Throwing multiple exceptions in a method of an interface in java

Question

I wanted to ask that how to mention this in my interface

public class find(int x) throws A_Exception, B_Exception{
----
----
---
}

i want to say that i can mention One exception in an interface but how to mention in my interface that my method will throw Two exceptions Namely A and B...

the code fragment mentioned above works only for A and not for B... Help

public interface dictionary{ 
   public void insert(int x) throws Dictionary_FullException, Duplicate_Element_FoundException; 
}
...
 public class SortedArray implements dictionary{ 
   public void insert(int x) throws Dictionary_FullException, Duplicate_Element_FoundException {
 ---------
}

but when i compile it ... it says..

SortedArray.java:66: insert(int) in assign.SortedArray cannot implement insert(int) in assign.dictionary; overridden method does not throw assign.SortedArray.Duplicate_Element_FoundException public void insert(int x) throws Dictionary_FullException

Answer 1

You can declare as many Exceptions as you want for your interface method. But the class you gave in your question is invalid. It should read

public class MyClass implements MyInterface {
  public void find(int x) throws A_Exception, B_Exception{
    ----
    ----
    ---
  }
}

Then an interface would look like this

public interface MyInterface {
  void find(int x) throws A_Exception, B_Exception;
}

Answer 2

I think you are asking for something like the code below:

public interface A
{
    void foo() 
        throws AException;
}

public class B
    implements A
{
    @Overrides 
    public void foo()
        throws AException,
               BException
    {
    }
}

This will not work unless BException is a subclass of AException. When you override a method you must conform to the signature that the parent provides, and exceptions are part of the signature.

The solution is to declare the the interface also throws a BException.

The reason for this is you do not want code like:

public class Main
{
    public static void main(final String[] argv)
    {
        A a;

        a = new B();

        try
        {
            a.foo();
        }
        catch(final AException ex)
        {
        }
        // compiler will not let you write a catch BException if the A interface
        // doesn't say that it is thrown.
    }
}

What would happen if B::foo threw a BException? The program would have to exit as there could be no catch for it. To avoid situations like this child classes cannot alter the types of exceptions thrown (except that they can remove exceptions from the list).

Answer 3

You need to specify it on the methods that can throw the exceptions. You just seperate them with a ',' if it can throw more than 1 type of exception. e.g.

public interface MyInterface {
  public MyObject find(int x) throws MyExceptionA,MyExceptionB;
}