What is the OptionalLong.orElseThrow method in Java?

Overview

In Java, the OptionalInt object is a container object that may or may not contain an integer value.

The OptionalInt class is present in the java.util package.

The `orElseThrow()` method

The orElseThrow method returns the long value present in the OptionalLong object.

If the value is not present, then the supplier function passed as an argument is executed and an exception is returned on the function that is thrown.

Syntax

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

Parameters

The orElseThrow method accepts the function to be executed if the OptionalLong object is empty (no value present in the Optional object) as an argument.

The supplier function should return the exception to be thrown.

Return value

If the OptionalLong object contains a value, then the method returns the value. Otherwise, orElsethrow returns the exception returned by the supplier function.

This method throws NullPointerException if no value is present and the supplier function is null.

Code

The code below denotes how to use the orElseThrow method.

import java.util.OptionalLong;
  
class OptionalLongOrElseThrowExample {
    public static void main(String[] args) throws Exception{
        OptionalLong optional1 = OptionalLong.of(1);
        System.out.println("Optional1 : " + optional1);
        long val =  optional1.orElseThrow(()-> {
                return new Exception("no value present in Optional object"); 
            });
        System.out.println("Value at Optional1 is : " + val);
        OptionalLong optional2 = OptionalLong.empty();
        System.out.println("\nOptional2 : " + optional2);
        val =  optional2.orElseThrow(()-> {
                return new Exception("no value present in Optional object");
            });
    }
}

Explanation

In the code above:

Line 1: We import the OptionalLong class.
```
import java.util.OptionalLong;
```
Line 5: We use the of method to create an OptionalLong object with value 1.
```
OptionalLong optional1 = OptionalLong.of(1);
```
Line 7: We call the orElseThrow method on the optional1 object.

For the orElseThrow method, a supplier function that returns an Exception object is passed as an argument.

This method returns 1 because the optional1 object contains the value.
```
long val =  
optional1.orElseThrow(()-> { 
  return new Exception("no value present in Optional object"); 
});
```
Line 12: We use the empty method to get an empty OptionalLong object. The returned object doesn’t have any value.
```
OptionalLong optional2 = OptionalLong.empty();
```
Line 14: We call the orElseThrow method on the optional2 object.

For the orElseThrow method, a supplier function that returns an Exception object is passed as an argument.

This method throws the exception returned by the supplier function because the optional2 object doesn’t have a value.
```
val = optional2.orElseThrow(()-> { 
  return new Exception("no value present in Optional object"); 
});
// exception is thrown 
```

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