Libraries - Java 8 Lambdas - page 48

A BinaryOperator is special type of BiFunction for which the arguments and the return
type are all the same. For example, adding two integers would be a BinaryOperator .

Because lambda expressions have the types of their functional interfaces, the same rules ap-
ply when passing them as arguments. We can overload a method with the BinaryOperator
and an interface that extends it. When calling these methods, Java will infer the type of your
lambda to be the most specific functional interface. For example, the code in Example 4-7
prints out IntegerBinaryOperator when choosing between the two methods in
Example 4-8 .

Example 4-7. Another overloaded method call
overloadedMethod (( x , y ) -> x + y );

Example 4-8. A choice between two overloaded methods
private private interface interface IntegerBiFunction IntegerBiFunction extends extends BinaryOperator < Integer > {

}

private private void void overloadedMethod ( BinaryOperator < Integer > lambda ) {

System . out . print ( "BinaryOperator" );

}

private private void void overloadedMethod ( IntegerBiFunction lambda ) {

System . out . print ( "IntegerBinaryOperator" );

}

Of course, when there are multiple method overloads, there isn't always a clear “most specif-
ic type.” Take a look at Example 4-9 .

Example 4-9. A compile failure due to overloaded methods
overloadedMethod (( x ) -> true true );

private private interface interface IntPredicate IntPredicate {

public public boolean boolean test ( int int value );

}

private private void void overloadedMethod ( Predicate < Integer > predicate ) {

System . out . print ( "Predicate" );

}

private private void void overloadedMethod ( IntPredicate predicate ) {

System . out . print ( "IntPredicate" );

}