Organizing Your Code With Methods

Definitions

• Method
  • A named section of a program that performs a specific task.
  • Methods often return output when provided input. The example below computes the addition of two numbers, a and b.

    double add(double a, double b) {
       return a + b;
    }
    

  • They have the following general form: [return type] [name]([argument type] [argument name]). A method can have any number of arguments separated by commas, including 0.
  • Therefore, the above example has a return type of double, a name of add, an argument type of double two doubles, and argument names a and b.
  • Methods can also return void (which means nothing) and in this case do not require a return statement.
  • Use methods to organize your code by grouping related code together.
  • Use methods to reduce duplication of code for operations that must be performed many times.
  • You are already familiar with methods through your experience with System.out.println() and Math.abs().

Exercise #1

• Below is a Java program designed to print out where each member of the team goes to school:

  public final class Main {
    private Main() {
    }
      
    public static void printNameAndSchool(String fName, String lName, String school){
        // Add your code here.
    }
  
    public static void main(String[] args) {
        String firstName  = "John";
        String lastName = "Smith";
        String school = "King";
        System.out.println(firstName+" "+lastName+" goes to "+school);
  
        firstName  = "Jane";
        lastName = "Smith";
        school = "MSL";
        System.out.println(firstName+" "+lastName+" goes to "+school);
    }
  }
  

• Create a new folder called MethodExercise in C:\dev that has a Main.java file.
• Copy the above code into that file and Run to see the output.
• Modify the names and schools to match your group and add new code if needed for additional members.
• Complete the method:
  • printNameAndSchool(String first, String last, String school) that returns nothing (void)
  • It should print the statement “fName lName goes to school” where fName, lName, and school are the values of the input variables.
• Update your main method to call printNameAndSchool() instead of printing each statement itself.
  • Hint: In your main() method you should have only as many lines of code as you have members in your group.
  • Check with a mentor when complete to see if you can simplify your code even more.
  • The program should have the exact same output as when you didn’t use a method.

Exercise #2

• Add two new methods to your code:
  • public static int mean(int a, int b)
  • public static double mean(double a, double b)
  • Each method should compute the average of two numbers.
• From your main() method call each of your new functions and print the result:
  • Example: System.out.println(mean(1,2)); and System.out.println(mean(1.0,2.0);
• Run your program! Why do you get different results?

Exercise #3

• Add two new methods to your code:
  • public static int min(int a, int b)
    • This method should compute the minimum of two numbers a, b (Hint: Use conditionals!)
  • public static int max(int a, int b)
    • This method should compute the maximum of two numbers a, b (Hint: Also use conditionals!)
• From your main() method call each of your new functions and print the result:
  • Example: System.out.println(min(1,5)); and System.out.println(max(1,5);
• Run your program! Do your results make sense? Try different values to test it more.

Bonus Exercise

• Create a new file named Methods.java and copy the following code into the file:

 public final class Methods {

  public static double checkIfNumberIsGreater(double x, double y) {
    System.out.println("---------Cool Number Thing----------\n");
    // Fill in your method here
    
    // Think back to if/else statements. Call someone over if you need help.
    
    // Create code to check if x is greater than y, and if true, 
    // add 2 to x (x = x + 2), then print out "x is greater than y"
    
    // Then create code that adds 1 to y if it is greater than x,
    // and then print out "x is NOT greater than y"
    
    double z = 0;
    // Then set z equal to the sum of x and y
    System.out.println("The sum of x and y is: " + z + "\n");
    return z; 
  }

  public static void main(String... args) {
    double a = 9.4;
    double b = 8.7;

    // Replace this line with a call to checkIfNumberIsGreater() and pass a and b as parameters.
    // Then save the result in a double named c.

    a += c;
    b = b + (2.5 * c);

    // Call the method checkIfNumberIsGreater() here and pass a and b as parameters again.
  }
}