First lets understand what does “java import” does to your java program!
Consider the java import statements:
1) import package.ClassA;
2) import package.*;
Java statement (1) gives you a license to use ClassA inside the whole program without the package reference. That is you can use like ClassA obj = new ClassA(); or ClassA.getStatic(); Java statement (2) allows you to use all the java classes that belong the imported package in the above manner. That is without the package reference.
If you don’t use import statement, you can still use the classes of that package. But you should invoke it with package reference whereever you use.
That is like, package.ClassA obj = new package.ClassA(); – looks very ugly isn’t it?
Now coming to the static import part. Like the above ugly line we have been unknowingly using (abusing) the java static feature.
Consider the java example: double r = Math.cos(Math.PI * theta);
How about writing the same java code like: double r = cos(PI * theta); – looks more readable right?
This is where static import in java comes to help you.
import static java.lang.Math.PI;
import static java.lang.Math.cos;
Do the above static imports and then you can write it in the more readable way!
The normal import declaration imports classes from packages, so that they can be used without package reference. Similarly the static import declaration imports static members from classes and allowing them to be used without class reference.
Now, we have got an excellent java feature from java 1.5. Ok now we shall see how we can abuse this!
like, import static java.lang.Math.*; – yes it is allowed! Similarly you do for class import.
Please don’t use this feature, because over a period you may not understand which static method or static attribute belongs to which class inside the java program. The program may become unreadable.
General guidelines to use static java import:
1) Use it to declare local copies of java constants
2) When you require frequent access to static members from one or two java classes
This Core Java tutorial was added on 14/06/2008.