java: saving data into an array

Question

I'm trying to save some data into an array but unfortunately all the data is saving into array[0] while it shouldn't be like this normally.

int j = 0;
while ( j < data.length ) { 
    float unbin = binary(data[2*j+1])+binary(data[2*j]);
    float[] bin = new float[] {unbin};
    print(bin);
    j = j + 2;
}

it wrote all the data in bin[0] , what's wrong with my code ?

how could I write :

bin[j] = unbin ?

to save the data in in bin[0] while j = 0 and so on ?

here is the updated code :

    int j = 0 ;
  float[] bin1 = new float[(data.length/2)];
  while (j < data.length ) {
    if ( data[2*j+2] >= 0  ) {

      String unhx =(binary(data[2*j+3])+binary(data[2*j+2])+binary(data[2*j+1])+binary(data[2*j]));
      float unbin = ((float)unbinary(unhx)/100);
      bin1[j/2] = unbin;
      print(bin1[1]);
    }

    else if  ( data[2*j+2] < 0 && data[2*j+3] < 0 ) {
      data[2*j] = (byte)(-data[2*j]);
      data[2*j+1] = (byte)(-data[2*j+1]);
      String unhx =(binary(data[2*j+1])+binary(data[2*j]));
      float unbin = ((-1)*(float)unbinary(unhx)/100);
      bin1[j/2] = unbin;
      print(bin1[1]);
      }
      j = j + 2;
  }

Why are you skipping every second pair of data?

Peter Lawrey
– Peter Lawrey

2012-06-14 13:39:58 +00:00
Commented Jun 14, 2012 at 13:39 — Peter Lawrey
– Peter Lawrey, Commented Jun 14, 2012 at 13:39

Jon Skeet · Accepted Answer · 2012-06-14 13:33:50Z

7

You're creating a new array (of length 1) on each iteration. You need to create the array before the while loop:

float[] bin = new float[...];
while (...) {
    ...
    bin[j] = unbin;
}

(It's unclear what the length should be here - I suspect you don't want to be multiplying j by 2 and incrementing it by 2 each time.)

answered Jun 14, 2012 at 13:33

Jon Skeet

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4 Comments

melisa zand Over a year ago

when I define bin outside the loop it gives me incompatible type error .

Jon Skeet Over a year ago

@melisazand: Well you haven't given us even nearly enough information to understand why or where, which makes it very hard to help you further.

melisa zand Over a year ago

it's part of this question : stackoverflow.com/questions/11033375/…

Jon Skeet Over a year ago

@melisazand: That doesn't help really, as you still haven't shown us the code that fails to compile via my suggestion. Please read tinyurl.com/so-hints for future questions.

Jeff Watkins · Accepted Answer · 2012-06-14 13:34:23Z

2

Bin is scoped inside your loop. It is recreated each time with a single element e.g. {unbin}.

It would appear that you want to convert a binary item which is two bytes long into a float upon each iteration.

int j = 0;

float[] bin = new float[(data.length/2)];

while ( j < data.length ) { 
    float unbin = binary(data[2*j+1])+binary(data[2*j]);   
    bin[j/2] = unbin;
    j += 2;
}

answered Jun 14, 2012 at 13:34

Jeff Watkins

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Comments

ShWebb · Accepted Answer · 2012-06-14 13:40:01Z

2

First, You need to declare the bin array BEFORE the loop (so that it exist (remain in scope) after you leave the loop).

Second, when you declare the bin array, you need to specify the size of the array.
float bin[] = new float[10]; // Creates an array of floats with 10 slots. b[0] - b[9] (You probably want the array to be the same size as the "data" array, so use data.length in place of "10")

Then in the loop you'd say
bin[j] = unbin;

Also, the way you are incrementing j (j = j+2), it looks like you wish to write to b[0] b[2] b[4], etc. You skip b[1], b[2], b[3]. If this is your intention, be sure you allocate enough room for the bin array. (I think you mean to do j = j+1);

answered Jun 14, 2012 at 13:40

ShWebb

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Comments

DrUseful · Accepted Answer · 2012-06-14 13:40:17Z

1

Subsequent to Jon's answer, as well as defining the array outside of the loop, you only need to add 1 to J, but ensure that the condition is

while ((2*j) <= data.length) {
    ....
}

You're also going to get ArrayIndexOutOfBoundsExceptions thrown, because when j = data.length, 2*j = 2* data.length, which is bigger than your data array.

answered Jun 14, 2012 at 13:40

DrUseful

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