Throw an exception from within a lambda expression

Throwing Exceptions in Lambdas

• A lambda expression can throw exceptions.
• For checked exceptions:
• The exception thrown must be compatible with those listed in the throws clause of the abstract method of the functional interface.

Requirements for Checked Exceptions

• If lambda throws a checked exception (e.g. IOException):
• The abstract method of the functional interface must include the same exception in the throws clause.
• Without this clause, the lambda expression will be incompatible with the method and will cause a compilation error.

Example: Exception Throwing in Lambda
Code:

import java.io.*;

interface MyIOAction {
    boolean ioAction(Reader rdr) throws IOException;
}

class LambdaExceptionDemo {
    public static void main(String args[]) {
        // Esta lambda de bloco pode lançar uma IOException.
        // A cláusula throws deve estar presente em ioAction().
        MyIOAction myIO = (rdr) -> {
            int ch = rdr.read(); // Pode lançar IOException
            // Lógica adicional pode ser inserida aqui
            return true;
        };
    }
}

Explanation:
throws clause:

• The ioAction(Reader rdr) method in the MyIOAction functional interface includes throws IOException.
• This allows the lambda associated with the method to use operations that can throw IOException, such as rdr.read().

Error without throws Clause:

• If the throws IOException clause is removed from ioAction, the program does not compile.
• This occurs because the exception thrown by the lambda (IOException) is not handled or declared in the method.

Important Note:

• Compatibility between Lambdas and Functional Interfaces:
• A lambda expression must be compatible with the abstract method of the functional interface.
• For checked exceptions, this compatibility requires that exceptions thrown by the lambda are listed in the method's throws clause.

Practical Test:
Try removing the throws clause from ioAction in the code above. This will result in compilation error due to incompatibility between lambda and functional interface method.

The above is the detailed content of Throw an exception from within a lambda expression. For more information, please follow other related articles on the PHP Chinese website!