uk.kludje

Interface Nullifier<T,R>

Type Parameters:

T - the input

R - the result

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface Nullifier<T,R>

A functional interface with null-safe checks.

For use with getter chains where one or more elements in the chain can be null.

Example usage:

D d = Nullifier.eval(a, A::getB, B::getC, C::getD);

The above code is equivalent to:

   D d = null;
   if (a != null) {
     B b = a.getB();
     if (b != null) {
       C c  = b.getC();
       if (c != null) {
         d = c.getD();
       }
     }
   }
 

To test if d is null, use:

boolean dIsNull = Nullifier.isNull(a, A::getB, B::getC, C::getD);

Implement $apply(Object); invoke apply(Object).

Method Summary

Modifier and Type	Method and Description
R	$apply(T t) Implement this method with a lambda expression/method reference.
default <V> Nullifier<T,V>	andThenSpan(Nullifier<? super R,? extends V> after) Chains two instances together.
default R	apply(T t) If the argument is null, returns null; else invokes $apply(Object).
default R	applyOr(T t, R defaultValue) As apply(Object) except checked another value can be returned if the result would otherwise be null.
default R	applyOrGet(T t, java.util.function.Supplier<R> factory) As apply(Object) except checked another value can be returned if the result would otherwise be null.
static <A,B,C,D,E,Z> Z	eval(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends D> f2, Nullifier<? super D,? extends E> f3, Nullifier<? super E,? extends Z> f4)
static <A,B,C,D,Z> Z	eval(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends D> f2, Nullifier<? super D,? extends Z> f3)
static <A,B,C,Z> Z	eval(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends Z> f2)
static <A,B,Z> Z	eval(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends Z> f1) Convenience method for evaluating a chain of Nullifier calls.
static <A,Z> Z	eval(A a, Nullifier<? super A,? extends Z> f0)
static <A,B,C,D,E,Z> boolean	isNull(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends D> f2, Nullifier<? super D,? extends E> f3, Nullifier<? super E,? extends Z> f4)
static <A,B,C,D,Z> boolean	isNull(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends D> f2, Nullifier<? super D,? extends Z> f3)
static <A,B,C,Z> boolean	isNull(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends Z> f2)
static <A,B,Z> boolean	isNull(A a, Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends Z> f1) Convenience method for evaluating a chain of Nullifier calls to see if any link is null.
static <A,Z> boolean	isNull(A a, Nullifier<? super A,? extends Z> f0)
static <A,B,C,D,E,Z> Nullifier<A,Z>	span(Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends D> f2, Nullifier<? super D,? extends E> f3, Nullifier<? super E,? extends Z> f4)
static <A,B,C,D,Z> Nullifier<A,Z>	span(Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends D> f2, Nullifier<? super D,? extends Z> f3)
static <A,B,C,Z> Nullifier<A,Z>	span(Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends C> f1, Nullifier<? super C,? extends Z> f2)
static <A,B,Z> Nullifier<A,Z>	span(Nullifier<? super A,? extends B> f0, Nullifier<? super B,? extends Z> f1) Creates a null-safe chain of calls spanning possibly null call sites.

Method Detail

$apply

R $apply(T t)
  throws java.lang.Exception

Implement this method with a lambda expression/method reference.

Consumers should invoke apply(Object) and NOT call this method directly.

Parameters:

t - the argument; not null if invoked by default apply(Object)

Returns:

the result

Throws:

java.lang.Exception - on error

span

static <A,B,Z> Nullifier<A,Z> span(Nullifier<? super A,? extends B> f0,
                                   Nullifier<? super B,? extends Z> f1)

Creates a null-safe chain of calls spanning possibly null call sites.

The functions may not be null, but the inputs and outputs may be.

A number of overloaded methods are provided with varying argument counts.

Type Parameters:

A - the initial type

B - an intermediary type

Z - the resultant type

Parameters:

f0 - the initial function; MUST NOT be null

f1 - a subsequent function; MUST NOT be null

Returns:

a function checked, given A, returns Z, or null if any element in the chain is null

span

static <A,B,C,Z> Nullifier<A,Z> span(Nullifier<? super A,? extends B> f0,
                                     Nullifier<? super B,? extends C> f1,
                                     Nullifier<? super C,? extends Z> f2)

span

static <A,B,C,D,Z> Nullifier<A,Z> span(Nullifier<? super A,? extends B> f0,
                                       Nullifier<? super B,? extends C> f1,
                                       Nullifier<? super C,? extends D> f2,
                                       Nullifier<? super D,? extends Z> f3)

span

static <A,B,C,D,E,Z> Nullifier<A,Z> span(Nullifier<? super A,? extends B> f0,
                                         Nullifier<? super B,? extends C> f1,
                                         Nullifier<? super C,? extends D> f2,
                                         Nullifier<? super D,? extends E> f3,
                                         Nullifier<? super E,? extends Z> f4)

eval

static <A,Z> Z eval(A a,
                    Nullifier<? super A,? extends Z> f0)

eval

static <A,B,Z> Z eval(A a,
                      Nullifier<? super A,? extends B> f0,
                      Nullifier<? super B,? extends Z> f1)

Convenience method for evaluating a chain of Nullifier calls.

A number of overloaded methods are provided with varying argument counts.

Type Parameters:

A - the root type

B - an intermediary type

Z - the result type

Parameters:

a - the root object in the object graph (may be null)

f0 - is passed "a"; MUST NOT be null

f1 - is passed the result of "f0"; MUST NOT be null

Returns:

the result of the function chain or null

See Also:

eval(Object, Nullifier), eval(Object, Nullifier, Nullifier), eval(Object, Nullifier, Nullifier, Nullifier), eval(Object, Nullifier, Nullifier, Nullifier, Nullifier, Nullifier)

eval

static <A,B,C,Z> Z eval(A a,
                        Nullifier<? super A,? extends B> f0,
                        Nullifier<? super B,? extends C> f1,
                        Nullifier<? super C,? extends Z> f2)

eval

static <A,B,C,D,Z> Z eval(A a,
                          Nullifier<? super A,? extends B> f0,
                          Nullifier<? super B,? extends C> f1,
                          Nullifier<? super C,? extends D> f2,
                          Nullifier<? super D,? extends Z> f3)

eval

static <A,B,C,D,E,Z> Z eval(A a,
                            Nullifier<? super A,? extends B> f0,
                            Nullifier<? super B,? extends C> f1,
                            Nullifier<? super C,? extends D> f2,
                            Nullifier<? super D,? extends E> f3,
                            Nullifier<? super E,? extends Z> f4)

isNull

static <A,Z> boolean isNull(A a,
                            Nullifier<? super A,? extends Z> f0)

isNull

static <A,B,Z> boolean isNull(A a,
                              Nullifier<? super A,? extends B> f0,
                              Nullifier<? super B,? extends Z> f1)

Convenience method for evaluating a chain of Nullifier calls to see if any link is null.

A number of overloaded methods are provided with varying argument counts.

Equivalent to:

boolean isNull = (Nullifier.eval(a, f0, f1) == null);

Type Parameters:

A - the root type

B - an intermediary type

Z - the result type

Parameters:

a - the root object in the object graph (may be null)

f0 - is passed "a"; MUST NOT be null

f1 - is passed the result of "f0"; MUST NOT be null

Returns:

true if the result is null; false otherwise

See Also:

isNull(Object, Nullifier), isNull(Object, Nullifier, Nullifier), isNull(Object, Nullifier, Nullifier, Nullifier), isNull(Object, Nullifier, Nullifier, Nullifier, Nullifier, Nullifier)

isNull

static <A,B,C,Z> boolean isNull(A a,
                                Nullifier<? super A,? extends B> f0,
                                Nullifier<? super B,? extends C> f1,
                                Nullifier<? super C,? extends Z> f2)

isNull

static <A,B,C,D,Z> boolean isNull(A a,
                                  Nullifier<? super A,? extends B> f0,
                                  Nullifier<? super B,? extends C> f1,
                                  Nullifier<? super C,? extends D> f2,
                                  Nullifier<? super D,? extends Z> f3)

isNull

static <A,B,C,D,E,Z> boolean isNull(A a,
                                    Nullifier<? super A,? extends B> f0,
                                    Nullifier<? super B,? extends C> f1,
                                    Nullifier<? super C,? extends D> f2,
                                    Nullifier<? super D,? extends E> f3,
                                    Nullifier<? super E,? extends Z> f4)

apply

default R apply(T t)

If the argument is null, returns null; else invokes $apply(Object).

This method rethrows any exception thrown by $apply(Object) as an unchecked exception.

Parameters:

t - the input which may be null

Returns:

the result which may be null

See Also:

Exceptions.throwChecked(Throwable)

andThenSpan

default <V> Nullifier<T,V> andThenSpan(Nullifier<? super R,? extends V> after)

Chains two instances together.

Type Parameters:

V - the new result type

Parameters:

after - the nullifier to invoke after this; MUST NOT be null

Returns:

a new nullifier

applyOr

default R applyOr(T t,
                  R defaultValue)

As apply(Object) except checked another value can be returned if the result would otherwise be null.

Parameters:

t - the input which may be null

defaultValue - a default value

Returns:

the result which will not be null unless defaultValue is null

applyOrGet

default R applyOrGet(T t,
                     java.util.function.Supplier<R> factory)

As apply(Object) except checked another value can be returned if the result would otherwise be null.

Parameters:

t - the input which may be null

factory - result producer called for null cases

Returns:

the result which will not be null unless the factory also return null