Java：在不知道确切执行时间的情况下使用进度条

Question

I have been reading for a while about progress bars, but I still can't find the answer to my question. Maybe it is something that I haven't realized.

http://docs.oracle.com/javase/tutorial/uiswing/components/progress.html

I have a program written in java, where I also calculate the time needed to be finished, using

static long startTime = System.currentTimeMillis();
...
long endTime   = System.currentTimeMillis();
long totalTime = endTime - startTime;
System.out.println(totalTime);

I would like to know, if it possible to create a progress bar, with the percentage of the program that is completed. I am really confused, because I don't know if I can calculate the time needed before the execution.

I would appreciate any help. Regards

Answer 1

A progress par doesn't show the percentage of time elapsed but the percentage of work .

So if your code needs to process 470 objects (= max value). Each time an object is processed, increment progress by 1.

Answer 2

You need some way to measure the progress of your task. Are you processing a known amount of data? You should be able to calculate how much progress you have made and then periodically update your progress bar with the new value. For example set up you progress bar to have a range of 0 to 100.

JProgressBar myProgressBar = new JProgressBar(0, 100);

As you process your data (in a new thread), update your progress bar in the Swing thread:

int[] myData = // data to process

for (int ctr = 0; ctr < myData.length; ctr++) {
    doMyProcess(myData[ctr]);
    int percentComplete = (int)Math.round(ctr / (float)myData.length);
    myProgressBar.setValue(percentComplete);
}

If you cannot measure your progress in some way, then you will need to use an "indeterminate" progress bar, which will indicate that your program is doing something, but the task is not measurable.

myProgressBar.setIndeterminate(true);

Answer 3

It's quite hard to estimate time needed for program to finish. But maybe you should rather concentrate on data set you're processing (files you're copying, database rows you're processing, etc...) and measure that instead? It's something you probably know and can calculate completed percentage out of it. If you really don't have a finite data set, then maybe you should show a indeterminate progress bar instead of showing user a progress bar that doesn't give any meaningful information.

Answer 4

What you need in this case is indeterminate ProgrssBar . Here is a paragraph from official documentation :

Sometimes you can't immediately determine the length of a long-running task, or the task might stay stuck at the same state of completion for a long time. You can show work without measurable progress by putting the progress bar in indeterminate mode. A progress bar in indeterminate mode displays animation to indicate that work is occurring. As soon as the progress bar can display more meaningful information, you should switch it back into its default, determinate mode.

Below is the snippet to use ProgressBar in indeterminate mode

public void propertyChange(PropertyChangeEvent evt) {
if (!done) {
    int progress = task.getProgress();
    if (progress == 0) {
        progressBar.setIndeterminate(true);
        taskOutput.append("No progress yet\n");
    } else {
        progressBar.setIndeterminate(false); 
        progressBar.setString(null);
        progressBar.setValue(progress);
        taskOutput.append(String.format(
                "Completed %d%% of task.\n", progress));
    }
}
}

The snippet has been taken from here .