Hi again guys. Just putting that in, firstly, what does typecast mean? And when i compile what Danpost and then davmac put it tells me that worldWorld (sorry about name will change that) is not a variable. Do I have to make it first?
mattjames wrote ...
2013/8/28
Help Please
This is what I looks like if that helps
import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
/**
* Write a description of class robottrackslarge here.
*
* @author (your name)
* @version (a version number or a date)
*/
public class robot extends Actor
{
public void addedToWorld(World w)
{
worldWorld = (world) w;
counter3 = w.getCounter3();
choice = counter3.getCount();
}
private Counter2 theCounter2;
private Counter theCounter;
private int maximumcarrying=0;
private int score=0;
private int scorelevelone=150;//this sets the score
private int scoreleveltwo=150;
private boolean win=false;
private int targetscore; //may need to remove this
private int level=1;
private int passengersleft=4;
private int passengerscarrying=0;
//need to use this to set maximum bay size!!!!!!!!!!!
/**
* Act - do whatever the robot wants to do. This method is called whenever
* the 'Act' or 'Run' button gets pressed in the environment.
*/
public void act()
{
scoretester();// Add your action code here.
}
//maybe try using a boolean to see whether the game has been won
public void setcounter(){ //this will decide whether to keep the counter at 150 or lower it to 130
if (level==2){
world worldWorld = (world) getWorld();
Counter counter = worldWorld.getCounter();
counter.bumpCount(-20);
scoretester();
}
else{
scoretester();
}
}
A "typecast" is when you put a class name in parentheses before some expression to tell the compiler that you know the specific type that it will return. So, in:
... there is a typecast - (world) - to tell the compiler that you know that getWorld() will return a world (normally it returns a World). Without the typecast you get an error when you try to compile, because you can't assign a World value to a world variable.
Please, please, rename your 'world' class.
When you get an error and want help with it, please say which line the error occurs on.
world worldWorld = (world) getWorld();
Change lines 13 and 14 in you last code post to:
The first line creates a field that holds a 'world' object and assigns it the parameter value that is an object of type 'World' typecast to a 'world' object. The second line would fail if you tried to call 'getCounter3' on an object of type 'World' because the compiler does not know to look in the 'world' class for that method.
world worldWorld = (world) w; counter3 = worldWorld.getCounter3();
I'm sorry I will change the world name in a second. However there is still a problem with the code (indicated by the comment):
import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
/**
* Write a description of class robottrackslarge here.
*
* @author (your name)
* @version (a version number or a date)
*/
public class robot extends Actor
{
public void addedToWorld(World w)
{
world worldWorld = (world) w;
counter3 = worldWorld.getCounter3(); //error displays "cannot find variable counter 3"
choice = counter3.getCount();
} You need to instruct the compiler what type of data the field 'counter3' is to hold. This is done any time you declare a new field. 'counter3' is to be a new field in the robot class 'addedToWorld' method (because it is not declared in the class itself, it will be localized to the method).
// change line 14 to Counter counter3 = worldWorld.getCounter3();
New error (sorry about this!)
import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
/**
* Write a description of class robottrackslarge here.
*
* @author (your name)
* @version (a version number or a date)
*/
public class robot extends Actor
{
public void addedToWorld(World w)
{
world worldWorld = (world) w;
Counter counter3 = worldWorld.getCounter3(); //incompatible types, found Counter3 but expected Counter
choice = counter3.getCount();
} Yeah, I forgot you created separate classes for each type counter.
//change line 14 to Counter3 counter3 = worldWorld.getCounter3();
That worked but there is a new problem now:
import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
/**
* Write a description of class robottrackslarge here.
*
* @author (your name)
* @version (a version number or a date)
*/
public class robot extends Actor
{
public void addedToWorld(World w)
{
world worldWorld = (world) w;
Counter3 counter3 = worldWorld.getCounter3(); //fine now!
choice = counter3.getCount(); //cannot find symbol - variable choiceThat will also need to be declared as it also is a new field for the method.
int choice = counter3.getCount();
Thank you that worked however this has now popped up: further on in the same actor I have this code
and it says it cannot find the variable choice. Is this because they are in different {public void...} brackets? How do I combat this?
public void scoring(){
//insert code here to check modification and then reduce accordingly
if (choice==1){ //it says it cannot find choice
world worldWorld = (world) getWorld();
Counter counter = worldWorld.getCounter();
counter.bumpCount(-5);
passengerpickuptester();
}
}
Is it not possible that the Counter3 object value could change? and when it does, the scoring will be different?
No it doesn't change it only changes at the start before the actor with scoring in is initialised.
In that case, it will not hurt to add an instance field in the 'robot' class to hold the value.
Remove the 'int' we added to the 'choice' assignment line and add
outside any method, but still inside the class.
You are correct, fields declared in one method are not available for use in others unless somehow passed between the two. Once a method is finished executing, any and all fields declared within it that are not stored anywhere else are no longer accessible. All fields declared in the class outside of any method can be accessed by any method within the class. Their accessibility by other classes and scope (when they are destroyed or reset) are determined by the modifiers you place in the field declaration statement. The section on Classes and Objects in the Java tutorials might be something to review.
private int choice;
matt james need help with my report asap!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! plz email me mez1998@aol.com
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