finalize question

[mohamed hamdy]

what will happen if a checked exception is thrown from the code of finalize() method when the object is to be garbage collected?

[Francis Siu]

hi mohamed

what will happen if a checked exception is thrown from the code of finalize() method ?when the object is to be garbage collected?

Let me use some coding to point out what happen if a checked exception is thrown from the code of finalize() method ?

public static void main(String[] argv)
{
try
{
finalize();//(c)
}
catch(IOException ioE)
{
System.out.println("file point to null");//(d)
}
finally
{
System.out.println("Finish");(e)
}
}
public static void finalize() throws IOException
{
File file=null;
FileWriter fw =new FileWriter(file); //(a)
System.out.prinln("Arrive forest"); //(b)
}

if a checked exception is thrown from the code of finalize() method,
firstly,(a) exception occur,it will jump out the method and create the IOException object,so (b) is not excecuted
then,the IOException object catch from the catch IOException handler,so print
file point to null (d)
And the IOException object will be collected after this catch handler,then print
Finish (e)
If it is not clear,please post again

[Francis Siu]

oo....
It may be easy to read

 
public static void main(String[] argv)
{
  try
  {
    finalize();//(c)
  }
  catch(IOException ioE)
  {
    System.out.println("file point to null");//(d)
  }
  finally
  {
    System.out.println("Finish");(e)
  }
}
public static void finalize() throws IOException
{
  File file=null;
  FileWriter fw =new FileWriter(file); //(a)
  System.out.prinln("Arrive forest"); //(b)
}
 

if a checked exception is thrown from the code of finalize() method,
firstly,(a) exception occur,create the IOException object and it will jump/throw out the method and terminate executing the remain part of programme
so (b) is not excecuted
then,the IOException object catch from the IOException handler,so print
file point to null (d)
And the IOException object will be collected after this catch handler,then print
Finish (e)
This time may be ok

[Marlene Miller]

If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates. Object API, finalize()

When I first read that sentence from the API, I thought it meant the finalize method ignored the exception. But the Java Programming Language says

This method is declared to throw any exception but if an exception occurs it is ignored *by the garbage collector*.

To find out what happens in the finalize() method I ran this test.

import java.util.Date;
class C {
   boolean throwIt;
   C(boolean b) { throwIt = b; }
//
   public void finalize() throws Throwable {
      try {
         System.out.println("finalize : try block");
         if (throwIt) throw new Throwable();
      } finally {
         System.out.println("finalize : finally block");
      }
      System.out.println("finalize : after try statement");
   }
}
//
class Test {
   boolean flag = true;
//
   void m(boolean b) {
      Runtime rt = Runtime.getRuntime();
//
      for (int i = 0; i < 10000; i++) {
         Date d = new Date();
         d = null;
      }
      C c = new C(b);
      c = null;
//
      System.out.println("before gc: " + rt.freeMemory());
      System.gc();
      System.out.println("after gc : " + rt.freeMemory());
   }
//
   public static void main(String[] args) {
      new Test().m(true);
      new Test().m(false);
   }
}