org.perro.functions.supplier

Class SupplierUtils

java.lang.Object

org.perro.functions.supplier.SupplierUtils

public final class SupplierUtils
extends java.lang.Object

Methods that build suppliers, specifically those involving arbitrary object types.

Method Summary

Modifier and Type	Method and Description
static <T,U> org.perro.functions.supplier.ConstantValues<T,U>	constantValues(T left, U right) Builds an object representing a pair of constant values of type <T> and <U> to be used as the second parameter to the above supplier(BiFunction, ConstantValues) method.
static <T,U,R> java.util.function.Supplier<R>	lazySupplier(java.util.function.BiFunction<T,U,R> function, org.perro.functions.supplier.ConstantValues<T,U> constants) First creates a supplier using the supplier(BiFunction, ConstantValues) method, and turns it into a lazy supplier.
static <T,R> java.util.function.Supplier<R>	lazySupplier(java.util.function.Function<T,R> function, T value) First creates a supplier using the supplier(Function, Object) method, and turns it into a lazy supplier.
static <T> java.util.function.Supplier<T>	lazySupplier(java.util.function.Supplier<T> supplier) Takes a Supplier and turns it into a lazy supplier.
static <T,U,R> java.util.function.Supplier<R>	supplier(java.util.function.BiFunction<T,U,R> function, org.perro.functions.supplier.ConstantValues<T,U> constants) Builds a Supplier of objects of type <R> from a passed BiFunction taking parameters of type <T> and <U>.
static <T,R> java.util.function.Supplier<R>	supplier(java.util.function.Function<T,R> function, T value) Builds a Supplier of objects of type <R> from a passed Function taking a parameter of type <T>.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

supplier

public static <T,R> java.util.function.Supplier<R> supplier(java.util.function.Function<T,R> function,
                                                            T value)

Builds a Supplier of objects of type <R> from a passed Function taking a parameter of type <T>. This can be very useful in the situation where you have a reference to a method that takes an object of type <T>, and an object to be passed to that method reference, which will be used for every invocation of it. In the following example we want to find the first order line item in an order, with a quantity greater than zero (assume there are static imports for the classes in this library):

     private OrderLineItem getFirstItemWithQuantity(Order order) {
         String errorMessage = "Order must contain a line item with non-zero quantity";
         return defaultStream(order.getLineItems())
             .filter(intGt(OrderLineItem::getQuantity))
             .findFirst()
             .orElseThrow(supplier(IllegalArgumentException::new, errorMessage));
     }
 

Type Parameters:

T - The type of the parameter to the passed Function. Also the type of the constant value passed to this method.

R - The return type of the passed Function, and the Supplier built by this method.

Parameters:

function - A Function to be used to build a supplier of values of type <R>.

value - A constant value of type <T> to be passed to every invocation of the above Function.

Returns:

A Supplier built from the passed Function and constant value of type <T>.

supplier

public static <T,U,R> java.util.function.Supplier<R> supplier(java.util.function.BiFunction<T,U,R> function,
                                                              org.perro.functions.supplier.ConstantValues<T,U> constants)

Builds a Supplier of objects of type <R> from a passed BiFunction taking parameters of type <T> and <U>. This can be very useful in the situation where you have a reference to a method that takes parameters of type <T> and <U>, and an object representing a pair of constant values to be passed to every invocation of that method reference. In the following example we want to find the first order line item in an order, with a quantity greater than zero (assume there are static imports for the classes in this library):

     private OrderLineItem getFirstItemWithQuantity(Order order, String customerId) {
         return defaultStream(order.getLineItems())
             .filter(intGt(OrderLineItem::getQuantity))
             .findFirst()
             .orElseThrow(supplier(this::buildNonZeroQuantityException, order.getId(), customerId));
     }

     private RuntimeException buildNonZeroQuantityException(String orderId, String customerId) {
         String errorMessage = "Order must contain a line item with non-zero quantity - orderId: %s, customerId: %s";
         return new IllegalArgumentException(String.format(errorMessage, orderId, customerId));
     }
 

Type Parameters:

T - The type of the first parameter to the passed BiFunction. Also the type of the first constant value in the constants pair passed to this method.

U - The type of the second parameter to the passed BiFunction. Also the type of the second constant value in the constants pair passed to this method.

R - The return type of the passed Function, and the Supplier built by this method.

Parameters:

function - A BiFunction taking arguments of type <T> and <U>, to be used to build a supplier of values of type <R>.

constants - An object representing a pair of constant values of type <T> and <U>, to be passed to every invocation of the above BiFunction. This value should be supplied via a call to the constantValues(Object, Object) method.

Returns:

A Supplier built from the passed BiFunction and object representing a pair of constant values of type <T> and <U>.

lazySupplier

public static <T> java.util.function.Supplier<T> lazySupplier(java.util.function.Supplier<T> supplier)

Takes a Supplier and turns it into a lazy supplier. The behavior is that the passed supplier is called only the first time a value is retrieved, and caches its result for subsequent invocations. Useful in many situations where retrieving a value is an expensive operation, such as retrieving an object from a database, or calling a micro-service.

Type Parameters:

T - The type of the object to be retrieved lazily.

Parameters:

supplier - A supplier to be called only once, and whose result will be cached.

Returns:

A lazy supplier of a value.

lazySupplier

public static <T,R> java.util.function.Supplier<R> lazySupplier(java.util.function.Function<T,R> function,
                                                                T value)

First creates a supplier using the supplier(Function, Object) method, and turns it into a lazy supplier. The behavior is that the passed supplier is called only the first time a value is retrieved, and caches its result for subsequent invocations. Useful in many situations where retrieving a value is an expensive operation, such as retrieving an object from a database, or calling a micro-service.

Type Parameters:

T - The type of the parameter to the passed Function. Also the type of the constant value passed to this method.

R - The return type of the passed Function, and the lazy Supplier built by this method.

Parameters:

function - A Function to be used to build a supplier of a value of type <R>.

value - A constant value of type <T> to be passed to the single invocation of the above Function.

Returns:

A lazy Supplier built from the passed Function and constant value of type <T>.

lazySupplier

public static <T,U,R> java.util.function.Supplier<R> lazySupplier(java.util.function.BiFunction<T,U,R> function,
                                                                  org.perro.functions.supplier.ConstantValues<T,U> constants)

First creates a supplier using the supplier(BiFunction, ConstantValues) method, and turns it into a lazy supplier.

Type Parameters:

T - The type of the first parameter to the passed BiFunction. Also the type of the first constant value in the constants pair passed to this method.

U - The type of the second parameter to the passed BiFunction. Also the type of the second constant value in the constants pair passed to this method.

R - The return type of the passed Function, and the lazy Supplier built by this method.

Parameters:

function - A BiFunction taking arguments of type <T> and <U>, to be used to build a lazy supplier of a value of type <R>.

constants - An object representing a pair of constant values of type <T> and <U>, to be passed to the single invocation of the above BiFunction. This value should be supplied via a call to the constantValues(Object, Object) method.

Returns:

A lazy Supplier built from the passed BiFunction and object representing a pair of constant values of type <T> and <U>.

constantValues

public static <T,U> org.perro.functions.supplier.ConstantValues<T,U> constantValues(T left,
                                                                                    U right)

Builds an object representing a pair of constant values of type <T> and <U> to be used as the second parameter to the above supplier(BiFunction, ConstantValues) method.

Type Parameters:

T - The type of the first constant in the pair built by this method.

U - The type of the second constant in the pair built by this method.

Parameters:

left - A value of type <T> representing the first constant in the pair built by this method.

right - A value of type <U> representing the second constant in the pair built by this method.

Returns:

An object representing a pair of constant values.