Package org.silverpeas.core.util

Class Mutable<T>

  • public final class Mutable<T>
extends Object

    A mutable value wrapper which may or may not contain a non-null value. If a value is present, isPresent() will return true and get() will return the value.

    Additional methods that depend on the presence or absence of a contained value are provided, such as orElse() (return a default value if value not present) and ifPresent() (execute a block of code if the value is present).

    Author:
    Yohann Chastagnier

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static <T> Mutable<T> empty()
      Returns an empty Mutable.
      boolean equals​(Object obj)
      Indicates whether some other object is "equal to" this Mutable.
      Mutable<T> filter​(Predicate<? super T> predicate)
      If a value is present, and the value matches the given predicate, return an Mutable describing the value, otherwise return an empty Mutable.
      <U> Mutable<U> flatMap​(Function<? super T,​Mutable<U>> mapper)
      If a value is present, apply the provided Mutable-bearing mapping function to it, return that result, otherwise return an empty Mutable.
      T get()
      If a value is present in this Mutable, returns the value, otherwise throws NoSuchElementException.
      int hashCode()
      Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
      void ifPresent​(Consumer<? super T> consumer)
      If a value is present, invoke the specified consumer with the value, otherwise do nothing.
      boolean is​(T value)
      Indicates id the given value is equal to the one of the Mutable instance.
      boolean isEmpty()
      Return true if no value is present, otherwise false.
      boolean isPresent()
      Return true if there is a value present, otherwise false.
      <U> Mutable<U> map​(Function<? super T,​? extends U> mapper)
      If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Mutable describing the result.
      static <T> Mutable<T> of​(T value)
      Returns an Mutable with the specified value.
      static <T> Mutable<T> ofNullable​(T value)
      Returns an Mutable with the specified value which can be null.
      T orElse​(T other)
      Return the value if present, otherwise return other.
      T orElseGet​(Supplier<? extends T> other)
      Return the value if present, otherwise invoke other and return the result of that invocation.
      <X extends Throwable>
      T      		 orElseThrow​(Supplier<? extends X> exceptionSupplier)
      Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
      void set​(T value)
      Sets the value of the Mutable instance.
      String toString()
      Returns a non-empty string representation of this Mutable suitable for debugging.

    • Method Detail

      • of

        public static <T> Mutable<T> of​(T value)
        Returns an Mutable with the specified value.
        Type Parameters:
        T - the class of the value
        Parameters:
        value - the value to be present, which must be non-null
        Returns:
        an Mutable with the value present
        Throws:
        NullPointerException - if value is null

      • ofNullable

        public static <T> Mutable<T> ofNullable​(T value)
        Returns an Mutable with the specified value which can be null.
        Type Parameters:
        T - the class of the value
        Parameters:
        value - the value to be present, which must be null
        Returns:
        an Mutable with the value present

      • empty

        public static <T> Mutable<T> empty()
        Returns an empty Mutable. Its value is by default null.
        Type Parameters:
        T - class of the value.
        Returns:
        a Mutable with a null value.

      • get

        public T get()
        If a value is present in this Mutable, returns the value, otherwise throws NoSuchElementException.
        Returns:
        the non-null value held by this Mutable
        Throws:
        NoSuchElementException - if there is no value present
        See Also:
        isPresent()

      • set

        public void set​(T value)
        Sets the value of the Mutable instance.
        Parameters:
        value - the value to set.

      • is

        public boolean is​(T value)
        Indicates id the given value is equal to the one of the Mutable instance.
        Parameters:
        value - the value to verify.
        Returns:
        true if the value is equal to the wrapped one in this mutable. False otherwise.

      • isPresent

        public boolean isPresent()
        Return true if there is a value present, otherwise false.
        Returns:
        true if there is a value present, otherwise false

      • isEmpty

        public boolean isEmpty()
        Return true if no value is present, otherwise false.
        Returns:
        true if there is no value, otherwise false

      • ifPresent

        public void ifPresent​(Consumer<? super T> consumer)
        If a value is present, invoke the specified consumer with the value, otherwise do nothing.
        Parameters:
        consumer - block to be executed if a value is present
        Throws:
        NullPointerException - if value is present and consumer is null

      • filter

        public Mutable<T> filter​(Predicate<? super T> predicate)
        If a value is present, and the value matches the given predicate, return an Mutable describing the value, otherwise return an empty Mutable.
        Parameters:
        predicate - a predicate to apply to the value, if present
        Returns:
        an Mutable describing the value of this Mutable if a value is present and the value matches the given predicate, otherwise an empty Mutable
        Throws:
        NullPointerException - if the predicate is null

      • map

        public <U> Mutable<U> map​(Function<? super T,​? extends U> mapper)
        If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Mutable describing the result. Otherwise return an empty Mutable.
        Type Parameters:
        U - The type of the result of the mapping function
        Parameters:
        mapper - a mapping function to apply to the value, if present
        Returns:
        an Mutable describing the result of applying a mapping function to the value of this Mutable, if a value is present, otherwise an empty Mutable
        Throws:
        NullPointerException - if the mapping function is null
        API Note:
        This method supports post-processing on mutable values, without the need to explicitly check for a return status. For example, the following code traverses a stream of file names, selects one that has not yet been processed, and then opens that file, returning an Mutable<FileInputStream>: 
        
     Mutable<FileInputStream> fis =
         names.stream().filter(name -> !isProcessedYet(name))
                       .findFirst()
                       .map(name -> new FileInputStream(name));

        Here, findFirst returns an Mutable<String>, and then map returns an Mutable<FileInputStream> for the desired file if one exists.

      • flatMap

        public <U> Mutable<U> flatMap​(Function<? super T,​Mutable<U>> mapper)
        If a value is present, apply the provided Mutable-bearing mapping function to it, return that result, otherwise return an empty Mutable. This method is similar to map(Function), but the provided mapper is one whose result is already an Mutable, and if invoked, flatMap does not wrap it with an additional Mutable.
        Type Parameters:
        U - The type parameter to the Mutable returned by
        Parameters:
        mapper - a mapping function to apply to the value, if present the mapping function
        Returns:
        the result of applying an Mutable-bearing mapping function to the value of this Mutable, if a value is present, otherwise an empty Mutable
        Throws:
        NullPointerException - if the mapping function is null or returns a null result

      • orElse

        public T orElse​(T other)
        Return the value if present, otherwise return other.
        Parameters:
        other - the value to be returned if there is no value present, may be null
        Returns:
        the value, if present, otherwise other

      • orElseGet

        public T orElseGet​(Supplier<? extends T> other)
        Return the value if present, otherwise invoke other and return the result of that invocation.
        Parameters:
        other - a Supplier whose result is returned if no value is present
        Returns:
        the value if present otherwise the result of other.get()
        Throws:
        NullPointerException - if value is not present and other is null

      • orElseThrow

        public <X extends Throwable> T orElseThrow​(Supplier<? extends X> exceptionSupplier)
                                    throws X extends Throwable
        Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
        Type Parameters:
        X - Type of the exception to be thrown
        Parameters:
        exceptionSupplier - The supplier which will return the exception to be thrown
        Returns:
        the present value
        Throws:
        X - if there is no value present
        NullPointerException - if no value is present and exceptionSupplier is null
        X extends Throwable
        API Note:
        A method reference to the exception constructor with an empty argument list can be used as the supplier. For example, IllegalStateException::new

      • equals

        public boolean equals​(Object obj)
        Indicates whether some other object is "equal to" this Mutable. The other object is considered equal if:
        • it is also an Mutable and;
        • both instances have no value present or;
        • the present values are "equal to" each other via equals().
        Overrides:
        equals in class Object
        Parameters:
        obj - an object to be tested for equality
        Returns:
        {code true} if the other object is "equal to" this object otherwise false

      • hashCode

        public int hashCode()
        Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
        Overrides:
        hashCode in class Object
        Returns:
        hash code value of the present value or 0 if no value is present

      • toString

        public String toString()
        Returns a non-empty string representation of this Mutable suitable for debugging. The exact presentation format is unspecified and may vary between implementations and versions.
        Overrides:
        toString in class Object
        Returns:
        the string representation of this instance
        Implementation Requirements:
        If a value is present the result must include its string representation in the result. Empty and present Mutables must be unambiguously differentiable.