calling methods. review we can declare and create objects: dinosaur dino; dino = new dinosaur(); ...

Calling MethodsCalling Methods

ReviewReview We can declare and create objects:We can declare and create objects:

Dinosaur dino;Dinosaur dino;

dino = new Dinosaur();dino = new Dinosaur(); We can also shortcut the first two lines:We can also shortcut the first two lines:

Dinosaur dino = new Dinosaur();Dinosaur dino = new Dinosaur(); We can declare and create primitives:We can declare and create primitives:

double myArea = 54.2*24;double myArea = 54.2*24;

MethodsMethods

Another name for Another name for ““BehaviorsBehaviors”” Methods are small pieces of code Methods are small pieces of code

that can be used in other pieces of that can be used in other pieces of code.code.

They have 0 or more inputs, and 0 They have 0 or more inputs, and 0 or 1 output.or 1 output.

Why Methods?Why Methods?

Allows you to break up a hard problem Allows you to break up a hard problem into smaller, more manageable partsinto smaller, more manageable parts

Makes your code easier to understandMakes your code easier to understand Makes part of the code reusable so that Makes part of the code reusable so that

you:you: Only have to type it out onceOnly have to type it out once Can debug it all at onceCan debug it all at once Can make changes in one placeCan make changes in one place

How to use methodsHow to use methods

First, you must know what behaviors a First, you must know what behaviors a class has.class has.

You need:You need: An object that has the right behaviorAn object that has the right behavior The name of the behaviorThe name of the behavior What inputs it needs, if anyWhat inputs it needs, if any What output it gives, if anyWhat output it gives, if any

Example with a PictureExample with a Picture

Accountant:

getPayment

double (debt amount)

int (length of loan)

double (interest rate)

double (payment)

What it means:The Accountant class has a behavior, getPayment.It takes three inputs and gives one output.

Remember: Any number of inputs, but only zero or one output.

Call the methodCall the method

Accountant:

getPayment




double (payment)

First, you need an Accountant:

Accountant harry = new Accountant();

Four easy steps: Four easy steps: 1. Output1. Output

Accountant:

getPayment




double (payment)


Make a variable that will hold the output. If there is no output, skip this step.

double pay =

Four easy steps: Four easy steps: 2. Object2. Object

Accountant:

getPayment




double (payment)


Write the name of the OBJECT that has the correct behavior and then a period (or dot).

double pay = harry.

Four easy steps: Four easy steps: 3. Name of Method3. Name of Method

Accountant:

getPayment




double (payment)


Write the name of the method, followed by parentheses & semicolon.

double pay = harry.getPayment();

Four easy steps: Four easy steps: 4. Inputs4. Inputs

Accountant:

getPayment




double (payment)


In the parentheses, provide the input values in the same order. Give actual values, not the types! If no inputs are needed, skip this step.

double pay = harry.getPayment(3200, 14, .03);

Try this one:Try this one:

Calculator:

sqRoot

int (any number)

double (square root of original number)

Use the behavior to calculate the square root of 14. Don’t forget that you also have to create a Calculator object to do the job.

Did you get it?Did you get it?

Calculator:

sqRoot

int (any number)

double (square root of original number)

Calculator calc = new Calculator();

double root = calc.sqRoot(14);

Objects as input and Objects as input and outputoutput

Registrar:

makeForm

Transcript (gives student history)

Need to create the object that has the behavior as well as any objects that are used as input.

Registrar harry = new Registrar();Transcript stud123 = new Transcript();

Form (to send with applications)

Objects as input and Objects as input and outputoutput

Registrar:

makeForm

Transcript (gives student history)

Now follow the steps:Registrar harry = new Registrar();Transcript stud123 = new Transcript();

Form app = harry.makeForm(stud123);

Form (to send with applications)

Missing stepsMissing steps

Printer:

printOut

Form (what to print)

Form register = new Form();Printer myHP = new Printer();

myHP.printOut(register);


Student:

getHours

int (number of credit hours complete)

Student fred = new Student();

int hours = fred.getHours();


Student:

printHours

Student fred = new Student();

fred.printHours();


If you are calling a method in the same object as it was written, you can skip the dot and name part:

printHours();int hours = getHours();

But…But…

How do you know what the parts are? How do you know what the parts are? (There aren’t any pictures in the code)(There aren’t any pictures in the code)

Look at where the method is written for Look at where the method is written for the method HEADER:the method HEADER:

Java MethodsJava Methods

public int average(int num1, int num2){public int average(int num1, int num2){int result = 0;int result = 0;result = num1 + num2;result = num1 + num2;result = result/2;result = result/2;return result;return result;

}}

Modifiers OutputType Method

Name

Input TypesInput Names

Body

How to give output

Method header

Method HeadersMethod Headers

public class Calculator{public class Calculator{

public int average(int num1, int num2){public int average(int num1, int num2){

Calculator

average

int (first number)

int (second number)int (average)

Arguments or ParametersArguments or Parameters

The inputs to a method are called The inputs to a method are called argumentsarguments or or parametersparameters..

Parameters must appear in the order and Parameters must appear in the order and types specified at the top of the methodtypes specified at the top of the method

OutputsOutputs The type of output for the method is given The type of output for the method is given

in the method header.in the method header. If the method has no output, its return type If the method has no output, its return type

is is voidvoid. . Printer:

printOut

Form (what to print)

public class Printer{

public void printOut(Form toPrint){

Create the Method Create the Method HeadersHeaders

Your code will:Your code will: Average three integersAverage three integers Convert a Celsius temperature to FahrenheitConvert a Celsius temperature to Fahrenheit Draw a smiley faceDraw a smiley face Print any String any number of timesPrint any String any number of times Reverse a wordReverse a word Tell whether or not a number is evenTell whether or not a number is even Give the first three letters of a StringGive the first three letters of a String

Practice calling methodsPractice calling methods Calculator:Calculator:

Average three integersAverage three integers Convert a Celsius temperature to FahrenheitConvert a Celsius temperature to Fahrenheit

Printer:Printer: Draw a smiley faceDraw a smiley face Print any String any number of timesPrint any String any number of times

Utility:Utility: Reverse a wordReverse a word Tell whether or not a number is evenTell whether or not a number is even Give the first three letters of a StringGive the first three letters of a String

calling methods. review we can declare and create objects: dinosaur dino; dino = new dinosaur(); ...

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