我应该在Java程序中使用多少内存？

Question

I am making a Java program. It involves making a image with size up to 9933 * 14043 pixels (which is A0 size and 300 ppi). The image is 24 bit, so it would take up about 400mb of space. The BufferedImage class some how take more RAM than the bitmap's actual size, so the image would comsume about 600 mb of RAM. With other data, the app would at max take about 700 mb of ram when rendering the large image. I haven't had any problem with it so far. However, if the end user doesn't have enough free ram, the JVM will not be able to allocate the memory for the bitmap and will throw an OutOfMemoryError.

So what should I do?

I came up with something:

1. Catch the error and throw prompt to the user.
2. Wait some time until here's enough memory. If the waiting last too long, throw prompt.
3. Write my own bitmap class, and write the image by part with an FileOutputStream. The .bmp format is not terribly complicated. (Actually I already wrote and optimized most of it.) By rendering the bitmap by part, the whole image doesn't have to stay in RAM. The size of the parts can be changed dynamically according to the available memory size. However this is kind of reinventing the wheel and takes a significant amount of work. Also, the part of the image that involves text must be placed into a BufferedImage and then converted to my class (because I don't want to look into the true font format). Anyway, if the Java BufferedImage class works in my case, I wouldn't go down this way.

Answer 1

I doubt that anyone has less than a gig of ram nowadays. So you can check if the user has enough memory with Runtime.getRuntime().maxMemory() , and if they don't just show an error and close. Here's an example that uses JOptionPane in the case of an error:

long memory = Runtime.getRuntime().maxMemory(); //in bytes
long required = 700 * 1024 * 1024; //700MB, in bytes
if(memory < required) {
    JOptionPane.showMessageDialog(null, "You don't have enough memory. (700MB required)", "Error", JOptionPane.ERROR_MESSAGE);
    System.exit(0);
}

maxMemory() returns the maximum amount of memory the JVM will attempt to use (in bytes).