Convert int to byte array and print to console with System.out.write method

Question

I have this program:

public class Duplicates {
    public static void main(String[] args) {
        byte[] bytes = "hz".getBytes();
        for (int i = 0; i < 10_000_000; i++) {
            System.out.write(bytes, 0, bytes.length);
        }
    }
}

After start I have output:

hzhzhzhzhzhzhzhz.....hz

But if I try convert int to byte array and print:

public class Duplicates {
    public static void main(String[] args) {
        byte[] bytes = ByteBuffer.allocate(4).putInt(666).array();
        for (int i = 0; i < 10_000_000; i++) {
            System.out.write(bytes, 0, bytes.length);
        }
    }
}

After start I have output:

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

I want to print 666 10,000,000 times on each line of console and not use more than 20MB memory or 1 second.

What am I doing wrong?

EDIT If I will use example @Justin - Integer.toString(i).getBytes() I have this:

Jannik · Answer 1 · 2019-01-23T19:31:40.943

The problem you are facing is not the call to Integer.valueOf(666).toString() since it is executed only once. The actual problem is, that the call to System.out.write() has some overhead. This can be avoided by using a larger buffer which is filled with some repetitions of the input value.

Here is what I came up with:

long start = System.currentTimeMillis();
byte[] bytes = String.valueOf(666).getBytes();

// use 20 mb of memory for the output buffer
int size = 20 * 1000 * 1000  / bytes.length;


byte[] outBuffer = new byte[size * bytes.length];
// fill the buffer which is used for System.out.write()
for (int i = 0; i < size; i++) {
    System.arraycopy(bytes, 0, outBuffer, i * bytes.length, bytes.length);
}

// perform the actual writing with the larger buffer
int times = 10_000_000 / size;
for (int i = 0; i < times; i++) {
    System.out.write(outBuffer, 0, outBuffer.length);
}
long end = System.currentTimeMillis();
System.out.println();
System.out.println("Took " + (end - start) + "Millis");

Which takes about 600ms to output 666 ten million times.

score 0 · Answer 2 · edited Jan 23 '19 at 19:00

0

That looks correct. If you cast int 666 to a char, that's what would be displayed. If you want to literally print out 666, you would need to convert the int to a String first:

byte[] bytes = Integer.toString(input).getBytes();

edited Jan 23 '19 at 19:00

John Kugelman

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answered Jan 23 '19 at 18:44

Justin

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if that were enough I would have done so. I'm not just so freaked out. I cannot print lines in such a loop because there is another task that requires it. – ip696 Jan 23 '19 at 18:51
@ip696 I can't make sense of your comment. This answer seems to do exactly what you want. – John Kugelman Jan 23 '19 at 19:04
I edited the question especially for you – ip696 Jan 23 '19 at 19:07
What monitoring tool are you using? – Justin Jan 23 '19 at 19:17
I use JProfiler – ip696 Jan 23 '19 at 19:20
I will investigate further, but see if this helps also https://stackoverflow.com/questions/11823095/whats-the-fastest-way-to-output-a-string-to-system-out – Justin Jan 23 '19 at 19:25

Convert int to byte array and print to console with System.out.write method

2 Answers2