Optional orElseThrow() method in Java with examples

The orElseThrow() method of java.util.Optional class in Java is used to get the value of this Optional instance if present. If there is no value present in this Optional instance, then this method throws the exception generated from the specified supplier.

Syntax:

public <X> T
  orElseThrow(Supplier<X> exceptionSupplier)
  throws X extends Throwable

Parameters: This method accepts supplier as a parameter of type X to throws an exception if there is no value present in this Optional instance.

Return supplier: This method returns the value of this Optional instance, if present. If there is no value present in this Optional instance, then this method throws the exception generated from the specified supplier.

Exception: This method throws NullPointerException if there is no value present in this Optional instance.

Below programs illustrate orElseThrow() method:
Program 1:

// Java program to demonstrate
// Optional.orElseThrow() method

import java.util.*;
import java.util.function.*;

public class GFG {

    public static void main(String[] args)
    {

        // create a Optional
        Optional<Integer> op
            = Optional.of(9455);

        // print supplier
        System.out.println("Optional: "
                           + op);

        // orElseThrow supplier
        System.out.println(
            "Value by orElseThrow("
            + "ArithmeticException::new) method: "
            + op.orElseThrow(
                  ArithmeticException::new));
    }
}

Output:

Optional: Optional[9455]
Value by orElseThrow(ArithmeticException::new) method: 9455

Program 2:

// Java program to demonstrate
// Optional.orElseThrow() method

import java.util.*;
import java.util.function.*;

public class GFG {

    public static void main(String[] args)
    {

        // create a Optional
        Optional<Integer> op
            = Optional.empty();

        // print supplier
        System.out.println("Optional: "
                           + op);

        try {

            // orElseThrow supplier
            System.out.println(
                "Value by orElseThrow("
                + "ArithmeticException::new) method: "
                + op.orElseThrow(
                      ArithmeticException::new));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

Optional: Optional.empty
java.lang.ArithmeticException

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Optional.html#orElseThrow-java.util.function.Supplier-