Static import in Java allows importing static members of the class and use
them, as they are declared in the same class. Static import is introduced in
Java 5 along with other features like Generics,
Enum,
Autoboxing
and Unboxing and variable
argument methods. Many programmers think that using static import can reduce
code size and allow you to freely use static field of external class
without prefixing class name on that. For example, without static import, you will
access static constant MAX_VALUE of Integer class as Integer.MAX_VALUE but by
using static import you can import Integer.MAX_VALUE and refer
it is MAX_VALUE.
Similar to regular import statements, static import also allows wildcard * to import all static members of a class. In the next section, we will see the Java program to demonstrate How to use static import statements to import static fields.
Similar to regular import statements, static import also allows wildcard * to import all static members of a class. In the next section, we will see the Java program to demonstrate How to use static import statements to import static fields.
Static import example in Java
In this static import example, we have imported constants Integer.MAX_VALUE and Integer.MIN_VALUE statically
and printing their value without prefixing class
name on that.
package test;
import static java.lang.Integer.MAX_VALUE;
import static java.lang.Integer.MIN_VALUE;
/**
*
* Java program to demonstrate How to use static import in Java 5
* By using static import you can use static field of external class
* as they are declared in the same class.
*
* @author Javin Paul
*/
public class StaticImportExample {
public static void main(String args[]) {
//without Static import
System.out.println("Maximum value of int variable in Java without " +
import static java.lang.Integer.MAX_VALUE;
import static java.lang.Integer.MIN_VALUE;
/**
*
* Java program to demonstrate How to use static import in Java 5
* By using static import you can use static field of external class
* as they are declared in the same class.
*
* @author Javin Paul
*/
public class StaticImportExample {
public static void main(String args[]) {
//without Static import
System.out.println("Maximum value of int variable in Java without " +
"static import
: " + Integer.MAX_VALUE);
System.out.println("Minimum value of int variable in Java without " +
System.out.println("Minimum value of int variable in Java without " +
static import :
" + Integer.MIN_VALUE);
//after static import in Java 5
System.out.println("Maximum value of int variable using " +
//after static import in Java 5
System.out.println("Maximum value of int variable using " +
static import :
" +
MAX_VALUE);
System.out.println("Minimum value of int variable using" +
System.out.println("Minimum value of int variable using" +
static import : " + MIN_VALUE);
}
}
Output:
Maximum value of int variable in Java without static import : 2147483647
Minimum value of int variable in Java without static import : -2147483648
Maximum value of int variable using static import : 2147483647
Minimum value of int variable using static import : -2147483648
}
}
Output:
Maximum value of int variable in Java without static import : 2147483647
Minimum value of int variable in Java without static import : -2147483648
Maximum value of int variable using static import : 2147483647
Minimum value of int variable using static import : -2147483648
If you look at import statements import static java.lang.Integer.MAX_VALUE, its
written as import static rather than static import, so just
beware of that. We are not using * wildcard
here and importing only selected static members but you can also use import
static java.lang.Integer.* to import
all static
fields in one go.
Advantages of Static Import in Java
The main advantage of using static
import in Java is saving keystrokes. If you are frequently using System.out.println() statements
and tried of typing it, you can statically import System.out or System.* and subsequently
you can type out.println() in your code, Though I would
suggest using this Eclipse
shortcut to generate System.out.println statement which is much faster than
static import.
This is the kind of usage I see one can benefit from static import, other than that static import is just an extension of regular import statement in Java. Similar to the static field you can also import static methods in your class, mostly in the case of Utility classes.
This is the kind of usage I see one can benefit from static import, other than that static import is just an extension of regular import statement in Java. Similar to the static field you can also import static methods in your class, mostly in the case of Utility classes.
The drawback of Static Import in Java
Many Java programmers argue against static import with a reason that it reduces readability and goes against how static field
should be used i.e. prefixed with class name e.g. Integer.MAX_VALUE.
Static import has another drawback in terms of conflicts, once you static import Integer.MAX_VALUE you can not use MAX_VALUE as variable in your programmer, the compiler will throw an error.
Similarly if you static import both Integer.MAX_VALUE and Long.MAX_VALUE and refer them in code as MAX_VALUE, you will get the following compile time error :
Static import has another drawback in terms of conflicts, once you static import Integer.MAX_VALUE you can not use MAX_VALUE as variable in your programmer, the compiler will throw an error.
Similarly if you static import both Integer.MAX_VALUE and Long.MAX_VALUE and refer them in code as MAX_VALUE, you will get the following compile time error :
java.lang.ExceptionInInitializerError
Caused by: java.lang.RuntimeException: Uncompilable source code -
MAX_VALUE is already defined in a static single-type import
at test.StaticImportExample.(StaticImportExample.java:6)
Could not find the main class: test.StaticImportExample. Program will exit.
Exception in thread "main" Java Re
Summary
Finally few points worth remembering about static import in Java :
1) Static import statements are written as "import
static" in code and not "static import".
2) If you import two static fields with the same name explicitly e.g. Integer.MAX_VALUE and Long.MAX_VALUE then Java
will throw compile-time error. But if another static modifier is not imported
explicitly e.g. you have imported java.lang.Long.*, MAX_VALUE will refer
to Integer.MAX_VALUE.
3) Static import doesn't improve readability as expected, as many Java programmers prefer Integer.MAX_VALUE which is clear that which MAX_VALUE are you
referring.
4) You can apply static import statement not only
on static fields but also on static methods in Java.
That's all on What is static import in Java 5, What is the advantages
and drawbacks of using static import in Java program, and how to use static
import in Java. Honestly, it's been almost a decade since Java 5 was released but I
have rarely used static import statements. Maybe in the future, I may
figure out a strong convincing reason to use static import
Other Java 5 tutorial from Javarevisited
Similar to Python. Even I am not in favor as it reduces code readability
ReplyDeleteLogical and best use of static import in Java is visible in Testing framework e.g. JUnit, TestNG and Spring testframework which supports annotation. static importing all Assert methods in Junit e.g. org.junit.Assert.* and using them like asssertEquals() seems perfectly fine to me than Asert.assertEquals(). So if you name properly you can still use static import effectively in Java.
ReplyDeleteI was receiving error You can only import static from classes and interfaces, while import @Test annotation for writing JUnit test, please help
ReplyDeleteOne of the better use of Java static import, I have seen in recent year is for importing constants. Earlier developer used to use interface to declare constant and later get access to them, by implementing interface, which not only obscure constants in inheritance hierarchy but also defeats whole purpose of using interface for abstraction. By using static import, you can easily find which constant, comes from where, means better readability.
ReplyDeleteHello, I am trying to import static constant as below, but its giving me compile time error saying "Only a type can be imported, java.nio.file resolves to a package"
ReplyDeleteimport static java.nio.file.*
Can't we import static constants from a package in Java?
@Anonymous, No, only static members from a class can be imported using "import static" statements, that includes static fields and static methods. Right way to use static import in your case would be
ReplyDeleteimport static java.nio.file.Files.*
I have static import feature a lot while using unit testing and mocking libraries like Mockito, JUnit, TestNG and others. You can static import key class e.g.
ReplyDeleteimport static org.junit.Assert.*
import static org.mockito.Mockito.*
import static org.mockito.Matcher.*
You can even configure Eclipse content assist to show statically imported method, without even them manually imported, by configuring them in favorites under content assist. Next time, if those libraries in your classpath, typing assert will show all assert methods from jUnit and so on.
i didnt understand the drawback as i can use max_value as a variable once i static import Integer.MAX_VALUE ,it is not giving compilation error
ReplyDeleteThe main reason why static import was introduced in java was to avoid Constant Interface Anti Pattern.
ReplyDeleteGoogle more for Constant Interface antipattern and how static import overcomes it.
I use 'import static' for importing constant values which are stored in a class, i.e I store properties of database like username, password, url in a class and later I use them by their name instead of classname.username
ReplyDelete