string==null or string.equals(null) problem

Error corrected. I need to add:

Code :

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str4 = null;

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in order to "clear out" what was in it whenever it looped.

Glad you figured it out, Due to giving answers out I'm not allowed to post code :(

But congratulations on figuring it out.

Quote:

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Originally Posted by macko

Well, Anything can be simplified... If your doing the same thing in a loop more then 4 times you should be able to narrow it down, as for the null of a string..

Code :

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if(string.equals("")){
 
}

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That does not test whether a Sting is null. In fact, that will result in an NPE if the String is null.

Quote:

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Originally Posted by macko

Glad you figured it out, Due to giving answers out I'm not allowed to post code :(

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It's not that you aren't allowed to post code, it's just that posting full code solutions (especially when your solutions aren't completely correct, like the code you posted in this thread that actually causes Exceptions) isn't actually helpful. Again, I'm not trying to be a jerk, and I understand how fun it can be to solve problems, but it's a lot of work for us moderators to keep track of people who are giving out bad advice.

Say you declare a string

public String str = "";

it will not return as null during the program..

you're simply searching for a blank string.

Its only if you were to declare it at the top like

public String str;

that would display null as you are not initializing any values to it..

So no im not checking if the string is null, Im checking if the string contains anything...

Well, OP must know the difference between == and equals(). So,

== actually tells you if the two object references are refering to the same instance, i.e.

Code :

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String x="Hello"
String y=x;
x==y;

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Here the result will be true as both are referencing the same instance.

But,

Code :

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String x="Hello";
String y=new String ("Hello");
x==y;

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here the result will be false because both are referring to the different instances.


Now come to the equals(). Actually equals() compare the character values of a String object.

Code :

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String x="Hello";
String y="Hello";
x.equals(y); //True
String z=new String(y);
x.equals(z);//true
But x==z; //False

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Hope this will help you alot, understanding the concept.
Thanks

Quote:

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Originally Posted by macko

Say you declare a string

public String str = "";

it will not return as null during the program..

you're simply searching for a blank string.

Its only if you were to declare it at the top like

public String str;

that would display null as you are not initializing any values to it..

So no im not checking if the string is null, Im checking if the string contains anything...

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Right, but that isn't what the OP was asking, and it's not what you advertised it as (your original post said it was checking the null of the String). Again, in the OP's case, your suggestion would actually cause an Exception to be thrown.