LambdaInference.java

package streams;

import java.util.function.*;

public class LambdaInference {

	@SuppressWarnings("unused")
	public static void main(String[] args) {
		
		// *** Part 1: identify the FI

		// Standard syntax
		Consumer<String> c1 = msg -> System.out.println(msg.length());
		
		
		// Compile-time error: not enough info
		// Object x1 = msg -> System.out.println(msg.length());
				
		
		// Compile-time error: not enough info
		// Object x2 = (String msg) -> System.out.println(msg.length());
		
		
		// OK: cast added
		Object x3 = (Consumer<String>) ((String msg) -> System.out.println(msg.length()));

		
		
		
		
		
		
		
		
		
		
		
		
		
		// *** Part 2: identify parameter types

		
		// OK: but inferred parameter type is Object
		Consumer<?> c2 = msg -> System.out.println(msg);
		
		
		// Compile-time error: Inference is *not* based on body of lambda
		// Consumer<?> c3 = msg -> System.out.println(msg.length());
		
		
		// OK: added manifest type to parameter
		Consumer<?> c4 = (String msg) -> System.out.println(msg.length());
	}
	
	

	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	public static <T extends Employee> T testWithNull(UnaryOperator<T> transformer) {
		return transformer.apply(null);
	}
	
	
	public static void main2() {		

		// *** Part 2: on the parameter type of lambdas
		
		// Doubles the bonus of a Manager
		UnaryOperator<Manager> doubleBonus = manager ->
			new Manager(manager.getName(), manager.getSalary(), 2*manager.getBonus());

		
			
		Manager test1 = testWithNull(doubleBonus);

		
		Manager test2 = testWithNull(manager ->
			new Manager(manager.getName(), manager.getSalary(), 2*manager.getBonus()));

		
		// Compile-time error: Inference is not based on body of lambda
		// Employee test3 = testWithNull(manager ->
		// 	new Manager(manager.getName(), manager.getSalary(), 2*manager.getBonus()));
				
		
	}

}