pack-priv final Class Absent<T>

Implements abstract com.google.common.base.Optional.asSet.

Doc from com.google.common.base.Optional.asSet.

Returns an immutable singleton Set whose only element is the contained instance if it is present; an empty immutable Set otherwise.

Comparison to java.util.Optional: this method has no equivalent in Java 8's Optional class. However, this common usage:

for (Foo foo : possibleFoo.asSet()) {
  doSomethingWith(foo);
}

possibleFoo.ifPresent(foo -> doSomethingWith(foo));

Java 9 users: some use cases can be written with calls to optional.stream().

Annotations

@Override

Implements abstract com.google.common.base.Optional.equals.

Doc from com.google.common.base.Optional.equals.

Returns true if object is an Optional instance, and either the contained references are equal to each other or both are absent. Note that Optional instances of differing parameterized types can be equal.

Comparison to java.util.Optional: no differences.

Parameters

object:Object

Doc from java.lang.Object.equals.

the reference object with which to compare.

Returns:boolean

Doc from java.lang.Object.equals.

true if this object is the same as the obj argument; false otherwise.

Annotations

@Override

Implements abstract com.google.common.base.Optional.get.

Doc from com.google.common.base.Optional.get.

Returns the contained instance, which must be present. If the instance might be absent, use or(Object) or orNull instead.

Comparison to java.util.Optional: when the value is absent, this method throws IllegalStateException, whereas the java.util counterpart throws NoSuchElementException.

Annotations

@Override

Implements abstract com.google.common.base.Optional.hashCode.

Doc from com.google.common.base.Optional.hashCode.

Returns a hash code for this instance.

Comparison to java.util.Optional: this class leaves the specific choice of hash code unspecified, unlike the Java 8+ equivalent.

Returns:int

Doc from java.lang.Object.hashCode.

a hash code value for this object

Annotations

@Override

Implements abstract com.google.common.base.Optional.isPresent.

Doc from com.google.common.base.Optional.isPresent.

Returns true if this holder contains a (non-null) instance.

Comparison to java.util.Optional: no differences.

Annotations

@Override

Implements abstract com.google.common.base.Optional.or.

Doc from com.google.common.base.Optional.or.

Returns the contained instance if it is present; defaultValue otherwise. If no default value should be required because the instance is known to be present, use get() instead. For a default value of null, use orNull.

Note about generics: The signature public T or(T defaultValue) is overly restrictive. However, the ideal signature, public <S super T> S or(S), is not legal Java. As a result, some sensible operations involving subtypes are compile errors:

Optional<Integer> optionalInt = getSomeOptionalInt();
Number value = optionalInt.or(0.5); // error

FluentIterable<? extends Number> numbers = getSomeNumbers();
Optional<? extends Number> first = numbers.first();
Number value = first.or(0.5); // error

As a workaround, it is always safe to cast an Optional<? extends T> to Optional<T>. Casting either of the above example Optional instances to Optional<Number> (where Number is the desired output type) solves the problem:

Optional<Number> optionalInt = (Optional) getSomeOptionalInt();
Number value = optionalInt.or(0.5); // fine

FluentIterable<? extends Number> numbers = getSomeNumbers();
Optional<Number> first = (Optional) numbers.first();
Number value = first.or(0.5); // fine

Comparison to java.util.Optional: this method is similar to Java 8's Optional.orElse, but will not accept null as a defaultValue (orNull must be used instead). As a result, the value returned by this method is guaranteed non-null, which is not the case for the java.util equivalent.

Annotations

@Override

Implements abstract com.google.common.base.Optional.or.

Doc from com.google.common.base.Optional.or.

Returns this Optional if it has a value present; secondChoice otherwise.

Comparison to java.util.Optional: this method has no equivalent in Java 8's Optional class; write thisOptional.isPresent() ? thisOptional : secondChoice instead.

Annotations

@SuppressWarnings:unchecked

@Override

Implements abstract com.google.common.base.Optional.or.

Doc from com.google.common.base.Optional.or.

Returns the contained instance if it is present; supplier.get() otherwise.

Comparison to java.util.Optional: this method is similar to Java 8's Optional.orElseGet, except when supplier returns null. In this case this method throws an exception, whereas the Java 8+ method returns the null to the caller.

Annotations

@Override

Implements abstract com.google.common.base.Optional.orNull.

Doc from com.google.common.base.Optional.orNull.

Returns the contained instance if it is present; null otherwise. If the instance is known to be present, use get() instead.

Comparison to java.util.Optional: this method is equivalent to Java 8's Optional.orElse(null).

Annotations

@Override

@CheckForNull

Implements abstract com.google.common.base.Optional.toString.

Doc from com.google.common.base.Optional.toString.

Returns a string representation for this instance.

Comparison to java.util.Optional: this class leaves the specific string representation unspecified, unlike the Java 8+ equivalent.

Returns:String

Doc from java.lang.Object.toString.

a string representation of the object

Annotations

@Override

Implements abstract com.google.common.base.Optional.transform.

Doc from com.google.common.base.Optional.transform.

If the instance is present, it is transformed with the given Function; otherwise, Optional#absent is returned.

Comparison to java.util.Optional: this method is similar to Java 8's Optional.map, except when function returns null. In this case this method throws an exception, whereas the Java 8+ method returns Optional.absent().

Annotations

@Override