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Showing messages 1 through 14 of 14.
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good article
2008-09-04 06:01:08 units [Reply | View]
Youtube
youtube
youtube, izlesene
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Old fashioned or...
2006-01-18 05:42:52 pholthuizen [Reply | View]
Personally I like the ? operator in string concatenations. The others I never use so you may strip them from the language if you please...
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power
2006-01-17 14:13:06 sirian98 [Reply | View]
Just look at this code I wrote before I found about bitwise operators in java, because of this article; thanks!
Here I am trying to break a byte that I read from a file into four tertiary numbers:
public static final int[] bite(int inByte)
{
int[] bites = new int[4];
int tooth = 0;
int remainder = inByte;
for(int i = 0; i < 4; i++)
{
bites[i] = remainder / (int)(Math.pow(4,3-i));
remainder = remainder % (int)(Math.pow(4,3-i));
}
return bites;
}
now bitwise:
Just look at this code I wrote before I found about bitwise operators in java, because of this article; thanks!
Here I am trying to break a byte that I read from a file into four tertiary numbers:
public static final int[] bite(int inByte)
{
int[] bites = new int[4];
for(int i = 0; i < 4; i++)
{
bites[i] = inByte%4;
inByte = inByte >>2;
}
return bites;
}
modulus + bitwise = power -
Crumb twiddling
2006-01-18 03:53:55 tackline [Reply | View]
That code doesn't do quite what it appears to. If
inByteis negative, then the elements of the returned array will all be non-positive. Perhaps the method should only be called with values between 0 and 255 inclusive, in which case it should throw anIllegalArgumentExceptionfor exceptional cases when it is passed an illegal argument.The problem is that both
%and>>are signed operators. The semantics of%(and integer division) are rather arbitrary, so check the Java Language Spec (JLS) for the tedious details. Replacing either by unsigned equivalent operations would do. As 4 is a power of two,x%4can be replaced with the bitwise expressionx & 3, giving a non-negative result.x >> 2can be replaced using the logical (rather than arithmetic) right shift operator,x >>> 2. The intent is more obvious if both expressions are replaced.For code like this I would tend to write it as:
public static final int[] byteToLittleEndianCrumbs(int byteValue) {
if (!(0 <= byteValue && byteValue <= 0x100)) {
throw new IllegalArgumentException();
}
return new int[] {
(byteValue >> 0) & 0xf,
(byteValue >> 2) & 0xf,
(byteValue >> 4) & 0xf,
(byteValue >> 6) & 0xf,
}
}It is repetive, but in this case clearer than the loop.
Since Java 1.5, Integer and Long have gained a number of bit twiddling methods, along similar lines to these bitwise operators. IMO, the library would have been a better place for them all.
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a better way...
2006-01-17 11:53:34 karakfa [Reply | View]
the last example is just self negating. A better way of writing it is without the "?:" operator.
int a = -10;
boolean isNegative = a<0; // or put parathesis around
System.out.println(inNegative);
However, there are many valid cases...
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Operators
2006-01-17 06:31:49 heaththegreat [Reply | View]
From:
http://java.sun.com/docs/books/tutorial/java/nutsandbolts/bitwise.html
op1 << op2
Shifts bits of op1 left by distance op2; fills with 0 bits on the right side
op1 >> op2
Shifts bits of op1 right by distance op2; fills with highest (sign) bit on the left side
op1 >>> op2 Shifts bits of op1 right by distance op2; fills with 0 bits on the left side
From:
http://java.sun.com/docs/books/tutorial/java/nutsandbolts/other.html
op1 ? op2 : op3
If op1 is true, returns op2; otherwise, returns op3
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Well they are quite intuitive i think...
2006-01-17 05:53:22 wfvoogd [Reply | View]
Let's start with the easy one; the question mark and colon (? :)
That a shorthand for the if statement. sometimes you just want to assign a certain value under a certain condition.
ie.
int a = 0; boolean negativeValue; if (a>=0) negativeValue = false; else negativeValue = true;you could write that as:
int a = 0; boolean negativeValue = (a>=0)?false:true;
So it's just a shorthand if..else really.
Hope this helps,
Willem -
Otherwise known as a ternary operator
2006-01-17 13:49:46 phuego [Reply | View]
The ? and : chars are correctly known when used together as a 'ternary operator'.
I find them particularly useful for refactoring a block of code that does this, or that, based on a boolean.
For example you have a method that filters a List. The way the List is filtered depends on a GUI setting, for arguments sake 'include zero'.
So you might code like this:public List filterListOfIntegersToPositives(List original, boolean inclZero) { List ret = new ArrayList(original.size()); if (inclZero) { // code that does filtering for(int i=0; i<original.size(); i++){ Integer thisInt = originals.get(i); if (thisInt.compareTo(Integer.valueOf(0)) > -1) { ret.add(thisInt); } } // end code that does filtering } else { // code that does filtering for(int i=0; i<original.size(); i++){ Integer thisInt = originals.get(i); if (thisInt.compareTo(Integer.valueOf(0)) > 0) { ret.add(thisInt); } } // end code that does filtering } return ret; }
Now you look at that code, and you think to yourself - the code that does filtering (as commented) is duplicated, and that violates "Don't repeat Yourself" and so I need to refactor that to a better design. good thought.
So we look and we see that the only part that changes in the duplicated code is the value of the int we compare to (it changes from -1, to 0)
So, using a ternary operator, we could refactor that method as follows:
public List filterListOfIntegersToPositives(List original, boolean inclZero) { List ret = new ArrayList(original.size()); for(int i=0; i<original.size(); i++){ Integer thisInt = originals.get(i); if (thisInt.compareTo(Integer.valueOf(0)) > (inclZero? -1 : 0)) { ret.add(thisInt); } } return ret; }
Much cleaner.
Now, i have to admit, I've never used bitshifting either! So I'm looking forward to the "why you'd actually do this" post on that. Hope that helps to clarify ternary operators and why you'd use them just a little.
Adrian -
Otherwise known as a ternary operator
2006-01-17 14:11:25 sirian98 [Reply | View]
Just look at this code I wrote before I found about bitwise operators in java, because of this article; thanks!
Here I am trying to break a byte that I read from a file into four tertiary numbers:
public static final int[] bite(int inByte)
{
int[] bites = new int[4];
int tooth = 0;
int remainder = inByte;
for(int i = 0; i < 4; i++)
{
bites[i] = remainder / (int)(Math.pow(4,3-i));
remainder = remainder % (int)(Math.pow(4,3-i));
}
return bites;
}
now bitwise:
Just look at this code I wrote before I found about bitwise operators in java, because of this article; thanks!
Here I am trying to break a byte that I read from a file into four tertiary numbers:
public static final int[] bite(int inByte)
{
int[] bites = new int[4];
for(int i = 0; i < 4; i++)
{
bites[i] = inByte%4;
inByte = inByte >>2;
}
return bites;
}
modulus + bitwise = power -
[Reposted] Otherwise known as a ternary operator
2006-01-17 13:56:54 phuego [Reply | View]
So sorry, completely forgot about formatting.
Here is the 'before' code from my first post.public List filterListOfIntegersToPositives(List original, boolean inclZero) { List ret = new ArrayList(original.size()); if (inclZero) { // code that does filtering for(int i=0; i<original.size(); i++){ Integer thisInt = (Integer) original.get(i); if (thisInt.compareTo(Integer.valueOf("0")) > -1) { ret.add(thisInt); } } // end code that does filtering } else { // code that does filtering for(int i=0; i<original.size(); i++){ Integer thisInt = (Integer) original.get(i); if (thisInt.compareTo(Integer.valueOf("0")) > 0) { ret.add(thisInt); } } // end code that does filtering } return ret; }
And here is the code after you've refactored using a ternary operator...
public List filterListOfIntegersToPositives(List original, boolean inclZero) { List ret = new ArrayList(original.size()); // code that does filtering for(int i=0; i<original.size(); i++){ Integer thisInt = (Integer) original.get(i); if (thisInt.compareTo(Integer.valueOf("0")) > (inclZero ? -1 : 0)) { ret.add(thisInt); } } // end code that does filtering return ret; }
Apologies for the mistake before - why is there no Preview post in this forum???
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