如何在 java 中调整二维数组的大小

Question

For context, I am working on an AI that classifies speech and ultimately controls a character in a video game. I have code that continuously samples audio and converts it into a spectrogram, but due to java threads being inaccurate the spectrograms don't have constant dimensions.

I have a 2D array of values that represent the spectrogram and I want to resize the array. The only current methods I've found aren't efficient enough as time is of the essence. For example, using BufferedImage objects and Image objects:

Image newImage = yourImage.getScaledInstance(newWidth, newHeight, Image.SCALE_DEFAULT);

Is there an algorithm I can implement that resizes the array of values, the same way an image is resized

Answer 1

Arrays in java cannot be resized at all. A 'resize' operation makes an entirely new array, copies the data over, and returns the newly created array.

Abstraction is the name of the game: For example, this:

List<String> list = new ArrayList<String>(1000);
for (int i = 0; i < 500; i++) list.add("Hello, " + i);

gives you a list with 500 things in it. If you then add 500 more, that will incur zero penalties.

There are a lot of collections already available in the java.util package, as well as java.util.concurrent . For more exotic needs, have a look at third party offerings; there are tons and tons of types out there for varied uses, including primitive collections, collections with guarantees about performance impact (arraylist has low cost but only if you consider costs amortized: From time to time an add call to an arraylist is expensive as it has to make new arrays. If that's a problem, there's a library for that - RealTime java needs this a lot, that might help when looking for appropriate implementations).

Note that you shouldn't worry about performance until you have a real life 'proof' that the code is running slower than you'd like. Then run profilers, and armed with a profiler report, look at only those areas that the profiler tells you are where the CPU and/or memory resources are being spent. There is no point optimizing parts of the code that are <1% of the total resource spend.

NB: And, for an encore.. "Resize an array in java" isn't a thing, and... 'A 2D array in java' also doesn't exist. You can have an array of arrays which is not quite the same thing and presumably what you have here. But that doesn't change the point: You need an abstraction that does what you want, and 'array' (or array of arrays) is not it.

Answer 2

Once you assigned a sized to an array in java you can't change it.Use Collections framework if you need to have a dynamic list size.