com.github.houbb.heaven.util.util

类 Optional<T>

java.lang.Object

com.github.houbb.heaven.util.util.Optional<T>

public final class Optional<T>
extends Object

Optional 工具类 A container object 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. 此处简化 jdk8 Optional，提供一个简化版的 Optional提供给 jdk7 使用。便于过渡使用。

从以下版本开始:

0.0.9

方法概要

限定符和类型	方法和说明
static <T> Optional<T>	empty() Returns an empty Optional instance.
boolean	equals(Object obj) Indicates whether some other object is "equal to" this Optional.
T	get() If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.
<R> R	getCastOrNull(Class<R> rClass) 获取转换后的类型。
int	hashCode() Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
boolean	isNotPresent() Return true if there is a value not present, otherwise false.
boolean	isPresent() Return true if there is a value present, otherwise false.
static <T> Optional<T>	of(T value) Returns an Optional with the specified present non-null value.
static <T> Optional<T>	ofNullable(T value) Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
T	orDefault(T defaultVal) Return the contained value, if present, otherwise return default value.
T	orElseNull() Return the contained value, if present, otherwise return null.
<X extends Throwable> T	orElseThrow(X throwable) Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.
String	toString() Returns a non-empty string representation of this Optional suitable for debugging.

从类继承的方法 java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

方法详细资料

empty

public static <T> Optional<T> empty()

Returns an empty Optional instance. No value is present for this Optional. Though it may be tempting to do so, avoid testing if an object is empty by comparing with == against instances returned by Option.empty(). There is no guarantee that it is a singleton. Instead, use isPresent().

类型参数:

T - Type of the non-existent value

返回:

an empty Optional

of

public static <T> Optional<T> of(T value)

Returns an Optional with the specified present non-null value.

类型参数:

T - the class of the value

参数:

value - the value to be present, which must be non-null

返回:

an Optional with the value present

抛出:

NullPointerException - if value is null

ofNullable

public static <T> Optional<T> ofNullable(T value)

Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.

类型参数:

T - the class of the value

参数:

value - the possibly-null value to describe

返回:

an Optional with a present value if the specified value is non-null, otherwise an empty Optional

get

public T get()

If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.

返回:

the non-null value held by this Optional

抛出:

NoSuchElementException - if there is no value present

另请参阅:

isPresent()

getCastOrNull

public <R> R getCastOrNull(Class<R> rClass)

获取转换后的类型。 如果为空，则直接返回 null

类型参数:

R - 泛型

参数:

rClass - 类型

返回:

结果

从以下版本开始:

0.1.41

isPresent

public boolean isPresent()

Return true if there is a value present, otherwise false.

返回:

true if there is a value present, otherwise false

isNotPresent

public boolean isNotPresent()

Return true if there is a value not present, otherwise false.

返回:

true if there is a value not present, otherwise false

从以下版本开始:

0.1.6

orElseThrow

public <X extends Throwable> T orElseThrow(X throwable)
                                    throws X extends Throwable

Return the contained value, if present, otherwise throw an exception to be created by the provided supplier. A method reference to the exception constructor with an empty argument list can be used as the supplier. For example, IllegalStateException::new

类型参数:

X - 泛型

参数:

throwable - Type of the exception to be thrown be thrown

返回:

the present value

抛出:

X - if there is no value present

NullPointerException - if no value is present and exceptionSupplier is null

X extends Throwable

orElseNull

public T orElseNull()

Return the contained value, if present, otherwise return null.

返回:

the present value or null

从以下版本开始:

0.1.5

orDefault

public T orDefault(T defaultVal)

Return the contained value, if present, otherwise return default value.

参数:

defaultVal - default value

返回:

the present value or default value

从以下版本开始:

0.1.15

equals

public boolean equals(Object obj)

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().

覆盖:

equals 在类中 Object

参数:

obj - an object to be tested for equality

返回:

{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.

覆盖:

hashCode 在类中 Object

返回:

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 Optional suitable for debugging. The exact presentation format is unspecified and may vary between implementations and versions. If a value is present the result must include its string representation in the result. Empty and present Optionals must be unambiguously differentiable.

覆盖:

toString 在类中 Object

返回:

the string representation of this instance