import java.util.*;
import java.lang.*;
import java.io.*;
 
class TestClass {
 
	@FunctionalInterface
	public interface ToDoubleFunction<T extends TestClass, U extends Number> {
		Double applyAsDouble(T classInstance, U value);
	}
 
	<U extends Number> Double getDouble(U value) {
		System.out.println(this);
 
        return value.doubleValue();
    }
 
	public static void main (String[] args) throws java.lang.Exception
	{
		ToDoubleFunction<TestClass, Long> tdf = TestClass::getDouble;
 
		TestClass c = new TestClass();
 
		System.out.println(c);
 
		System.out.println(tdf.applyAsDouble(c, new Long(43)));
	}
}

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