checking if an object is null

[sprightee]

Hi,
I've a simple object class as testObj.java with getter and setter methods.
In my code i need to check if the testObj object is null.

My code is :
testObj test = new testObj();
//invoke a method A which returns test as return type
if(test==null || test.equals("") )
{
System.out.prin tln("The test object is null);
}

But i'm not getting the expected results. How to check if this test object is null?

[DeMan]

try using .equals

if(this.equals(null))
{
doThings
}

[DeMan]

As an aside in this vein....

== compares something (someone will hopefully explain exactly what)

.equals is a method provided by ALL objects (which you overide by defining your own equals methof).

So then,
if you have a method called myString.

You can define equals to do anything (as long as it takes an object as input and returns a boolean)

i had mopre to say but I forgot, so post more if you want more information or this doesn't quite make sense....

[r035198x]

Hi,
I've a simple object class as testObj.java with getter and setter methods.
In my code i need to check if the testObj object is null.

My code is :
testObj test = new testObj();
//invoke a method A which returns test as return type
if(test==null || test.equals("") )
{
System.out.prin tln("The test object is null);
}

But i'm not getting the expected results. How to check if this test object is null?

When you get an object using the new keyword and thus calling the constructor, you will never get that object as null. i.e Constructors never return null objects.

To test if an object is null you simply use

if(object == null) {

[r035198x]

try using .equals

if(this.equals(null))
{
doThings
}

This won't work. If an object is null, calling .equals or any method on it will give a NullPointerExce ption

[DeMan]

I see what you mean ( i made the mistake of assuming that we were testing something against null, but you're right, if it's true, then the test doesn't work because it doesn't refer to the type whose equals we use <I know what I meant>, I didn't even think of that......)

[sprightee]

When you get an object using the new keyword and thus calling the constructor, you will never get that object as null. i.e Constructors never return null objects.

To test if an object is null you simply use

if(object == null) {

sorry i'm not using the constructor.
My code is inside the method A which i'm calling is :

testObj test = null;
//Invoke this method
search(String str)

return test ;

When the search doesnot match any case, then it returns the tes obj as null.

So in may main program how can i check if the testObj is null.
I use
if(test==null || test.equlas("")

But this does not work

[r035198x]

sorry i'm not using the constructor.
My code is inside the method A which i'm calling is :

testObj test = null;
//Invoke this method
search(String str)

return test ;

When the search doesnot match any case, then it returns the tes obj as null.

So in may main program how can i check if the testObj is null.
I use
if(test==null || test.equlas("")

But this does not work

Just use

 if(test == null) {

What do you mean by "this does not work"? What results are you getting and what are you expecting to get?

[sprightee]

Just use

 if(test == null) {

What do you mean by "this does not work"? What results are you getting and what are you expecting to get?

if(test==null)
{
System.out.prin tln("The object is null);
}
else
{
System.out.prin tln("Not null");
}

OUTPUT:
Not null

[r035198x]

if(test==null)
{
System.out.prin tln("The object is null);
}
else
{
System.out.prin tln("Not null");
}

OUTPUT:
Not null

That my friend is actually because test is Not null.
What makes you think that it's supposed to be null at that stage?

[sprightee]

That my friend is actually because test is Not null.
What makes you think that it's supposed to be null at that stage?

Because this object is basically a VO object and is filled based on the search done in database and filled by the values fetched from the database and returned to the main program.
As i'm searching for a string that does not match any records in the database then it shud return a testObj which is null.

[r035198x]

Because this object is basically a VO object and is filled based on the search done in database and filled by the values fetched from the database and returned to the main program.
As i'm searching for a string that does not match any records in the database then it shud return a testObj which is null.

Well the values are being found! You can print the value of the object if it has a good toString on it to see the value. Check your search logic again.

[vivax83]

exercice = request.getParameter("exercice");

      try {
          if (exercice.equals(null)){
            out.println("IT IS REALLY NULL ...BUT THIS WILL NEVER BE PRINTED BECAUSE OF THE NullPointerException<br/>");
          }
      } catch (NullPointerException e) {
          out.println("I'M REALLY SURE exercice IS NULL ... <br/>");
      } catch (Exception e) {
          out.println("NOT REALLY SURE exercice IS NULL ... <br/>");
      }