初始化大小为“ Long”数据类型的字节数组？

Question

So i have this method to read the data in a file into a byte array with starting point "offset" and length o "len" :

public static byte[] readFileDataToByteArray( File inFile, long offset, int len ) {

    byte[] buffer = new byte[ len ];

    try {
        RandomAccessFile in = new RandomAccessFile( inFile, "r" );
        in.seek( off );
        in.read( buffer );          
        in.close();
    } catch ( IOException e ) {
        System.err.println("Error readSentence: Error reading " + inFile ); 
        System.exit(1);
    }
    return buffer;
}

now this is working just fine as long as the len variable does not exceed the maximum allowed int value. but when I have to use "long" as data type of variable len to be able to pass larger numbers (ie to create lager arrays), I get the following error :

../util/Common.java:564: error: possible loss of precision
    byte[] buffer = new byte[ len ];
                              ^
required: int
found:    long
1 error

So basically all I need to do is to create a byte array with a size of a "long" data type. any hints ?

Answer 1

I have just tried. That the biggest array size can't exceed the heap size. So it's better to process the file in several time if it could be.

public class RandomAccessFileTest {
    static public class LargeArray {
        public long offset;
        public long len;
        public int arraySize; // can't exceed JVM heap size
        byte[] byte_arr;

        public LargeArray(long offset, long len, int arraySize) {
            this.offset = offset;
            this.len    = len;
            this.arraySize = arraySize;
        }
    }

    public static LargeArray readFileDataToByteArray(File inFile, LargeArray  array) {
        long count = array.len/array.arraySize;
        if (array.len > 0 ) {
            try{
                int arr_len = (count == 0) ? (int)array.len:array.arraySize;
                array.byte_arr = new byte[arr_len];
                RandomAccessFile in = new RandomAccessFile( inFile, "r" );
                in.seek( array.offset );
                in.read( array.byte_arr );          
                in.close();

                array.offset += arr_len;
                array.len    -= arr_len;
                return array;
            } catch ( IOException e ) {
                System.err.println("Error readSentence: Error reading " + inFile ); 
                System.exit(1);
            }       
        }
        return null;
    }

    public static void main(String[] args) {

        LargeArray array = new LargeArray(5,1000000, 10000);
        File file = new File("test.txt");

        while((array = readFileDataToByteArray(file, array)) != null) {
            System.out.println(new String(array.byte_arr));
        }   
    }
}

Answer 2

You can probably check out this link stackOverflow

A word of cauuion, always check out for the range of primitives before tycasting them. Here in you want a byte array size to take the long value which seems to me a invalid scenario since long can have precision in it's scope. Flooring/ceiling of the precision value would certainly result in loss of precision.