Exception handling using Lambda in Java 8

Question

I'm doing some tests using lambda expressions but my code does not compile. My lambda implementation is wrong or the exception handling? What would be the correct implementation of the following code?

class MyObject { }

interface Creatable<T> {
    T create() throws IOException;
}

/* Using the code: */
Creatable<MyObject> creator = () ->  {
    try {
        return new MyObject();
    } catch (IOException e) {
        e.printStackTrace();
    }
};

MyObject obj1 = creator.create();

If i remove the try catch block and declare the exception to throw in the method, the code compiles and runs normally.

Creatable<MyObject> creator = () -> new MyObject();

The compilation error is:

incompatible types: bad return type in lambda expression

This actually doesn't have much to do with the lambda. The same method body won't compile if you declare it the normal way. The error message just isn't particularly informative. — Radiodef
– Radiodef, Commented Jun 3, 2014 at 0:50

assylias · Accepted Answer · 2014-06-03 00:42:14Z

6

Your lambda needs to return a MyObject. If the try block completes successfully that is the case, but if it doesn't the catch block is executed which does not return anything. So you could write:

Creatable<MyObject> creator = () ->  {
    try {
        return new MyObject();
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
};

But then you will get another compile error: "IOException is never thrown in try block". So you would also need to have a constructor in MyObject that throws an IOException:

class MyObject { MyObject() throws IOException {} }

In the end, unless MyObject actually throws an exception, you can simply use:

Creatable<MyObject> creator = () -> new MyObject();

which you can also write:

Creatable<MyObject> creator = MyObject::new;

edited Jun 3, 2014 at 0:42

answered Jun 3, 2014 at 0:36

assylias

330k84 gold badges680 silver badges806 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

glglgl Over a year ago

Even if new MyObject() theos an exception, you can write it like that. In any case, the user of this interface must be prepared to get an IOException out of it. That's the point of implementing the interface in exactly this way.

Malik Firose · Accepted Answer · 2018-12-24 05:09:14Z

1

Lambda needs all paths to return the value as mentioned in the previous answer the easy solution is to return at the end of the catch block

However there is a more elegant way to handle exception when using lambda

you can wrap a lambda with another Example wrap(((x,y)->x/y))

Biconsumer<Integer,Integer> consumer wrap(Biconsumer<Integer,Integer> consumer)    
{    
return (v,k)->{try

{consumer.apply()}

catch(){};

}

https://www.youtube.com/watch?v=YLKMCPMLv60&list=PLqq-6Pq4lTTa9YGfyhyW2CqdtW9RtY-I3&index=18

answered Dec 24, 2018 at 5:09

Malik Firose

4191 gold badge6 silver badges15 bronze badges

Comments

Sandeep Kumar · Accepted Answer · 2019-10-09 05:22:34Z

0

@FunctionalInterface
public interface CreateThrowable<T, R, E extends Throwable> {
   R create(T t) throws E;
static <T, R, E extends Throwable> Function<T, R> uncheckedException(ThrowingFunction<T, R, E> f) {
    return t -> {
        try {
            return f.create(t);
        } catch (Throwable e) {
            throw new RuntimeException(e);
        }
    };
}

}

answered Oct 9, 2019 at 5:22

Sandeep Kumar

705 bronze badges

Collectives™ on Stack Overflow

Exception handling using Lambda in Java 8

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related