what is static import

[ankur rathi]

can any body explain me what is static import . If possible can provide code ...

thanks a lot .

[Jeff Bosch]

Java 1.5 Static Import.

[ankur rathi]

I never though that it would be such a simple thing .

class My {
System.out.println(Math.PI);
}

static import java.lang.Math;
class My {
System.out.println(PI);
}

both code are doing same thing , but in second case all the variable ( PI & E ) are being created locally for My class or in other word , we have a local copy of all the variable in My class .

Is this right ... and sufficient for beta ....

thanks a lot .
[ February 02, 2005: Message edited by: rathi ji ]

[Joyce Lee]

There're few flaws in the code:
1. It should be import static
2. To import a static member like PI in Math, it should be

import static java.lang.Math.PI;

or

import static java.lang.Math.*;// using wildcard

So be careful, don't get mixed up with normal import.

[ankur rathi]

It means , If we are importing a class then we will use * sign & If we are importing particular member ( variable only , method is not possible I think ) then we will not use * sign .

Is this right ?

Please reply .

Thanks a lot .

[ankur rathi]

one more thing Joyce , Why you wrote wildcard in this ...

import static java.lang.Math.*;// using wildcard

thanks .

[Joyce Lee]

Wildcard allows importing all the static members of Math class in one statement. Let's say, you want to import some static members like PI, min and max in Math, there are two approaches to do this:

  
import static java.lang.Math.PI;
import static java.lang.Math.max;
import static java.lang.Math.min;

or simply

import static java.lang.Math.*;

[amit taneja]

Hi rathi ji

i have sent u private message ..kindly reply it...


amit

[ankur rathi]

I have replied !!!

[ankur rathi]

Thanks Joycee ....

Is it possible to import static method() also .... I think not .. but please reply ..

thanks a lot ...

[Joyce Lee]

Is it possible to import static method() also .... I think not .. but please reply ..

Yes, it's possible. max and min are static methods in Math class. You can also import a static nested class.

Here is an example:

Filename: StaticClass.java

package my.com;
 
public class StaticClass {
    public static int i = 1;
    
    public static int getValue() {
        return 2;
    }
 
    public static class Inner {
        public int getOtherValue() {
            return 3;  
        }    
    }
}

Filename: TestStatic.java

import static my.com.StaticClass.i;
import static my.com.StaticClass.getValue;
import static my.com.StaticClass.Inner;
 
public class TestStatic {
    public static void main(String[] args) {
        System.out.println(i);
        System.out.println(getValue());
        System.out.println(new Inner().getOtherValue());
    }
}

Try compile the code and see the result.

[Joyce Lee]

Another example using generic:

Filename: Outer2.java

package my.com;
 
public class Outer2<T> {
    public static class Inner<T> {
        public static <T> void method1(T o) {
            System.out.println(o);
        }            
        
        public void method2(T o) {
            System.out.println(o);
        }
    }
}

Filename: TestOuter.java

import static my.com.Outer2.Inner;
import static my.com.Outer2.Inner.method1;
 
public class TestOuter {
    public static void main(String[] args) {
        Inner<String> in = new Inner<String>();
        in.method2("Hello");
        method1(new Thread("There"));
    }
}

[ankur rathi]

Inner<String> in = new Inner<String>();

Joycee , How can you create an instance on static inner class without specifying outer class name .
I think the correct code should be this :

Outer.Inner<Integer> in = new Outer.Inner<Integer>();

please reply ...

thanks .