What is the correct way to declare a boolean variable in Java

Question

I have just started learning Java  In the online course I am following  I am asked to try the following code   String email1    meme me coh   String email2    meme me com   Boolean isMatch   false   isMatch   email1 equals  email2    if  isMatch    true       System out println  Emails match      else      System out println  Emails don t match        I don t understand why I m asked to declare isMatch as false when on the next line i am comparing the email addresses and assigning the value to isMatch  I ve tried the following code which seems to work just the same   String email1    meme me coh   String email2    meme me com   Boolean isMatch   isMatch   email1 equals  email2    if  isMatch    true       System out println  Emails match      else      System out println  Emails don t match        On the course it doesn t explain why I m declaring isMatch as false first  Is there a reason why I must declare isMatch as false before comparing the email addresses

User · Accepted Answer

You don t have to  but some people like to explicitly initialize all variables  I do too   Especially those who program in a variety of languages  it s just easier to have the rule of always initializing your variables rather than deciding case-by-case language-by-language   For instance Java has default values for Boolean  int etc    C on the other hand doesn t automatically give initial values  whatever happens to be in memory is what you end up with unless you assign a value explicitly yourself   In your case above  as you discovered  the code works just as well without the initialization  esp since the variable is set in the next line which makes it appear particularly redundant  Sometimes you can combine both of those lines  declaration and initialization - as shown in some of the other posts  and get the best of both approaches  i e   initialize the your variable with the result of the email1 equals  email2   operation

User · Answer

Not only there is no need to declare it as false first  I would add few other improvements    use boolean instead of Boolean  which can also be null for no reason  assign during declaration   boolean isMatch   email1 equals email2       and use final keyword if you can   final boolean isMatch   email1 equals email2      Last but not least   if  isMatch    true    can be expressed as   if  isMatch    which renders the isMatch flag not that useful  inlining it might not hurt readability  I suggest looking for some better courses tutorials out there

User · Answer

First of all  you should use none of them  You are using wrapper type  which should rarely be used in case you have a primitive type  So  you should use boolean rather   Further  we initialize the boolean variable to false to hold an initial default value which is false  In case you have declared it as instance variable  it will automatically be initialized to false   But  its completely upto you  whether you assign a default value or not  I rather prefer to initialize them at the time of declaration   But if you are immediately assigning to your variable  then you can directly assign a value to it  without having to define a default value   So  in your case I would use it like this  -  boolean isMatch   email1 equals  email2

User · Answer

As stated by Levon  this is not mandatory as stated in the docs  http   docs oracle com javase tutorial java nutsandbolts datatypes html  This is probably either an habit from other languages that don t guarantee primitive data types default values

User · Answer

In your example  You don t need to  As a standard programming practice  all variables being referred to inside some code block  say for example try   catch      and being referred to outside the block as well  you need to declare the variables outside the try block first e g   This is helpful when your equals method call throws some exception e g  NullPointerException        boolean isMatch   false        try           isMatch   email1 equals  email2          catch NullPointerException npe                                System out print  Match    isMatch         if isMatch

User · Answer

There is no reason to do that  In fact  I would choose to combine declaration and initialization as in  final Boolean isMatch   email1 equals  email2     using the final keyword so you can t change it  accidentally  afterwards anymore either

[java] What is the correct way to declare a boolean variable in Java?

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