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Index › Programming Questions & Help › Syntax Questions › if ( value == null )
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if ( value == null ) (Read 1626 times)
Jon Cousins
if ( value == null )
Dec 2nd, 2009, 11:52am  
When I try to use...

Code:
if ( value == null )


...because processing won't allow me to set default argument variables for a function, I get this error:

Code:
The operator != is undefined for the argument type(s) float, null


I don't get it. 'value' is defined, and the whole idea of null is that it isn't defined either.

Can anyone help?
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« Last Edit: Dec 2nd, 2009, 12:57pm by Jon Cousins »  
 
koogy
Re: if ( value == null )
Reply #1 - Dec 2nd, 2009, 12:17pm  
only Classes can be null, and float is not a Class, it's a primitive type.
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liudr
Re: if ( value == null )
Reply #2 - Dec 2nd, 2009, 12:41pm  
Under what condition do you expect to see that your value is null? koogy is right, floats can't be null. null refers to a pointer pointing nowhere, instead of pointing to an object. Do you actually want to say if (value==0) instead? You should post more code.
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Jon Cousins
Re: if ( value == null )
Reply #3 - Dec 2nd, 2009, 12:55pm  
I wish to call a function which expect 2 values... but there are times when I don't want to pass any values and it to default to preset values.

In php I would do this...

Code:
void function(int x = 0, int y = 10)
{
  //code here
}


But it won't let me do this, so I thought I could just check if those values were null, like this...

Code:
void function(int x, int y)
{
  if ( x == null )
    x = 0;
  if ( y == null )
    y = 10;
}
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blindfish
Re: if ( value == null )
Reply #4 - Dec 2nd, 2009, 2:16pm  
This might be bad style (I'm not a Java programmer either); but you could perhaps use overloaded functions:

Code:
void setup() {
 size(100,100); 
  myFunction();
  myFunction(5,3);
}

void draw() {

  
}

void myFunction() {
  int x = 0;
  int y = 10;
  println(x + " " + y);
}

void myFunction(int x, int y) {
  println(x + " " + y);
}


If your function is going to be more complex then have the overloaded functions call a separate function passing the appropriate parameters...
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Where is the what if the what is in why?
 
PhiLho 
Re: if ( value == null )
Reply #5 - Dec 2nd, 2009, 2:33pm  
Quote:
This might be bad style

No, it is a very classical idiom in Java. Not the most elegant, but well, people do that routinely.
Eg. in Processing code itself:
Code:
  public void colorMode(int mode) {
    colorMode(mode, colorModeX, colorModeY, colorModeZ, colorModeA);
  }

  public void colorMode(int mode, float max) {
    colorMode(mode, max, max, max, max);
  }

  public void colorMode(int mode, float maxX, float maxY, float maxZ) {
    colorMode(mode, maxX, maxY, maxZ, colorModeA);
  }

  public void colorMode(int mode,
				float maxX, float maxY, float maxZ, float maxA) {
    // The complete code
  }
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koogy
Re: if ( value == null )
Reply #6 - Dec 3rd, 2009, 2:20am  
liudr wrote on Dec 2nd, 2009, 12:41pm:
Under what condition do you expect to see that your value is null koogy is right, floats can't be null. null refers to a pointer pointing nowhere, instead of pointing to an object. Do you actually want to say if (value==0) instead You should post more code.


i did nearly suggest this but couldn't think of a decent value to suggest as a default - 0 is quite commonly a useful value for things 8)

there's also the problem of comparisons with floats as sometimes what you ask for and what you get are two different things because a float can't store the exact value.

the lack of defaultable parameters in java is one of my (many) bugbears.
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PhiLho 
Re: if ( value == null )
Reply #7 - Dec 3rd, 2009, 2:45am  
Jon Cousins wrote on Dec 2nd, 2009, 12:55pm:
I thought I could just check if those values were null, like this...

Code:
void function(int x, int y)
{
  if ( x == null )
    x = 0;
  if ( y == null )
    y = 10;
}

Note 1: You can do that with void function(Integer x, Integer y), ie. encapsulating the int values in an object which then can hold the information "no data". It introduces a little overhead thought.
Note 2: Even if you do the above, it won't allow you to call function without parameters or with one parameter, Java compiler just won't allow that...
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liudr
Re: if ( value == null )
Reply #8 - Dec 3rd, 2009, 7:20am  
blindfish wrote on Dec 2nd, 2009, 2:16pm:
This might be bad style (I'm not a Java programmer either); but you could perhaps use overloaded functions:

Code:
void setup() {
 size(100,100); 
  myFunction();
  myFunction(5,3);
}

void draw() {

  
}

void myFunction() {
  int x = 0;
  int y = 10;
  println(x + " " + y);
}

void myFunction(int x, int y) {
  println(x + " " + y);
}


If your function is going to be more complex then have the overloaded functions call a separate function passing the appropriate parameters...


I would use this method as well. It increases a bit of overhead (double the code for two versions of a function, runtime overload may cost extra time). On the other hand, why not always supply the values even if the values are the default values? I use compile-time overload like above but you may get away by defining a macro (does java have macros or #define?) that replaces myFunction() with myFunction (default1, default2) at compile time. Like #define myFunction() myFunction (default1, default2);
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antiplastik
Re: if ( value == null )
Reply #9 - Dec 3rd, 2009, 7:35am  
No, duplicate code is terrible and you don't want that.

You would better go this way :

Code:
void myFunction(int x, int y) {
  println(x + " " + y);
}

void myFunction() {
  myFunction(0, 0);
}
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blindfish
Re: if ( value == null )
Reply #10 - Dec 3rd, 2009, 9:35am  
antiplastik wrote on Dec 3rd, 2009, 7:35am:
No, duplicate code is terrible and you don't want that.

You would better go this way :

Code:
void myFunction(int x, int y) {
  println(x + " " + y);
}

void myFunction() {
  myFunction(0, 0);
}


That's a nice succinct way of handling it!  I certainly wasn't suggesting duplicating code - I was thinking more along the lines of:

Code:
void myFunction() {
  int x = 0;
  int y = 10;
  myComplexFunction(x,y);
}

void myFunction(int x, int y) {
  myComplexFunction(x,y);
} 

void myComplexFunction(int x, int y) {
  // does stuff
}


...But of course if I'd actually typed that out I would have quickly realised that it was a little clunky and would have resorted to your approach (honest!)  Grin
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Where is the what if the what is in why?
 
PhiLho 
Re: if ( value == null )
Reply #11 - Dec 3rd, 2009, 9:46am  
Quote:
(does java have macros or #define?)

No.
Java programmers use overloading and polymorphism instead... :)
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« Last Edit: Dec 3rd, 2009, 11:36am by PhiLho  »  
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antiplastik
Re: if ( value == null )
Reply #12 - Dec 3rd, 2009, 9:50am  
liudr wrote on Dec 3rd, 2009, 7:20am:
I would use this method as well. It increases a bit of overhead (double the code for two versions of a function, runtime overload may cost extra time).


@blindfish : I was punching liudr in the face, not you... but, mmm.. right, you wrote the code so you deserve your punch too ;-)   no hard feelings :-)
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