Package aQute.bnd.service.result

Interface Result<V,E>

Type Parameters:
V - The value type of the Result.
E - The error type of the Result.
All Known Implementing Classes:
Err, Ok
public interface Result<V,E>
The Result type is an alternative way of chaining together functions in a functional programming style while hiding away error handling structures such as try-catch-blocks and conditionals.
Instead of adding a throws declaration to a function, the return type of the function is instead set to Result<V, E> where V is the original return type, i.e. the "happy case" and E is the error type, usually the Exception type or a String if an error explanation is sufficient.

Example: 
 public Result<Float, String> divide(int a, int b) {
        if (b == 0) {
                return Result.err("Can't divide by zero!");
        } else {
                return Result.ok(a / b);
        }
 }

  • Method Details

    • of

      static <V, E> Result<V,E> of(V value, E error)
      Returns an Ok if the value parameter is non-null or an Err otherwise. Either one of value or error must not be null.
      Type Parameters:
      V - The value type of the Result.
      E - The error type of the Result.
      Parameters:
      value - If non-null, an Ok result is returned with the specified value.
      error - If value is null, an Err result is returned with the specified error.
      Returns:
      An Ok if the value parameter is non-null or an Err otherwise.

    • ok

      static <V, E> Result<V,E> ok(V value)
      Returns an Ok containing the specified value.
      Type Parameters:
      V - The value type of the Result.
      E - The error type of the Result.
      Parameters:
      value - The value to contain in the Ok result. Must not be null.
      Returns:
      An Ok result.

    • err

      static <V, E> Result<V,E> err(E error)
      Returns an Err containing the specified error.
      Type Parameters:
      V - The value type of the Result.
      E - The error type of the Result.
      Parameters:
      error - The error to contain in the Err result. Must not be null.
      Returns:
      An Err result.

    • err

      static <V> Result<V,String> err(String format, Object... args)

    • isOk

      boolean isOk()
      Returns true if this instance represents an Ok value, false otherwise.
      Returns:
      true if this instance represents an Ok value, false otherwise.

    • isErr

      boolean isErr()
      Returns true if this instance represents an Err value, false otherwise.
      Returns:
      true if this instance represents an Err value, false otherwise.

    • value

      Optional<V> value()
      Returns the value of this instance as an Optional. Returns Optional.empty() if this is an Err instance.
      Returns:
      The value of this instance as an Optional. Returns Optional.empty() if this is an Err instance.

    • error

      Optional<E> error()
      Returns the error of this instance as an Optional. Returns Optional.empty() if this is an Ok instance.
      Returns:
      The error of this instance as an Optional. Returns Optional.empty() if this is an Ok instance.

    • unwrap

      V unwrap()
      Returns the contained value if this is an Ok value. Otherwise throws a ResultException.
      Returns:
      The contained value
      Throws:
      ResultException - If this is an Err instance.

    • unwrap

      V unwrap(String message)
      Express the expectation that this object is an Ok value. Otherwise throws a ResultException with the specified message.
      Parameters:
      message - The message to pass to a potential ResultException.
      Throws:
      ResultException - If this is an Err instance.

    • orElse

      V orElse(V orElse)
      Returns the contained value if this is an Ok value. Otherwise returns the specified alternate value.
      Parameters:
      orElse - The value to return if this is an Err instance.
      Returns:
      The contained value or the alternate value

    • orElseGet

      V orElseGet(Supplier<? extends V> orElseSupplier)
      Returns the contained value if this is an Ok value. Otherwise returns the alternate value supplied by the specified supplier.
      Parameters:
      orElseSupplier - The supplier to supply an alternate value if this is an Err instance. Must not be null.
      Returns:
      The contained value or the alternate value

    • orElseThrow

      <R extends Throwable> V orElseThrow(FunctionWithException<? super E,? extends R> throwableSupplier) throws R
      Returns the contained value if this is an Ok value. Otherwise throws the exception supplied by the specified function.
      Type Parameters:
      R - The exception type.
      Parameters:
      throwableSupplier - The supplier to supply an exception if this is an Err instance. Must not be null. The supplier must return a non-null result.
      Returns:
      The contained value.
      Throws:
      R - If this is an Err instance.

    • map

      <U> Result<U,E> map(FunctionWithException<? super V,? extends U> mapper)
      Map the contained value if this is an Ok value. Otherwise return this.
      Type Parameters:
      U - The new value type.
      Parameters:
      mapper - The function to map the contained value into a new value. Must not be null. The function must return a non-null value.
      Returns:
      A result containing the mapped value if this is an Ok value. Otherwise this.

    • mapErr

      <F> Result<V,F> mapErr(FunctionWithException<? super E,? extends F> mapper)
      Map the contained error if this is an Err value. Otherwise return this.
      Type Parameters:
      F - The new error type.
      Parameters:
      mapper - The function to map the contained error into a new error. Must not be null. The function must return a non-null error.
      Returns:
      A result containing the mapped error if this is an Err value. Otherwise this.

    • flatMap

      <U> Result<U,E> flatMap(FunctionWithException<? super V,? extends Result<? extends U,? extends E>> mapper)
      FlatMap the contained value if this is an Ok value. Otherwise return this.
      Type Parameters:
      U - The new value type.
      Parameters:
      mapper - The function to flatmap the contained value into a new result. Must not be null. The function must return a non-null result.
      Returns:
      The flatmapped result if this is an Ok value. Otherwise this.

    • recover

      Result<V,E> recover(FunctionWithException<? super E,? extends V> recover)
      Recover the contained error if this is an Err value. Otherwise return this.
      Parameters:
      recover - The function to recover the contained error into a new value. Must not be null. The function must return a non-null value.
      Returns:
      A result containing the new value if this is an Err value. Otherwise this.

    • accept

      void accept(ConsumerWithException<? super V> ok, ConsumerWithException<? super E> err)
      Terminal function that processes the result or the error
      Parameters:
      ok - the consumer called when ok
      err - the consumer called when not ok

    • asError

      <X> Result<X,E> asError()

    • unwrap

      <X extends Throwable> V unwrap(Function<E,X> constructor) throws X
      Throws:
      X extends Throwable