Autocloseable in Java

Java7 is out since a few years & so try-with-resources in Java7.
​You might have already seen how this is working in new try-catch blocks.
​So below I am just giving one sample to create your autocloseable class to use & you can see the difference,
as you can return exceptions accordingly & which may be useful -

​Below is our custom Autocloseable class which we will use in our next class to check the difference & I have put the comments in the code itself which you can read for better understanding & have given the output also-

public class CustomAutoCloseable implements AutoCloseable {
 static private boolean isOpen = false;
 public CustomAutoCloseable() throws CustomException {
  if(isOpen) {
   throw new CustomException();
  }
  isOpen = true;  
 }
 public int add(int a, int b) throws Exception {
  if(a < 0 || b < 0)
   throw new Exception("Addition Exception......");
  return a+b;
 }
 @Override
 public void close() throws Exception {
  isOpen = false;
  /*if(isOpen)
   isOpen = false;
  else
   throw new Exception("Exception from close()......");*/
  throw new Exception("Exception from close()......");
 }
}
class CustomException extends Exception {
 private static final long serialVersionUID = 1L;
 public CustomException() {
  super("AutoCloseable Constructor Exception");
 }
}
--------------------------------------------------------------------------------------------------

public class Testing {
 public static void main(String[] args) throws Exception {
  try {
   check();
  } catch(Exception e) {
   System.out.println(e.getMessage());
  }
  System.out.println("--------------------------------");
  try {
   check1();
  } catch(Exception e) {
   System.out.println("Suppressed Exception - " + e.getSuppressed()[0].getMessage());
   System.out.println("Main exception - " + e.getMessage());
  }
  System.out.println("--------------------------------");
  try {
   check2();
  } catch(Exception e) {
   System.out.println("Suppressed Exception - " + e.getSuppressed()[0].getMessage());
   System.out.println("Main exception - " + e.getMessage());
  }
  System.out.println("--------------------------------");
  try {
   check3();
  } catch(Exception e) {
   //   Below API will get no information about the suppressed exception
   //   as there is no such exception as part of CustomAutoCloseable class
   //   So it will give RuntimeException if uncommented.
   //   System.out.println(e.getSuppressed()[0].getMessage());
   System.out.println(e.getMessage());
  }
  System.out.println("--------------------------------");
  try {
   check4();
  } catch(Exception e) {
   //   Though below API exists but it doesn't get the supressed exception's information
   //   as not using new try catch block. So it will through RuntimeException if uncommented.
   //   System.out.println(e.getSuppressed()[0].getMessage());
   System.out.println(e.getMessage());
  }
 }
 /**
  * Below method is having one exception condition which will arise
  * in close() of CustomAutoCloseable & will be returned back from
  * finally block below.
  * @throws Exception
  */
 public static void check() throws Exception {
  try(CustomAutoCloseable ca = new CustomAutoCloseable()) {
   System.out.println(ca.add(2, 3));
  } finally {
   System.out.println("In check finally...........");
  }
 }
 /**
  * Below method has 2 exception conditions - one from add() & second from close()
  * So here exception from add() is more useful but exception from close() will be
  * suppressed here and the calling method will get the exception from add() as
  * main exception.
  * @throws Exception
  */
 public static void check1() throws Exception {
  try(CustomAutoCloseable ca = new CustomAutoCloseable()) {
   System.out.println(ca.add(2, -3));
  } finally {
   System.out.println("In check1 finally...........");
  }
 }
 /**
  * Here we are not throwing any separate exception from finally block
  * so actual exception from constructor of CustomAutoCloseable will be
  * returned back along with the exception from close() as suppressed
  * exception.
  * @throws Exception
  */
 public static void check2() throws Exception {
  try(CustomAutoCloseable ca = new CustomAutoCloseable();
    CustomAutoCloseable ca1 = new CustomAutoCloseable()) {
   System.out.println(ca.add(2, 3));
  } finally {
   System.out.println("In check2 finally............");
  }
 }
 /**
  * Below finally block is throwing exception which is not generating
  * from try block, so it will replace the original exception which is
  * thrown from constructor of CustomAutoCloseable & we lose this info.
  * @throws Exception
  */
 public static void check3() throws Exception {
  try(CustomAutoCloseable ca = new CustomAutoCloseable();
    CustomAutoCloseable ca1 = new CustomAutoCloseable()) {
   System.out.println(ca.add(2, 3));
  } finally {
   throw new Exception("Thrown from check3 finally block.........");
  }
 }
 /**
  * Below method has 2 exception conditions - one from add() & second from close()
  * as closing twice here. So here exception from add() is more useful but it will
  * be replaced by exception close() while returning & we don't get the required
  * information while using old try-catch block
  * @throws Exception
  */
 public static void check4() throws Exception {
  CustomAutoCloseable ca = new CustomAutoCloseable();
  try {
   ca.close();
   System.out.println(ca.add(2, -3));
  } finally {
   System.out.println("In check4 finally............");
   ca.close();
  }
 }
}
---------------------------------------------------------------------------------
​Output :-

5
In check finally...........
Exception from close()......
--------------------------------
In check1 finally...........
Suppressed Exception - Exception from close()......
Main exception - Addition Exception......
--------------------------------
In check2 finally............
Suppressed Exception - Exception from close()......
Main exception - AutoCloseable Constructor Exception
--------------------------------
Thrown from check3 finally block.........
--------------------------------
In check4 finally............
Exception from close()......


Note :- If using Java8 or higher, then check this also - Autocleable in Java8