What are the rules to follow while using exceptions in java lambda expressions?

Java 8 Object Oriented Programming Programming

The lambda expressions can't be executed on their own. It is used to implement methods that have declared in a functional interface. We need to follow a few rules in order to use the exception handling mechanism in a lambda expression.

Rules for Lambda Expression

A lambda expression cannot throw any checked exception until its corresponding functional interface declares a throws clause.
An exception thrown by any lambda expression can be of the same type or sub-type of the exception declared in the throws clause of its functional interface.

Example-1

interface ThrowException {
   void throwing(String message);
}
public class LambdaExceptionTest1 {
   public static void main(String[] args) {
      ThrowException te = msg -> {     // lambda expression
         throw new RuntimeException(msg); // RuntimeException is not a checked exception
      };
      te.throwing("Lambda Expression");
   }
}

Output

Exception in thread "main" java.lang.RuntimeException: Lambda Expression
   at LambdaExceptionTest1.lambda$main$0(LambdaExceptionTest1.java:8)
   at LambdaExceptionTest1.main(LambdaExceptionTest1.java:10)

Example-2

import java.io.*;

interface ThrowException {
   void throwing(String message) throws IOException;
}
public class LambdaExceptionTest2 {
   public static void main(String[] args) throws Exception {
      ThrowException te = msg -> {    // lambda expression
         throw new FileNotFoundException(msg); // FileNotFoundException is a sub-type of IOException
      };
      te.throwing("Lambda Expression");
   }
}

Output

Exception in thread "main" java.io.FileNotFoundException: Lambda Expression
   at LambdaExceptionTest2.lambda$main$0(LambdaExceptionTest2.java:9)
   at LambdaExceptionTest2.main(LambdaExceptionTest2.java:11)

Raja

Published on 20-Dec-2019 08:36:16

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