With respect to accessing static content, difference between custom package and java system package

[karunakar theru]

Q) With respect to accessing static content, what is the difference between user defined package and java system package (say java.lang etc)  I'm preparing for ocjp6. using 1.6.26 java version
my java program has a package named "pack" in PackageTest.java

    package pack;
    public class PackageTest {
	    public static final int i=20;
      }
    }

javac -d . PackageTest.java
created PackageTest.class file in pack folder
now accessing static contents of PackageTest class from another java
program (TestStaticContents.java) as below

    import pack.PackageTest.*; 
    // here importing all contents of PackageTest class
    class TestStaticContents {
    public static void main(String[] args){
    System.out.println("normal import, accessing i value with class name: "+PackageTest.i);
        }
    }

javac TestStaticContent.java  
displaying Compilation Error:
TestStaticContents.java: cannot access PackageTest bad class file: .\PackageTest.java

If i try accessing static contents of Math class from my java program
its not displaying any compilation error i.e

    import java.lang.Math.*; 
    // here importing all contents of Math class
    class TestMathStaticContents {
    public static void main(String[] args){
    System.out.println("normal import, accessing pi value with class name : "+ Math.PI);
        }
    }

javac TestMathStaticContents.java
No Compilation Error, and PI value
is printed as expected
-------------------
Why this behavior is different compared to User defined package

[Paul Anilprem]

Try moving your PackageTest.java file away from the directory in which you have TestStaticContents.java while compiling TestStaticContents.java.
Or compile both the files together using -d  . option.
javac -d . *.java

[Roel De Nijs]

karunakar theru wrote:Why this behavior is different compared to User defined package

That's very simple: classes from the java.lang package are imported by default. Although the import you are using is wrong to import the Math class, it still works because you simply don't need to add imports for classes in the java.lang package. So this class will compile and run successfully too

class TestMathStaticContents {
    public static void main(String[] args) {
        System.out.println("normal import, accessing pi value with class name : " + Math.PI);
    }
}

But this only applies to classes in the java.lang package, not to user-defined packages nor to other packages from the JDK.

karunakar theru wrote:javac TestStaticContent.java
displaying Compilation Error:
TestStaticContents.java: cannot access PackageTest bad class file: .\PackageTest.java

In this topic and this one provide an excellent explanation about how to compile Java source code files in different folders using a similar example. I'm pretty sure after carefully reading this topic all your doubts (concerning this topic) will be cleared. If you still have doubts/questions after reading these topics, simply click on the "Post reply" button and let us know

Hope it helps!
Kind regards,
Roel

[karunakar theru]

Very useful explanation. Thank you very much Roel.