单项选择题 What will be written to the standard output when the following program is run？（）   public class Q03e4 {   public static void main（String args[]） {   String space = " "；   String composite = space + "hello" + space + space；   composite.concat（"world"）；   String trimmed = composite.trim（）；   System.out.println（trimmed.length（））；   }   }

单项选择题 GiventhatfileisareferencetoaFileobjectthatrepresentsadirectory，whichcodefragmentswillsucceedinobtainingalistoftheentriesinthedirectory？（）

填空题 Given the following code, write a line of code that, when inserted at the indicated location, will make the overriding method in Extension invoke the overridden method in class Base on the current object.   class Base {   public void print() {   System.out.println("base");   }   }   class Extention extends Base {   public void print() {   System.out.println("extension");   // insert line of implementation here   }   }   public class Q294d {   public static void main(String args[]) {   Extention ext = new Extention();   ext.print();   }   }   Fill in a single line of implementation.（）