Coalesce.java

    public interface CoalescingCallback<U> {
        U call();
    }



    /***
     * See documentation for coalesce(CoalescingCallback<T>, T)
     */
    public static <T> T coalesce(CoalescingCallback<T> expression) {
        return coalesce(expression, null);
    }

    /***
     * Null coalescing operator for Java. Not a real operator because custom operators are not allowed.
     * Together with lambda expressions, this allows compact null coalescing in java, meaning
     * coalesce(() -> foo.bar().toString()) would return null if any part of it is null. This avoids
     * a) cumbersome try-catch blocks or b) equally cumbersome if-else statements
     *
     * @param expression   The expression to be evaluated.
     * @param defaultValue Default value
     * @param <T>          Return type
     * @return The expected value of the expression, or null
     */
    public static <T> T coalesce(CoalescingCallback<T> expression, T defaultValue) {
        try {
            T result = expression.call();
            return result;
        } catch (NullPointerException e) {
            return defaultValue;
        }
    }