CS 199 EMP

Hosted by Jackie Chan and Akhila Ashokan

Topics: Function Overloading, Void Return, Strings

Today's Learning Objectives

Review and practice:

  • Function Overloading
  • Void Returns
  • Strings

Write code on the homepage or any playground on the site!
https://cs125.cs.illinois.edu/

Slides are on the course site!
https://cs199emp.netlify.app/

How to follow along

  • Small breakout rooms of working together

  • Work for 10-15 minutes together, feel free to use paper, whiteboards, online share tools.

  • Use the Jeed playground on the 125 homepage for the interactive running

Function Overloading

Function overloading is when you make different functions with the same name.

  • This is to deal with different types of and number of inputs

  • Different data types may be processed differently

int area(int l, int h) {
  return l * h;
}

float add(float l, float h) {
  return l * h
}

Function Overloading

We distinguish functions via their signatures for overloading.

  • Signature = name + inputs(names, type, order)

  • area(int, int), area(float, float)

  • Note that having the return type different doesn't change the signatures. float area(int l, int h) and int area(int l, int h) are the same function as far as overloading is concerned.

  • Having the same type, order, and number but different name does not work either. area(int a, int b) and area(int l, int h) are the same function as far as overloading is concerned.

Function Overloading - Practice

Write two overloaded functions area to calculate the area of a circle and triangle

  • double area(double radius) - πr2\pi r^2. Feel free to use π=3.14159\pi = 3.14159

  • double area(double base, double height) - 12bh\frac{1}{2}bh

Function Overloading - Starter code (5 mins)

double area(double radius) {
  return 0.0; // implement
}

double area(double base, double height) {
  return 0.0; // implement
}

Void Returns

Void returns happen only when a fucntions DOESN'T return a value. This changes the declaration of the function to a void return type.

void <functionName>(<data type> <argumentName>) {
    <code>;
}

void sayMyName(String myName) {
  System.out.println("Hi there, " + myName);
}

sayMyName("Jarvis"); // this works
System.out.println(sayMyName("Jarvis")); // will this work? why or why not?
String myName = sayMyName("Jarvis"); // why does this fail?

Can you think of a function where you would use the void return type?

Void Returns - Practice (5 mins)

Create a function that will print out statements based on two parameters passed into the function: likeEMP and likeCoding. If you like both, it should print out "Yay, we're so glad you like this class." If you liked one or the other, print out "Aww, which one didn't you like?" If you liked neither, print out "Dang, what can we do better?" (Hint: you should be using a void return type)

Void Returns - Practice (5 mins)

Can you have a return statement in a function that has a return type of void? In other words, does the function below work?

void isNumTwo(int num) {
  if (num == 2) {
    System.out.println("Yes, this number is two.");
  }
  return;

  // What happens if I write a print statement here?
}

Strings

  • Strings are the Java data type for working with text/a sequence of characters.

  • This is our first example of an object data type in Java. Java objects combine together state and behavior.

  • Strings are different from chars because they are enclosed in double quotes ("")

String welcome = "Welcome to the world of Strings! "; 
String soMuch = "There is so much we can do with Strings. ";
String emojiis = "We can even use emojiis now! 🙌";
System.out.println(welcome + soMuch + emojiis);

More fun with Strings

  • Concatenation
String question = "Can you call, ";
String name = "Ms.Potts?";
System.out.println(question + name);
  • Dot notation
String full = "Can you call, Ms.Potts?";
System.out.println(full.length()); 
// how this this different from the way we find the length of an array?
  • The new operator - where have we seen this before?
String opinion = "My favorite Marvel super hero is Iron Man.";
String opinionTwo = new String("My favorite Marvel super hero is Captain America.");

Even more fun with Strings

  • The split method
String opinion = "My favorite Marvel super hero is Iron Man.";
String[] arr = opinion.split(" ");
System.out.println(arr[2]); // What does this print out?
  • The substring method
String opinionTwo = new String("My favorite Marvel super hero is Captain America.");
String sub = opinionTwo.substring(33);
// Substring can also take two arguments: beginIndex and endIndex.
// A real example of function overloading!
System.out.println(sub);

Strings - Practice (5 mins)

Create a function called combineStrings that will output a new String in the form short+long+short where short is the shorter of the two strings and long is the longer of the two strings. The two strings will not be of the same length.

String combineStrings(String a, String b) {
  // write your code here 
}

For example String a = "Dog" and String b = "Fish" should return "DogFishDog".

Strings - Practice (5 mins)

Given a string, return a string length 1 from its front, unless front is false, in which case return a string length 1 from its back. The string will be non-empty.

theEnd("Hello", true) → "H"
theEnd("Hello", false) → "o"
theEnd("oh", true) → "o"

String theEnd(String str, boolean front) {
    // write your code here 
}

Final Questions? You're Doing Awesome.

boolean empStudent = true;

if (empStudent) {
    System.out.println("You're awesome, and you'll do awesome in the course!");
}

Give us feedback!
What did you guys think? Are the questions too hard? Too easy? Let us know in the feedback form available on the course site.
https://cs199emp.netlify.app/

Solutions Section (Spoiler Alert!)

Function Overloading - Practice

double area(double radius) {
  return 3.14159 * radius * radius;
}

double area(double base, double height) {
  return base * height / 2.0;
}

Void Returns - Practice

void likeEmpAndCoding(boolean likeEMP, boolean likeCoding) {
  if (likeEMP && likeCoding) {
    System.out.println("Yay, we're so glad you like this class");
  } else if (likeEMP || likeCoding) {
    System.out.println("Aww, which one didn't you like?");
  } else { 
    System.out.println("Dang, what can we do better?");
  }
}

likeEmpAndCoding(true, true); // try calling this method with different inputs

Void Returns - Practice

Can you have a return statement in a function that returns void? Yes, void functions can still return so this code will run fine. The return will just exit the function, but it will not actually return anything.

void isNumTwo(int num) {
  if (num == 2) {
    System.out.println("Yes, this number is two.");
  }
  return;
}

Strings - Practice

public String comboString(String a, String b) {
  if (a.length() > b.length()) {
    return b + a + b;
  } else {
    return a + b + a;
  }
}

Strings - Practice

public String theEnd(String str, boolean front) {
  if (front) {
    // Get the first letter.
    return str.substring(0, 1);
  } else {
    // Get the last letter.
    return str.substring(str.length() - 1, str.length());
  }
}