May 4, 2023

Methods

Overview

In this presentation we will discuss these 4 topics: Main method vs. Jeroo methods Choosing behaviors to turn into methods Writing a Jeroo method Preconditions and postconditions

Jeroo has many built-in methods Actions

hop, turn, … Sensor methods

isNet? isFlower? …

The programmer can define additional methods to extend the behavior of every Jeroo.

Behaviors and methods Behavior = an action that an object can take or a task it

can perform in response to a request from an external source

Method = Collection of statements written in a programming language to describe a specific behavior.

1st define and name a behavior 2nd write code for the method

Which parts of the program should be methods?

choose a behavior Any complex, well-defined step Any sequence of steps that more than 1 Jeroo will perform Any sequence of steps that occur several times.

A good behavior to turn into a method has a very clear definition and is used more than once in the program.

Writing the method

A Jeroo method contains the code describing what any Jeroo needs to do to carry out a particular behavior.

method method_name ( ){

} //== method_name==

•Choose a name that is meaningful

•Empty parenthesis required on the header line (first line)

•Indent code inside the method

Body of method

Containing statements that describe how any arbitrary Jeroo can carry out this particular behavior.

Important differences

Jeroo methods

Can be many other methods Choose your own names Must be called by the main

method Can’t instantiate in the

method

Main method

Only one main method Must be called main Always comes first Instantiate Jeroos

Example of a Jeroo method//

***********************************************************

//Turn Around: makes a Jeroo turn 180 degrees//

***********************************************************

method turnAround( ){

turn(LEFT);turn(LEFT);

} // === end turnAround ===

Good , descriptive name for the method

The code is indented

Comments clearly explain what the method does

Notice that no Jeroo name is specified in the steps

Everything in yellow is good!

Important difference

Jeroo methods

Define a behavior available to ALL Jeroos so do not specify which Jeroo performs the steps inside the method

Example in a Jeroo method for any Jeroo

pick(); hop(2); give(AHEAD);

Main method

All steps must specify which Jeroo does each action:objectname.method();

Example in main for a Jeroo named betty

betty.pick(); betty.hop(2); betty.give(AHEAD);

Using a Jeroo method After you write your code

Use it just like any other methodmethod main( ){

Jeroo ali = new Jeroo(5,5,8);ali.plantCorner( );

} // === main ===

method plantCorner( ){

plant();hop();turn(RIGHT);hop();plant();

} // === plant Corner ===

One method can call another The plantThree method is used twice in the

plantRectangle methodmethod plantThree( ){ plant( ); hop( ); plant( ); hop( ); plant( );} //=== plantThree ===method plantRectangle( ){

plantThree( );moveDown( );plantThree( );

}//=== plantRectangle ===

This code is

missing

most of its

comments!Defined above

Must also be defined somewhere

A

B

Preconditions and Postconditions A complete definition for a behavior includes: Preconditions

Assumptions of what is true before the method is called Postconditions

What will be true after the method is finished

In Jeroo, the only things that change are: island cells (flower planted, net gone…) Jeroo attributes (location, number of flowers …)

Things to consider when writing a precondition

What must be true for this method to work? Ask: does the Jeroo need

A certain number of flowers? To be facing a particular direction? To be in a certain location?

Ask: are the contents of certain island cells important?

//********************************************//Plant 3 flowers in a row starting at current location//PRECONDITIONS:// 1. There are 2 clear spaces directly in front// 2. Jeroo has at least 3 flowers//********************************************method plantThree( ){…

Things to consider when writing a postcondition

Describe what is true after the method finishes Ask: how will the method change

the number of flowers? the direction the Jeroo is facing? the Jeroo’s location?

Ask: have the contents of certain island cells changed?

// // POSTCONDITIONS:// 1. Three flowers have been planted, starting at the // beginning location and proceeding straight ahead// 2. The jeroo is standing on the last flower, // facing its original direction// ********************************************method plantThree( ){ …

The End