A problem from "import" statement

Question

When I was doing some test on "package" and "import" statement, I had a problem.
1 I compiled one class:
package com.sheng.population;
public class A {
     public static int sum (int k, int l) {
          return (k+l);
2 I tried to call the method 'sum' in A:
import com.sheng.population.*;
public class B {
     public static void main(String[] args){
          int i=9;
          int j=100;
          int k = A.sum(i, j);
          System.out.println(k);
Then I got the error message:
"B.java:7: cannot access A
bad class file: E:\newjava\analysis\LDmeasure\A.java
file does not contain class A"
Only after I changed the import statement to "import com.sheng.population.A;" , then it worked.
I just do not know why the '.*' does not work?
Thanks

Answer 1

Let's say your directory structure is "e:\newjava\com\sheng\population\A.class" and "e:\newjava\analysis\LDmeasure\A.java"
If your Classpath is .;e:\newjava and when you compile, your current directory is e:\newjava\analysis\LDmeasure then you have A.java and A.class in your Classpath. When you use "import com.sheng.population.*;" the compiler does not know you mean com.sheng.population.A. The compiler finds A.java and thinks it is the A class that the B class needs. When it tries to compile A.java it finds the class name is com.sheng.population.A which causes the error. When you use "import com.sheng.population.A;" the compiler does not try to use A.java.
If you are keeping the source code in a different directory from the compiled classes, then you should not have the source code in the Classpath. So, if you make sure the current directory is not e:\newjava\analysis\LDmeasure then it should compile.