Can anyone knows?

Question

hi please answer this questions, if anyone knows
a) With C++, object reference counts are frequently used to keep track of
how many references to an object exist. Is there a need for such a reference
count for objects with Java? Please explain why or why not.
b) write a small pure Java program that computes the free disk space
of every disk drive available to the Java VM.
c) What is the difference between anonymous and abstract classes? Under what
circumstances would you be using anonymous classes?
Thanks

Answer 1

a) Garbage collector is responsible in java for counting references to objects and to free memory space when object is not referenced any more. Because Java manages memory transparently to programmer it is not neccessary to keep track of references.
b) to be done :)
c) abstarct classes are used to implement some common funcionality for descendand and left some details to be implemented in descendands eg. having class person:
public abstract class Person {
  String firstName;
  String lastName;
  public String getName() {
    return this.firstName + this.lastName
  abstract double calculateSalary();
then you can have two child classes eg. Worker and Manager implementing different logic in calculateSalary(). anonymous class is something like in-place implementation of class. It is used very often for implementing listeners interfaces in GUI application. eg:
  JButton button = new JButton("a button");
   button.addActionListener( new ActionListener() {
       public void actionPerformed(ActionEvent ev) {
          System.out.println("Anonymous class !!!!");
  });or to do something in new thread:
    (new Thread() {
        public void run() {
          //do something in new thread
    }).start();