String.format doesn't have an effect on a String

Question

In the following code timeToDisplay.format seems to have no effect on the timeToDisplay String. tw.setText(timeToDisplay) displays milliseconds instead of expected MM:SS. I've rebuilded the project with no joy.

code:

 TextView tw = (TextView) getView().findViewById(R.id.textView_time);

            long millis = intent.getLongExtra("stamp", 0L);

            String timeToDisplay = String.valueOf(millis);
            timeToDisplay.format("%d min, %d sec",
                    TimeUnit.MILLISECONDS.toMinutes(millis),
                    TimeUnit.MILLISECONDS.toSeconds(millis) -
                            TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));

            tw.setText(timeToDisplay);

This boils down to **Read The Friendly Manual**. Your title is 100% accurate. — Jonathon Reinhart, Jan 14 '14 at 14:25
@chrylis provided the proper answer. format is a static method, so `String.format(` should be used. `timeToDisplay.format(` is syntactically correct but is misleading and discouraged. — Glenn Lane, Jan 14 '14 at 15:28
@Glenn Lane The answer have been accepted already and I'm not going to change it. Your downvoting the question and all of the answers won't change this either... — XorOrNor, Jan 14 '14 at 15:44
@soulreaver I haven't upvoted/downvoted... I've only deleted my own answer — Glenn Lane, Jan 14 '14 at 17:00

score 3 · Answer 1 · answered Jan 14 '14 at 14:22

3

Java strings are immutable. You have to assign the result back to a variable:

timeToDisplay = String.format(...);

In your case, you don't need to turn millis into a string at all; the formatter just needs the numbers that you're calculating for it.

answered Jan 14 '14 at 14:22

chrylis -cautiouslyoptimistic-

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score 0 · Answer 2 · answered Jan 14 '14 at 14:22

calling timeToDisplay.format() will NOT change your actual timeToDisplay reference. However, it will return the new string. Add this to your code:

String formattedTime = timeToDisplay.format("%d min, %d sec",
                TimeUnit.MILLISECONDS.toMinutes(millis),
                TimeUnit.MILLISECONDS.toSeconds(millis) -
                        TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));

Then, use formattedTime in your setText

score 0 · Answer 3 · answered Jan 14 '14 at 14:23

0

strings are immutable. try:

timeToDisplay = timeToDisplay.format("%d min, %d sec",
    TimeUnit.MILLISECONDS.toMinutes(millis),
    TimeUnit.MILLISECONDS.toSeconds(millis) -
    TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));

answered Jan 14 '14 at 14:23

Phantômaxx

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score 0 · Answer 4 · answered Jan 14 '14 at 14:25

tw.setText(timeToDisplay.format("%d min, %d sec",
                    TimeUnit.MILLISECONDS.toMinutes(millis),
                    TimeUnit.MILLISECONDS.toSeconds(millis) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis))));

Alternatively, you can assign the value of timeToDisplay.format("%d min, %d sec", TimeUnit.MILLISECONDS.toMinutes(millis), TimeUnit.MILLISECONDS.toSeconds(millis) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)))); to a variable and pass that to tw.setText().

score -1 · Accepted Answer · answered Jan 14 '14 at 14:22

Strings are immutable, you have to reassign it in this way:

timeToDisplay = timeToDisplay.format("%d min, %d sec",
                TimeUnit.MILLISECONDS.toMinutes(millis),
                TimeUnit.MILLISECONDS.toSeconds(millis) -
                        TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));

That means that the format method cant change timeToDisplay it only returns a new string which is formatted.

String.format doesn't have an effect on a String

5 Answers5