www.valoxo.ch mock01a.html Q12

[Dmitry Golynkin]

code:
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import java.io.*;
public class Question12 {
public static void main(String[] args) throws IOException{
RandomAccessFile raf = new RandomAccessFile("test.dat","rw");
raf.writeInt(0x01);
raf.writeShort(0x23);
raf.writeByte(0x45); //line1
raf.seek(3);
short a1 = raf.readShort();
short a2 = raf.readShort();
System.out.println("0x"+Integer.toHexString(a1)+", 0x"+Integer.toHexString(a2));
}
}
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Hi friends! Thanks for previous help!
What is a full presentation of raf after line 1?

[Barry Gaunt]

www.valoxco.ch ???

[Barry Gaunt]

Warning MFU!
This is wrong (I should have read the API and run the code ):

High end  45 00 | 23 00 | 00 00 01 Low end
assert (a1 == 0x2300) && (a2 == 0x4500);

[ August 26, 2002: Message edited by: Barry Gaunt ]

[Anselme Bender]

This could help :
http://www.valoxo.ch/jr/mocks/mock01a.html

[Valentin Crettaz]

Dmitry,
please find below the explanation I have included in my mock exam about Question 12:

We write one int (4 bytes), one short (2 bytes) and one byte (1 byte). Then, we read 2 shorts. What you should do in cases like this is write what is actually written in the file. Here goes: First an int 0x00000001 (remember that an int is 32 bits long), then a short 0x0023 and finally a byte 0x45. test.dat now contains 00000001002345. We place the file pointer on the 3rd byte, let's say we remove what comes before the 3rd byte, we end up with 01002345. Now we read 2 shorts, that is, 0100 and 2345.
Remember that all this is in hexadecimal notation and thus 0x45 represents 1 byte (that is 8 bits). Moreover, when using hexadecimal notation, remember that each digit stands for 4 bits, thus 0x45 is actually 0100 0101.

[Dmitry Golynkin]

Thank you Valentin.

[Barkat Mardhani]

Hi Val:
Under which test objective this question will fall? How many such questions we can expect in 1.4 exam?
Thanks
Barkat
[ August 26, 2002: Message edited by: Barkat Mardhani ]

[Valentin Crettaz]

Those kinds of questions will not appear in the 1.4 version since IO has been dropped...

[Barkat Mardhani]

Hi Val:
If I am not conversant of Hex, binary, octal codes, Would that be ok for exam 1.4 as well?
Thanks
[ August 26, 2002: Message edited by: Barkat Mardhani ]

[Valentin Crettaz]

The new objectives for SCJP 1.4 state:

State the range of all primitive formats, data types and declare literal values for String and all primitive types using all permitted formats bases and representations.

which makes clear that you have to know how to represent integer values in hexadecimal, octal and binary forms.

[Barry Gaunt]

public final void writeInt(int v)
                    throws IOException

Writes an int to the file as four bytes, high byte first. The write starts at the current position of the file pointer.
That high byte first got me, folks!
-Sorry
[ August 26, 2002: Message edited by: Barry Gaunt ]