Functions

1. Open and run Functions.java.

• What do you notice about the code?
• What do you notice about the result?

2. Break down what you see.

  This tells Java that we want a *function* in our class
  |     This tells Java we won't return anything
  |     |    This is what we name our function
  |     |    |     These parentheses include paramaters. (none)   
  v     v    v     v
static void printHi(){
   // This is the code we are running
   System.out.println("Hello!");
}

• This breakdown uses unknown language like class, and paramaters, which we will learn later.

3. Edit the code in the function.

• Add some other println to the function. Remember, the code should be put in after the first println, but before the ending curly bracet (}).
• Run the code, and see what happens.

4. Functions make code easier to write and read.

• Think back on the MathProblems.java you wrote. How could you improve this with functions?
• You will need to learn one more thing about functions before you can rewrite MathProblems with functions.

Parameters

1. Open Parameters.java, and run it.

• What is different about the calls (the function name with parentheses) in main?
• Change some of the numbers in the parentheses of the calls.
• Look through the square(int num) function. What do you think it does?

2. Change the square function into a multiply function.

• While this may seem redundant (Why not just use *?), it is easy for practice.
• Add another parameter into the square function, by adding a comma, and then another variable declaration.

Click for solution.

static void square(int num, int num2)

• Rename the function by right-clicking on "square" and in the menu, clicking on "Rename Symbol".
• Update all of the function calls to use this new paramater with a comma.

Click for solution.

multiply(3, 6); multiply(2, 9);

3. Pass in some variables to multiply().

• Create some int variables in main.
• Pass in the variables to the multiply() function, by just saying their name instead of a number. Example: multiply(myNum,myNum2);

4. Try to pass in a decimal number (double or float) to multiply.

• multiply(2.3,6.1);
• The red squigglies on multiply read: The method multiply(int, int) in the type ParametersSolution is not applicable for the arguments (double, double). This is basically telling you that multiply MUST take in 2 ints, and cannot take in 2 doubles.

5. Duplicate (copy & paste) multiply, and modify it to take in 2 doubles, and name it multiplyDecimals.

• Try to change the multiply(2.3,6.1); into a multiplyDecimals(2.3,6.1);.

4. Problem with functions currently:

• What if you didn't want to just print out the result, but pass it into another function, or do something else rather than printing?

Return Values

1. Open Return.java, and look through the code.

• Run the code. What is it doing?
• The return keyword is put at the end of the function running. It is when the function is done running, and it gives a result.
• You can use the return value like a variable. This means, you can call the function wherever you would use a variable, even storing the return in a variable!

2. Remove the variables, replacing them with function calls in the code.

• Call square(5) and square(2) in place of squareFive and squareTwo in the println statement.
• Try adding more square() calls in code, like another print statement.

3. Assign the result from a square() to a float.

• Before running, what do you think will happen?
• Try fixing the function.
  • Remember - the paramater used in the template is a float.

Click for solution.

static float square(float num){ //code }
Turns into...
static int square(int num){ //code }