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

  1. #26
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    Default Re: string==null or string.equals(null) problem

    Error corrected. I need to add:

    str4 = null;

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

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    Default Re: string==null or string.equals(null) problem

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

    But congratulations on figuring it out.

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    Default Re: string==null or string.equals(null) problem

    Quote Originally Posted by macko View Post
    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..

    if(string.equals("")){
     
    }
    That does not test whether a Sting is null. In fact, that will result in an NPE if the String is null.
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    Default Re: string==null or string.equals(null) problem

    Quote Originally Posted by macko View Post
    Glad you figured it out, Due to giving answers out I'm not allowed to post code
    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.
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    Default Re: string==null or string.equals(null) problem

    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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    Default Re: string==null or string.equals(null) problem

    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.
    String x="Hello"
    String y=x;
    x==y;
    Here the result will be true as both are referencing the same instance.

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

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

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    Default Re: string==null or string.equals(null) problem

    Quote Originally Posted by macko View Post
    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...
    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.
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