public class LoadingFromWhere {
  public static void main(String args[]){
    LoadingFromWhere s = new LoadingFromWhere();
    s.doit();
  }

  public void doit() {
    System.out.println(this.getClass().getName() + " is loaded from " +
      getClass().getProtectionDomain().getCodeSource().getLocation());

    MyClass s = new MyClass();
  }
}

class MyClass {
  MyClass() {
    System.out.println
     (this.getClass().getName() + " is loaded from " +
     this.getClass().getProtectionDomain().getCodeSource().getLocation());
  }
}

C:/temp>java LoadingFromWhere
LoadingFromWhere is loaded from file:/C:/temp/
MyClass is loaded from file:/C:/temp/

C:/temp>java -jar testing.jar
LoadingFromWhere is loaded from file:/C:/temp/testing.jar
MyClass is loaded from file:/C:/temp/testing.jar

package com.rgagnon;

public class FromWhere {
  public static void main(String args[]){
    Class theClass = FromWhere.class;
    java.net.URL u = theClass.getResource("");
    System.out.println("This class (FromWhere) is located at : " + u);
    }
}

C:/temp> java FromWhere
This class (FromWhere) is located at : file:/C:/temp/com/rgagnon