Questions about string comparison

[Azuritul Wu]

Hello everyone:

While I was reading other people's code...I found the following two coding styles...And I am a little bit curious that whether they differ only in style or some other areas?

  String operation = (String)request.getAttribute("operation");
  
  //some code here
  
  if(operation.equals("doAdd")){
    //some operation
  }
  else if(operation.equals("doDelete")){
    //some operation
  }
  else if(operation.equals("doModify")){
   //some operation
  }

  public static final String DO_ADD = "doAdd";
  public static final String DO_DELETE = "doDelete";
  public static final String DO_MODIFY = "doModify";
  
  /*
   *  some code here
   */
 
  if(DO_ADD.equals(operation)){
      //do something
  }
  else if(DO_DELETE.equals(operation)){
      //do something
  }
  else if(DO_MODIFY.equals(operation)){
      //do something
  }
  else {
      //do something
  }

[Mani Ram]

In the first case, if the variable operation is null, you will get a NullPointerException, when the String is compared. But that won't be the case with the second style.

Additionaly, it is easy to change "doModify" to "doUpdate", if they are defined at a single place as given in the second approach.

[David Harkness]

The first method will get a null pointer exception if the request attribute isn't present. Other than that, the second is generally preferred as it's clearer and easier to change later.

[Azuritul Wu]

Thanks for the help.
Now i know how to use it.

Thank you.

[Ko Ko Naing]

The usage of Constants are pretty good, where there might be a need to change the actual value. As for the null value checking, I prefer checking the null value before doing actual operation on the variable. Otherwise, the unforgivable NullPointerException will occur.

[James Carman]

Originally posted by Ko Ko Naing:
The usage of Constants are pretty good, where there might be a need to change the actual value. As for the null value checking, I prefer checking the null value before doing actual operation on the variable. Otherwise, the unforgivable NullPointerException will occur.

The point is that with the constant.equals() trick, you don't have to worry about the NullPointerException, because it won't happen. You know the constant String is non-null and the String class can compare itself to a null value and return false.