Java - Ch. 4 - Methods

Return types:

Example of a simple method:

public static int add(int x, int y) // This is called the method header

{

return x + y; // This method returns the value of x + y

}

• Examining the method header from the example above:

public static int add (int x, int y)

public static - Use this for every method for now.

int - This is the return type. This is the type of variable that the method returns

back to the program. It can be any variable type that we have worked with

add - Method name

int x, int y - This is the parameter list. It is a list of variables, along with their

types that are handed to the method.

How to call a method:

• Using the method in the example above, a full program could look like this:

public static void main(String[] args) // This is the main method that we always use

{

int a = 3;

int b = 100;

int c;

// Call the "add" method and set "c" equal to result. Here, a and b are

// known as the “actual parameters”.

c = add(a, b);

// Print c to the screen

System.out.print(a + " + " + b + " = " + c);

}

// This is the “add” method. Here, x and y are known as the “formal

// parameters”. Parameter a becomes x inside the method and parameter b becomes y.

public static int add(int x, int y)

{

return x + y;

}

OUTPUT: 3 + 100 = 103

(see handout: “I can’t feel my face when I’m with you” for examples of methods)

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Declare and initialize a boolean variable

// call the printBoolean method

}

public static void printBoolean (boolean x)

{

// prints the output to the screen

}

SAMPLE RUN:

true

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Create four variables, three with hard-coded values

int tom = 4;

int sara = 8;

int jack = 10;

int multAnswer;

// Call the method that multiplies the three variables together

// and assigns the result to “multAnswer”

multAnswer = mult3(tom, sara, jack);

// print “multAnswer” to the screen

}

public static int mult3(int pat, int emily, int zora)

{

// create the code that multiplies the parameters together and returns the answer

}

OUTPUT:

4 * 8 * 10 = 320

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Print a line requesting a boolean

// Assign the input to a variable called “origBoolean”

// Call the method and assign the returned value to a new variable like this:

boolean flipped = flipBoolean(origBoolean);

// Print the new variable

}

public static boolean flipBoolean (boolean x)

{

// returns the opposite of the boolean parameter (hint: use !x)

}

SAMPLE RUN #1:

Please give me a boolean (true or false):

true

The opposite of that boolean is false.

SAMPLE RUN #2:

Please give me a boolean (true or false):

false

The opposite of that boolean is true.

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Print a line requesting a number to be squared from the user

// Assign the input to a variable called “num”

// Call the method and hand it the variable. Assign the returned value to a

// new variable called squared like this:

int squared = square(num)

// print the value of squared

}

public static int square(int number)

{

// Returns the value of number squared

}

SAMPLE RUN #1:

What number would you like to square? (integer please)

4

That would be 16.

SAMPLE RUN #2:

What number would you like to square? (integer please)

10

That would be 100.

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// print a line showing a modulus example

// print a line asking for the dividend

// assign the dividend to a variable

// print a line asking for the divisor

// assign the divisor to a variable

// call the modulus method and hand it two parameters

// the result should be stored in a variable:

int mod = modulus(dividend, divisor)

// print the answer with proper formatting

}

public static int modulus (int divid, int divis)

{

// returns the answer of divid % divis

}

SAMPLE RUN:

Example of modulus: 5 % 2 = 1 where 5 is the dividend and 2 is the divisor.

Please give me the dividend:

18

Please give me the divisor:

4

18 % 4 = 2

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Print a line asking for a number

// Assign the number to a variable called “num1”

// Print a line asking for a number

// Assign the number to a variable called “num2”

// Say “Thanks!”

// Call the “add” method and hand it num1 and num2. Assign the result to a

// variable.

// Print the result to the screen with proper formatting

// Call the “mult” method and hand it num1 and num2. Assign the result to a

// variable.

// Print the result to the screen with proper formatting

// Call the “sub” method and hand it num1 and num2. Assign the result to a

// variable.

// Print the result to the screen with proper formatting

}

public static int add (int n1, int n2)

{

// return the answer of n1 + n2

}

public static int mult (int n1, int n2)

{

// return the answer of n1 * n2

}

public static int sub (int n1, int n2)

{

// return the answer of n1 - n2

}

SAMPLE RUN:

Please give me a number to do some math on:

7

Please give me a second number:

2

Thanks!

7 + 2 = 9

7 * 2 = 14

7 - 2 = 5

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Create thirteen variables, nine with hard-coded values

double firstBatch1 = 7.0;

double firstBatch2 = 10.0;

double firstBatch3 = 30.0;

double firstBatchAvg; // You could call the method here (answer: 15.6666)

double secondBatch1 = 4.0;

double secondBatch2 = 6.0;

double secondBatch3 = 6.0;

double secondBatchAvg; // You could call the method here (answer: 5.3333)

double thridBatch1 = 150.0;

double thirdBatch2 = 220.0;

double thirdBatch3 = 255.0;

double thirdBatchAvg; // You could call the method here (answer: 208.3333)

double allBatchAvg; // This will hold the average of the other three averages

// print “allBatchAvg” to the screen

}

public static double avg3(double x, double y, double z)

{

// create the code that returns the average of x, y and z.

}

OUTPUT:

The overall average is: 76.44 // If the decimals don’t match exactly, its ok

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Create the following variables:

String word1 = “The ”;

String word2 = “first ”;

String word3 = “sentence. ”

String word4 = “Now ”;

String word5 = “the “;

String word6 = “second. “

String sentence;

// Call joinStrings six times to create the entire sentence. The first time, hand it

// sentence and word1, the second time hand it sentence and word2, and so

// on….

}

public static String joinStrings(String sent, String newWord)

{

// create the code that adds “newWord” to the end of “sentence”.

// This is done by concatenating two Strings together.

}

OUTPUT:

The first sentence. Now the second.

PROGRAM STRUCTURE:

public static void main(String[] args)

{

// Take in all of the variables with appropriate variable names

// Say “Thank you. Here is your report card:”

// Call both methods below to generate the desired results

}

// The header goes here. The method is called avg, should take in three test grades and

// return the average of the test grades.

{

// Calculate and return the average of the three test grades

}

// The method header goes here. It is called printCard and should display the name,

// each test grade and the average, as displayed in the Sample Run.

{

// Print the relevant information. You can call the avg method when you need it

}

SAMPLE RUN:

Please enter your first name: Paul

Please enter your second name: Rudd

What did you get on your first test? 87

What did you get on your second test? 82

What did you get on your third test? 100

Thank you. Here is your report card:

Rudd, Paul

Test #1: 87

Test #2: 82

Test #3: 100

Average: 90