Supplier interface in Java

A Supplier is a simple interface which indicates that this implementation is a supplier of results. This interface, however, does not enforce any restrictions that supplier implementation needs to return a different result on each invocation.
The supplier has only one method get() and does not have any other default and static methods.
```
import java.util.function.DoubleSupplier;
import java.util.function.Supplier;

public class Main {
    public static void main(String[] args) {
        Supplier<Double> doubleSupplier1 = () -> Math.random();
        DoubleSupplier doubleSupplier2 = Math::random;

        System.out.println(doubleSupplier1.get());
        System.out.println(doubleSupplier2.getAsDouble());
    }
}
```
One of the primary usage of this interface to enable deferred execution. This means delaying the execution until it is needed. For example, Optional class has a method named orElseGet. This method is triggered if optional does not have data. This is demonstrated below:
```
import java.util.Optional;
import java.util.function.Supplier;

public class Main {
    public static void main(String[] args) {
        Supplier<Double> doubleSupplier = () -> Math.random();
        Optional<Double> optionalDouble = Optional.empty();
        System.out.println(optionalDouble.orElseGet(doubleSupplier));
    }
}
```
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