DoubleConsumer Interface in Java with Examples - GeeksforGeeks

09 Oct, 2018
The DoubleConsumer Interface is a part of the java.util.function package which has been introduced since Java 8, to implement functional programming in Java. It represents a function which takes in one double-valued argument but does not return any value.
The lambda expression assigned to an object of DoubleConsumer type is used to define its accept() which eventually applies the given operation on its only argument. It is similar to using an object of type Consumer<Double>
The DoubleConsumer interface consists of the following two functions:
This method accepts one value and performs the operation on its only argument.
Syntax:
void accept(double value)
Parameters: This method takes in only one parameter:
value– the input argument
Returns: This method does not return any value.
Below is the code to illustrate accept() method:
import java.util.function.DoubleConsumer;  public class GFG {    public static void main(String args[])    {          // Create a DoubleConsimer Instance        DoubleConsumer            display            = a -> System.out.println(a * 10);          // using accept() method        display.accept(3);    }}
30.0

It returns a composed DoubleConsumer wherein the parameterized DoubleConsumer will be executed after the first one. If the evaluation of either operation throws an error, it is relayed to the caller of the composed operation.
Note: The operation being passed as the argument should be of type DoubleConsumer .
Syntax:
default DoubleConsumer andThen(DoubleConsumer after)
Parameters: This method accepts a parameter after which is the DoubleConsumer to be applied after the current one.
Return Value: This method returns a composed DoubleConsumer that first applies the current operation first and then the after operation.
Exception: This method throws NullPointerException if the after operation is null.
Below is the code to illustrate andThen() method:
Program 1:
import java.util.function.DoubleConsumer;  public class GFG {    public static void main(String args[])    {          // Create a DoubleConsimer Instance        DoubleConsumer display = a -> System.out.println(a * 10);        DoubleConsumer mul = a -> a /= 2;          // using addThen() method        DoubleConsumer composite = mul.andThen(display);        composite.accept(3);    }}
30.0

Program 2: To demonstrate when NullPointerException is returned.
import java.util.function.DoubleConsumer;  public class GFG {    public static void main(String args[])    {          // Create a DoubleConsimer Instance        DoubleConsumer mul = a -> a /= 10;          try {              // using addThen() method            DoubleConsumer composite = mul.andThen(null);              composite.accept(3);        }        catch (Exception e) {            System.out.println("Exception : " + e);        }    }}
Exception : java.lang.NullPointerException

Program 3: To demonstrate how an Exception in the after function is returned and handled.
import java.util.function.DoubleConsumer;  public class GFG {    public static void main(String args[])    {          try {              DoubleConsumer                conv                = a                -> System.out.println(                    Integer                        .parseInt(                            Double                                .toString(a)));            DoubleConsumer mul = a -> a /= 10;              // using addThen() method            DoubleConsumer composite = mul.andThen(conv);              composite.accept(3);        }        catch (Exception e) {            System.out.println("Exception : " + e);        }    }}
Exception : java.lang.NumberFormatException: For input string: "3.0"

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