Optional consistency

1. java.util.Optional

Optional An object is a wrapper object , As a safer way , Used instead of type T References to , It is used to solve the problems caused by the abnormal null index .

1.1 public static Optional empty()

Generate an empty Optional.

1.2 public static Optional of(T value)

Generate a with a given value Optional, If value by null, It will be thrown out. NullPointerException.

1.3 public static Optional ofNullable(T value)

Generate a with a given value Optional, If value by null, Will produce an empty Optional.

1.4 public T get()

Get current Optional Value , If at present Optional It's empty , Throw out NoSuchElementException.

1.5 public boolean isPresent()

If at present Optional Not empty , Then return to false.

1.6 public boolean isEmpty()

If at present Optional It's empty , Then return to true.

1.7 public void ifPresent(Consumer<? super T> action)

If at present Optional Not empty , Then execute the specified Consumer.

1.8 public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)

If at present Optional Not empty , Then execute the specified Consumer, Otherwise, execute the specified Runable.

1.9 public Optional filter(Predicate<? super T> predicate)

If at present Optional It's empty , Returns an empty Optional, Otherwise, execute the specified Predicate, If the execution result is true, Then return to the current Optional, Otherwise, it returns empty Optional.

1.10 public Optional map(Function<? super T, ? extends U> mapper)

Return to the current Optional The value of is passed to the specified Function And package the results into Optional, If at present Optional Is empty or Function Execution result is empty , It returns null Optional.

1.11 public Optional flatMap(Function<? super T, ? extends Optional<? extends U>> mapper)

Return to the current Optional The value of is passed to the specified Function After the results of the , If at present Optional Is empty or Function Execution result is empty , It returns null Optional, This method is similar to the above map The difference between the method and map Methods will Function The returned results are automatically wrapped into Optional type , and flatMap Methodical Function The returned result must be Optional type ,flatMap The return result of and Function The result remains the same .

1.12 public Optional or(Supplier<? extends Optional<? extends T>> supplier)

If at present Optional Not empty , Then return to the current Optional, Otherwise return to Supplier The result of execution , The result must be Optional type , if Supplier The result after execution is empty , Throw out NullPointerException.

1.13 public Stream stream()

If at present Optional It's empty , It returns null Stream, Otherwise, the return contains the current Optional The value of the Stream.

1.14 public T orElse(T other)

If at present Optional Not empty , Returns the current Optional Value , Otherwise, the specified object is returned other.

1.15 public T orElseGet(Supplier<? extends T> supplier)

If at present Optional Not empty , Returns the current Optional Value , Otherwise, return the specified Supplier Generated objects .

1.16 public T orElseThrow()

If at present Optional Not empty , Returns the current Optional Value , Otherwise throw NoSuchElementException.

1.17 public T orElseThrow(Supplier<? extends X> exceptionSupplier) throws

If at present Optional Not empty , Returns the current Optional Value , Otherwise, the specified Supplier Generated exception .

1.18 public boolean equals(Object obj)

A little .

1.19 public int hashCode()

A little .

1.20 public String toString()

A little .