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FlexDoc/Javadoc 2.0 Demo Java Doc |
Class Optional<T>
java.util.Optional<T>
Type Parameters:
public final class Optional<T>
A container object which may or may not contain a non-
null value.
If a value is present,
isPresent() returns
true. If no
value is present, the object is considered
empty and
isPresent() returns
false.
Additional methods that depend on the presence or absence of a contained
value are provided, such as orElse()
(returns a default value if no value is present) and
ifPresent() (performs an
action if a value is present).
This is a value-based
class; programmers should treat instances that are
equal as interchangeable and should not
use instances for synchronization, or unpredictable behavior may
occur. For example, in a future release, synchronization may fail.
Since:
1.8
Method Summary |
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Returns an empty Optional instance.
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boolean |
Indicates whether some other object is "equal to" this Optional.
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If a value is present, and the value matches the given predicate,
returns an Optional describing the value, otherwise returns an
empty Optional.
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If a value is present, returns the result of applying the given
Optional-bearing mapping function to the value, otherwise returns
an empty Optional.
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If a value is present, returns the value, otherwise throws
NoSuchElementException.
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int |
Returns the hash code of the value, if present, otherwise 0
(zero) if no value is present.
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void |
If a value is present, performs the given action with the value,
otherwise does nothing.
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void |
If a value is present, performs the given action with the value,
otherwise performs the given empty-based action.
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boolean |
If a value is not present, returns true, otherwise
false.
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boolean |
If a value is present, returns true, otherwise false.
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If a value is present, returns an Optional describing (as if by
ofNullable(T)) the result of applying the given mapping function to
the value, otherwise returns an empty Optional.
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Returns an Optional describing the given non-null
value.
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Returns an Optional describing the given value, if
non-null, otherwise returns an empty Optional.
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If a value is present, returns an Optional describing the value,
otherwise returns an Optional produced by the supplying function.
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If a value is present, returns the value, otherwise returns
other.
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If a value is present, returns the value, otherwise returns the result
produced by the supplying function.
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If a value is present, returns the value, otherwise throws
NoSuchElementException.
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If a value is present, returns the value, otherwise throws an exception
produced by the exception supplying function.
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If a value is present, returns a sequential Stream containing
only that value, otherwise returns an empty Stream.
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Returns a non-empty string representation of this Optional
suitable for debugging.
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Methods inherited from class java.lang. Object |
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Returns an empty
Optional instance. No value is present for this
Optional.
Type Parameters:
T - The type of the non-existent value
Returns:
an empty Optional
Returns an
Optional describing the given non-
null
value.
Type Parameters:
T - the type of the value
Parameters:
value - the value to describe, which must be non-null
Returns:
an Optional with the value present
Throws:
Returns an
Optional describing the given value, if
non-
null, otherwise returns an empty
Optional.
Type Parameters:
T - the type of the value
Parameters:
value - the possibly-null value to describe
Returns:
an Optional with a present value if the specified value
is non-null, otherwise an empty Optional
If a value is present, returns the value, otherwise throws
NoSuchElementException.
Returns:
the non-null value described by this Optional
Throws:
public boolean isPresent |
() |
If a value is present, returns
true, otherwise
false.
Returns:
true if a value is present, otherwise false
public boolean isEmpty |
() |
If a value is not present, returns
true, otherwise
false.
Returns:
true if a value is not present, otherwise false
Since:
11
If a value is present, performs the given action with the value,
otherwise does nothing.
Parameters:
action - the action to be performed, if a value is present
Throws:
public void ifPresentOrElse |
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If a value is present, performs the given action with the value,
otherwise performs the given empty-based action.
Parameters:
action - the action to be performed, if a value is present
emptyAction - the empty-based action to be performed, if no value is
present
Throws:
NullPointerException - if a value is present and the given action
is
null, or no value is present and the given empty-based
action is
null.
Since:
9
If a value is present, and the value matches the given predicate,
returns an
Optional describing the value, otherwise returns an
empty
Optional.
Parameters:
predicate - the predicate to apply to a value, if present
Returns:
an Optional describing the value of this
Optional, if a value is present and the value matches the
given predicate, otherwise an empty Optional
Throws:
If a value is present, returns an
Optional describing (as if by
ofNullable(T)) the result of applying the given mapping function to
the value, otherwise returns an empty
Optional.
If the mapping function returns a null result then this method
returns an empty Optional.
Type Parameters:
U - The type of the value returned from the mapping function
Parameters:
mapper - the mapping function to apply to a value, if present
Returns:
an Optional describing the result of applying a mapping
function to the value of this Optional, if a value is
present, otherwise an empty Optional
Throws:
If a value is present, returns the result of applying the given
Optional-bearing mapping function to the value, otherwise returns
an empty
Optional.
This method is similar to map(Function), but the mapping
function is one whose result is already an Optional, and if
invoked, flatMap does not wrap it within an additional
Optional.
Type Parameters:
U - The type of value of the
Optional returned by the
mapping function
Parameters:
mapper - the mapping function to apply to a value, if present
Returns:
the result of applying an Optional-bearing mapping
function to the value of this Optional, if a value is
present, otherwise an empty Optional
Throws:
If a value is present, returns an
Optional describing the value,
otherwise returns an
Optional produced by the supplying function.
Parameters:
supplier - the supplying function that produces an Optional
to be returned
Returns:
returns an Optional describing the value of this
Optional, if a value is present, otherwise an
Optional produced by the supplying function.
Throws:
Since:
9
If a value is present, returns a sequential
Stream containing
only that value, otherwise returns an empty
Stream.
Returns:
the optional value as a Stream
Since:
9
If a value is present, returns the value, otherwise returns
other.
Parameters:
other - the value to be returned, if no value is present.
May be null.
Returns:
the value, if present, otherwise other
If a value is present, returns the value, otherwise returns the result
produced by the supplying function.
Parameters:
supplier - the supplying function that produces a value to be returned
Returns:
the value, if present, otherwise the result produced by the
supplying function
Throws:
If a value is present, returns the value, otherwise throws
NoSuchElementException.
Returns:
the non-null value described by this Optional
Throws:
Since:
10
If a value is present, returns the value, otherwise throws an exception
produced by the exception supplying function.
Type Parameters:
X - Type of the exception to be thrown
Parameters:
exceptionSupplier - the supplying function that produces an
exception to be thrown
Returns:
the value, if present
Throws:
X - if no value is present
Indicates whether some other object is "equal to" this
Optional.
The other object is considered equal if:
- it is also an Optional and;
- both instances have no value present or;
- the present values are "equal to" each other via equals().
Overrides:
Parameters:
obj - an object to be tested for equality
Returns:
true if the other object is "equal to" this object
otherwise false
See Also:
Returns the hash code of the value, if present, otherwise
0
(zero) if no value is present.
Overrides:
Returns:
hash code value of the present value or 0 if no value is
present
See Also:
Returns a non-empty string representation of this
Optional
suitable for debugging. The exact presentation format is unspecified and
may vary between implementations and versions.
Implementation Requirements:
If a value is present the result must include its string representation
in the result. Empty and present Optionals must be unambiguously
differentiable.
Overrides:
Returns:
the string representation of this instance
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