Java Lambda - Java Intersection Type

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Java 8 introduced a new type called an intersection type

An intersection type is an intersection of multiple types.

An intersection type may appear as the target type in a cast.

An ampersand is used between two types as Type1 & Type2 to represent a new type that is an intersection of Type1, Type2.

Example

The following code uses a cast with an intersection type that creates a new synthetic type that is a subtype of all types.

It creates two interfaces, Calculator is a functional interface and can be used with lambda expression. The other is called NonFunction which is not a functional interface. In order to create a lambda expression and assign to NonFunction we use the & to create a new subtype.

The intersection type NonFunction & Calculator is a functional interface.

public class Main {
  public static void main(String[] argv) {
    //  w w  w. j  a  v a 2s .  c  o  m
    NonFunction nonFunction = (NonFunction & Calculator) (x,y)-> x + y;
  }  
}

@FunctionalInterface
interface Calculator{
  long calculate(long x, long y);
}

interface  NonFunction{
}

Example 2

The following code creates an intersection type by intersecting java.io.Serializable marker interface with our own functional interface.

public class Main {
  public static void main(String[] argv) {
    /*from   w ww.j a v  a 2  s  .com*/
    java.io.Serializable ser = (java.io.Serializable & Calculator) (x,y)-> x + y;
  }  
}

@FunctionalInterface
interface Calculator{
  long calculate(long x, long y);
}

In this way we make a lambda expression serializable.

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