Jam 3: Study Guide

Jams are open book. 40 minutes in lab.

Topics:

This quiz includes the previous topics from Jam 1-2 plus

  • functions: defining and calling, return types, return statements, parameters (aka arguments)

  • function stack, function execution

  • scope of a variable

  • arrays: defining and indexing

  • Strings: chatAt, compareTo, length

Write Java programs to check your answers. Or you can ask a TA or instructor to give feedback on your responses.

Practice questions

1) Consider the following loop

int pinLength = 4;
String pin = "";
for (int i = 0; i < pinLength; i++) {
  pin = pin + "*";
  System.out.println(pin);
}
System.out.println("Enter your pin: "+pin);

  • What is output to the console when we run this program?

  • Convert the loop above so it uses a while loop instead of a for loop

2) Write a function, Pow, that raises any number X to a power Y, using a loop. Your function should match the following specification. In your program, use main to call and test your function.

// Function: Pow
// Description: Computes X to the power Y
// Input X (double), the number to raise to a power
// Input Y (double), the exponent
// Returns (double), the quantity X^Y

3) Write a function, Average, that takes an array of doubles as input and returns the average value based on the specification below. In your program, use main to call and test your function using random values in the range [-5, 5).

// Function: Average
// Description: Computes the average value in a list of numbers
// Input data (double[]), the numbers to average
// Returns (double), the average value, or 0 if the size of data is 0

public static void main(String[] args)
{
  double[] values = new double[5];
  // todo - initialize values with random values in range [-5,5)
  // todo - call average and print the result
}

4) Write a function, CountLetter, which counts the number of times a character occurs in a String. Implement tests in main to check your function. For example,

  • CountLetter("elephant",'e') should return 2.

  • CountLetter("zebra", 'z') should return 1.

  • CountLetter("elephant", 'z') should return 0.

5) Write a function, IsEvenLength, which returns true if the given String has an even number of characters and false otherwise. Implement tests in main to check your answer. For example,

  • IsEvenLength("cat") returns false

  • IsEvenLength("") returns true

  • IsEvenLength("a") returns false

6) Consider the following program

class Mystery {
  public static String mystery2(String message, String symbol) {
    message = symbol+message+symbol;
    // (a) Show function stack here
    return message;
  }

  public static void mystery1(String message) {
    System.out.println(message);
    message = mystery2(message, "~~");
    System.out.println(message);
    // (b) Show function stack here
  }

  public static void main(String[] args) {
    String userText = "Happy Halloween!";
    mystery1(userText);
    System.out.println(userText);
  }
}

  • On the line labeled (a), what functions are in the function stack? List the contents of the stack with the oldest contents at the top, same as on Java tutor

  • On the line labeled (b), what functions are in the function stack?

  • What local variables are defined in mystery2?

  • What local variables are defined in mystery1?

  • What parameters are defined in mystery1?

  • What is the return type of mystery1?

  • What is the return type of mystery2?

  • What variables are in scope in main?

  • What variables are in scope in mystery1?

  • What variables are in scope in mystery2?

  • What is the console output of this program?

7) Implement a Movie class. Movie should contain the following data and methods

// Data

// Title (string)
// Duration in minutes (float)
// Year (integer)
// actors (array of String)

// Methods

// Constructor
// Input: Title (string)
// Input: Duration in minutes (float)
// Input: Year (integer)
// Input: actors (array of String)

// Accessor for title
// Mutator for title

Test your Movie class. Create a Movie object for "The Shining" which was made in 1980, is 2 hours and 26 minutes long, and stars Jack Nicholson and Shelley Duval. Create your object in setup()