Download Progress Calculator

Here is my progress calculator class. It is used for downloads/uploads. It takes bytes in and calculates the percentage(to the nearest 5%) that should show on a progress bar. Please let me know how I could improve it. Thanks a lot!!

```
public class ProgressCalculator {

private int totalAmount;
private int progressAmount;
private int amountProgressItems;
private int progressBarPercentage;

//returns if the progress bar needs to change
public boolean progress(int amount) {
progressAmount = progressAmount + amount;
return updateProgressbarPercentage();
}

public int getCurrentValue() {
return progressBarPercentage;
}

//returns if the progressbar needs to change
public boolean addProgressItem(int itemAmount) {
totalAmount = totalAmount + itemAmount;
amountProgressItems++;
return updateProgressbarPercentage();
}

//returns true if has been updated;
private boolean updateProgressbarPercentage() {
int newProgressBarPercentage = round(calculateProgressPercentage());
if (progressBarPercentage == newProgressBarPercentage) {
return false;
} else {
progressBarPercentage = newProgressBarPercentage;
return true;
}
}

public int getAmountOfItems() {
return amountProgressItems;
}

public boolean removeProgressItem(int byteAmount) {
if (amountProgressItems > 0) {
totalAmount = totalAmount - byteAmount;
amountProgressItems--;
}
return updateProgressbarPercentage();
}

private int calculateProgressPercentage() {
double x = progressAmount;
double y = totalAmount;
double result = (x / y) * 100;
return (int) result;
}

private int round(int num) {
int temp = num % 5;
if (temp < 3)
return num - temp;
else
return num + 5 - temp;
}

public void

It's really hard to tell what this class does. From what you say, I feel like you have a number of TransferTasks and want to have a sort of ProgressTracker for them. So, as for me, your goal is to make user's code look like this:

ProgressTracker progressTracker = new ProgressTracker();
progressTracker.setListener(new ProgressTrackerListener() {
  @Override
  public void onProgressChanged(double progressPercentage) {
    // TODO: update your UI here
  }
});
...
TransferTask transferTask = new UploadTask("/home/jiduvah/1.txt");
progressTracker.track(transferTask);
transferTask.start();

Why? Because it doesn't need any comments to describe what happens here: you just write it in English.

Update - In case you're absolutely sure you like your approach.

First, in this code:

private int round(int num) {
    int temp = num % 5;
    if (temp < 3)
        return num - temp;
    else
        return num + 5 - temp;
}

I see magic like 5 and 3. Looks like it does exactly what you need to do, and you've even wrote about meaning of 5, but 3 is still a mystery.

Then:

double x = progressAmount;
double y = totalAmount;
double result = (x / y) * 100;
return (int) result;

When you divide int by int, you get int. When you divide int by double or double by int, you get double. So you may just write:

double result = 100 * progressAmount / (double)totalAmount;

Regarding the whole idea, I'm not sure whether this code works at all, because it's hard to understand how one should use it.

StackExchange Code Review Q#13121, answer score: 4