ExceptionalExceptionHandling.java

import java.io.IOException;

public class ExceptionalExceptionHandling {

    public static void main(String[] args) {
        ThrowingSupplier<IllegalStateException, String> wellTyped = () -> {
            throw new IllegalStateException();
        };

        ThrowingSupplier<RuntimeException, String> wellTypedButUnnecessary = () -> {
            throw new IllegalStateException();
        };

        ThrowingSupplier<RuntimeException, String> wellTypedButNotEnforcedBecauseUnchecked = () -> {
            if (false) {
                throw new IllegalStateException();
            } else {
                throw new IllegalArgumentException();
            }
        };

        ThrowingSupplier<Exception, String> wellTypedAndEnforcedBecauseChecked = () -> {
            if (false) {
                throw new IOException();
            } else {
                throw new NoSuchMethodException();
            }
        };

        ThrowingSupplier<IllegalStateException, String> illTypedAndUncaughtBecauseUnchecked = () -> {
            if (false) {
                throw new IllegalStateException();
            } else {
                throw new IllegalArgumentException();
            }
        };

        ThrowingSupplier<IOException, String> illTypedAndUncaughtBecauseMixedCheckedAndUnchecked = () -> {
            if (false) {
                throw new IOException();
            } else {
                throw new IllegalArgumentException();
            }
        };

        ThrowingSupplier<RuntimeException, String> illTypedAndCaughtBecauseChecked = () -> {
            if (false) {
                throw new IOException();
            } else {
                throw new IllegalArgumentException();
            }
        };

        ThrowingSupplier<IOException, String> illTypedAndCaughtBecauseBothChecked = () -> {
            if (false) {
                throw new IOException();
            } else {
                throw new NoSuchMethodException();
            }
        };
    }

    @FunctionalInterface
    public interface ThrowingSupplier<E extends Exception, T> {
        T apply() throws E;
    }
}