete the program below so that it prompts for and reads in a student’s final class average (0.0 to 100.0), and prints out the letter grade the student should receive, based on the following table:
A : greater than 90.0, up to 100.0
B : greater than 80.0, up to 90.0
C : greater than 70.0, up to 80.0
D : greater than 60.0, up to 70.0
F : 0.0 up to 60.0
For example, if a student’s final class average is 84.6, he has earned a letter grade of B.
Solve it here
Employees get paid “time and a half” for the weekly work hours in excess of 40 hours. For example, an employee making $10/hour and working 50 hours in a given week gets paid $10 for the first 40 hours and $15 for the remaining 10 hours, for a total weekly pay of $550.

Solve it here
Complete the getMiddle method that gets the middle character from a word if the word length is odd, or the middle character pair if it is even. For example, getMiddle(“Java”) returns “av”. If the word is empty, return the empty string. If it is null, return null.

Solve it here
Write a method to test whether four numbers are all the same. For example,

3, 3, 3, and 3 are all the same 3, 3, 4, 3 are not all the same 3, 4, 5, 5 are not all the same

Solve it here
Write a method to test whether three numbers are all different. For example,

3, 5, and 4 are all different 3, 3, 4 are not all different 3, 3, 3 are not all different

Solve it here
Write a method to test whether three numbers have the same sign (positive, zero, or negative). For example,

-3, -4, -5 have the same sign 3, 4, -5 do not have the same sign 3, 4, 0 do not have the same sign (because 0 is not positive) 0, 0, 0 have the same sign

Solve it here

Medium Level Code Writing Questions

Suppose you want to implement a class TimeDepositAccount. A time deposit account has a fixed interest rate that should be set in the constructor, together with the initial balance. Provide a method to get the current balance. Provide a method to add the earned interest to the account. This method should have no arguments because the interest rate is already known. It should have no return value because you already provided a method for obtaining the current balance. It is not possible to deposit additional funds into this account. Provide a withdraw method that removes the entire balance. Partial withdrawals are not allowed.
(TEST) Write a BankAccountTester class whose main method constructs a bank account, deposits 1,000, withdraws 500, withdraws another 400, and then prints the remaining balance. Also print the expected result.

Refer to the BankAccount class here
Add a method
public void addInterest(double rate)
to the BankAccount class that adds interest at the given rate. For example, after the statements
```
BankAccount momsSavings = new BankAccount(1000); 
momsSavings.addInterest(10); // 10 percent interest
```
the balance in momsSavings is 1,100. Also supply a BankAccountTester class that prints the actual and expected balance.
Write a class SavingsAccount that is similar to the BankAccount class, except that it has an added instance variable interest. Supply a constructor that sets both the initial balance and the interest rate. Supply a method addInterest (with no explicit parameter) that adds interest to the account. Write a SavingsAccountTester class that constructs a savings account with an initial balance of 1,000 and an interest rate of 10 percent. Then apply the addInterest method and print the resulting balance. Also compute the expected result by hand and print it.

Consider the following class, CashRegister:

/**
   A cash register totals up sales and computes change due.
*/
public class CashRegister {
   private double purchase; 
   private double payment;
   /**
      Constructs a cash register with no money in it.
   */ 
   public CashRegister() {

   }
   /**
      Records the sale of an item. 
      @param amount the price of the item
   */ 
   public void recordPurchase(double amount) {
      purchase = purchase + amount;
   }
   /**
      Processes a payment received from the customer. 
      @param amount the amount of the payment
   */ 
   public void receivePayment(double amount) {
      payment = payment + amount;
   }
   /**
      Computes the change due and resets the machine for the next customer. 
      @return the change due to the customer
   */
   public double giveChange() {
      double change = payment - purchase; 
      purchase = 0;
      payment = 0; 
      return change;
   }
}

Add a method printReceipt to the CashRegister class. The method should print the prices of all purchased items and the total amount due. Hint: You will need to form a string of all prices. Use the concat method of the String class to add additional items to that string. To turn a price into a string, use the call String.valueOf(price).

After closing time, the store manager would like to know how much business was transacted during the day. Modify the CashRegister class to enable this functionality. Supply methods getSalesTotal and getSalesCount to get the total amount of all sales and the number of sales. Supply a method reset that resets any counters and totals so that the next day’s sales start from zero.
Implement a class Employee. An employee has a name (a string) and a salary (a double). Provide a constructor with two arguments
public Employee(String employeeName, double currentSalary)
and methods
public String getName()
public double getSalary()
public void raiseSalary(double byPercent)
These methods return the name and salary, and raise the employee’s salary by a certain percentage. Sample usage:
Employee harry = new Employee("Hacker, Harry", 50000);
harry.raiseSalary(10); // Harry gets a 10 percent raise
Supply an EmployeeTester class that tests all methods.
Implement a class Product. A product has a name and a price, for example new Product("Toaster", 29.95). Supply methods getName, getPrice, and reducePrice. Supply a program ProductPrinter that makes two products, prints each name and price, reduces their prices by 5.00, and then prints the prices again.

What does the following method do? Give an example of how you can call the method.

public class BankAccount {
   public void mystery(BankAccount that, double amount) {
      this.balance = this.balance - amount; 
      that.balance = that.balance + amount;
   }
   . . . // other BankAccount methods
}

Answer

BankAccount account1 = new BankAccount();
BankAccount account2 = new BankAccount();
account1.mystery(account2, 2000);

Medium CodeCheck Questions

Complete the program below so that it prompts the user for a temperature value, followed by a character that represents the type of temperature:
- C for Celsius
- F for Farhenheit
If the character represents Fahrenheit temperature (F), convert the temperature value to the equivalent value in Celsius, using the following formula:
C = (5/9)(F - 32.0)
where C represents the Celsius temperature value, and F represents the Farhenheit temperature value.
If the character represents Celsius temperature (C), convert the temperature value to the equivalent value in Farhenheit, using the following formula:
F = (9/5)C + 32.0
with F and C defined the same as above.
Print the converted value.
Solve it here
Consider a program that administers multiple-choice quizzes. The student needs to provide a response such as A or D. Your job will be to check for input errors in the student response string. Check that the string has length 1, and that it is a letter between A and the last valid choice for the problem. Solve it here
An open interval is the set of all numbers between a lower and upper bound. In mathematical notation, we write

(a, b) = { x | a < x < b }

Your task is to determine when two intervals overlap. For example, the intervals (1, 3) and (2, 4) overlap, as do (1, 4) and (2, 3). But the intervals (1, 2) and (3, 4) do not overlap.

Solve it here
A simple guessing game asks the player to guess a number between 1 and 50. Hints are returned depending on how far from the number the guess is.

20 or more above the number: The hint is “Burning Hot” 10 to 19 above the number: The hint is “Hot” 5 to 9 above the number: The hint is “Warm” 4 below the number to 4 above: The hint is “Pleasant” 5 to 9 below the number: The hint is “Cool” 10 to 19 below the number: The hint is “Cold” 20 or more below the number: The hint is “Ice Cold”

Solve it here