Question

Homework Help:
Exercise 7.31 and 7.32 in Java.
Exercise 7.31* Write a method public WorkerList highOnes() in WorkerList: The executor returns a new WorkerList object containing only its Worker objects whose pay is above average.
7.32 is in comments

Answer 1

Exercise 7.32* Write a method public void addAll (WorkerList given) in WorkerList: The executor adds all the Worker values from a WorkerList parameter to its own list, stopping only if its array becomes full. Throw an Exception if given is null.

Answer 2

@woodrow73 :)

Answer 3

I'm having trouble on how to do 7.32. I finished 7.31 today. :)

Answer 4

Book WorkerList:

public class WorkerList
{
private Worker[ ] itsItem;
private int itsSize = 0;

/** Create an empty list capable of holding max Workers. */
public WorkerList (int max)
{ itsItem = (max > 5) ? new Worker[max] : new Worker[5]; //1
} //======================

/** Add all Worker values in the non-null file to this list,
* except no more than there is room for in the list. */
public void addFromFile (Buffin file)
{ Worker data = new Worker (file.readLine()); //2
while (data.getName() != null && itsSize < itsItem.length)
{ itsItem[itsSize] = data; //4
itsSize++; //5
data = new Worker (file.readLine()); //6
} //7
} //======================

/** Return the average pay for all workers in the list.
* Return zero if the list is empty. */
public double getAverage()
{ double totalPay = 0; //8
for (int k = 0; k < itsSize; k++) //9
totalPay += itsItem[k].seeWeeksPay(); //10
return itsSize == 0 ? 0.0 : totalPay / itsSize; //11
} //======================

/** Return names of workers making more than the cutoff. */
public String thosePaidOver (double cutoff)
{ String s = ""; //12
for (int k = 0; k < itsSize; k++) //13
{ if (itsItem[k].seeWeeksPay() > cutoff) //14
s += itsItem[k].toString() + "\n"; //15
} //16
return s; //17
}

Answer 5

Sure, so what's tripping you up?

Answer 6

I tripped on the logic for the executor to ad all the Worker values from a WorkerList parameter to its own list.

Answer 7

Do you need to use Arrays for this assignment? ArrayList would make life easier

Answer 8

I started like this:

ublic void addAll (WorkerList given)
{
Worker[] cool = new Worker[itsSize];

Answer 9

Yes, I do need arrays :)

Answer 10

Well you're going to need a loop; and to keep adding the parameter WorkerList array elements until either *this* instance's isItem[] array is full, or you run out of the parameter WorkerList array elements to add

Answer 11

for loop?
for (int k = 0; k < itsSize; k++)
{

Answer 12

you can probably take care of stopping the loop pretty easy with a for loop once the parameter WorkerList has looped through all it's elements.

Remember, you're dealing with multiple instances of the class - itsSize will refer to the size of the current instance, to get the size of the parameter WorkerList, you'll have to reference it via the object, like:
```
for (int k = 0; k < given.itsSize; k++)
```

Answer 13

okay, I get that.
Now,
we can do an if statement for the next part.

Answer 14

Since you're adding to the array in this instance, it's probably safest to figure out which elements currently aren't holding a value - that way we know both what elements we can add to, and how many elements max we can add - something like this; (also it's good practice to reference by an array's size by the array directly, not a different data value)
```
public void addAll (WorkerList given)
{
ArrayList<Integer> freeElements = new ArrayList<Integer>();
for(int i = 0; i < itsItem.length; i++) {
if(itsItem[i] == null)
freeElements.add(i);
}
for (int k = 0; k < given.itsItem.length && k < freeElements.size(); k++) {
itsItem[freeElements.get(i)] = given.itsItem[i];

}

}
```
So now it will stop looping once this instance of WorkerList is full, or we run out of elements from the given object. The next step is ensuring that given.itsItem[i]; isn't null

Answer 15

okay,
Can we do that in an if statement, as in
if (given.itsItem[I] == null)
then it goes out
else

Answer 16

Your teacher wants an exception to be thrown if any of the given itsItem array elements are null I think, right?

Answer 17

wait.. after re-reading the question, she wants an exception to be thrown if given is null, not it's itsItem arrays

Answer 18

You'll need a try/catch block if you're familiar with those.

Answer 19

no, I'm not familiar with those .

Answer 20

So null is basically a lack of value.. it was never initialized -- so what do you think happens if a null usage like this happens:
```
WorkerList wl;
System.out.println(String.valueOf(wl.itsItem.length));
```

Answer 21

the program could exit out......

Answer 22

I'd recommend
```
public void addAll (WorkerList given)
{
ArrayList<Integer> freeElements = new ArrayList<Integer>();
for(int i = 0; i < itsItem.length; i++) {
if(itsItem[i] == null)
freeElements.add(i);
}
try{
for (int k = 0; k < given.itsItem.length && k < freeElements.size(); k++) {
itsItem[freeElements.get(i)] = given.itsItem[i];

}
}catch(NullPointerException e) { e.printStackTrace(); }
}

```

Answer 23

if given is null, the code will immediately jump to what's in the catch statement when given.itsItem.length is called

Answer 24

I agree.
Thanks for the help :)

Answer 25

And e.printStackTrace(); will print out a cohesive-esque error report to console -- and I know I already said it, but the homework code is an abomination.. bad coding practice. I'd almost rewrite it for perfection...

Answer 26

The stuff your teacher is giving you