Can i use Lambda Expression in jdk8，Implement a generic function to calculate way

Question

Like this

1.f(x,y)=ax+by
2.f(x,y,z)= ax+by+cz
3.f(2x,2y) = ax^2+by^2 
....
4.f(2x,y,3z,4m,5n) = ax^2+by+cz^3+dm^4+en^5

My idea is as follows this java method named myFun()()()

1.myFun(x,y)(1,2)(3,4) = x+2y = 3+8 = 11
2.myFun(x,y)(1,2,3)(1,1,1) = x+2y+3z = 1+2+3=6
....

I konw Y combination operator,and Currying，but i don't know how to use in java，If can't, I can do it in python?

What do you mean by `f(2x,2y)` and `f(2x+y+3z+4m+5n)`? Particularly the latter: that only has a single input, so how can it know the values of `x`, `y`, `z` etc distinctly? — Andy Turner, Jun 21 '22 at 09:00
`myFun(x,y)(1,2)(3,4)` - in Java, this code has no sense at all. I guess it would be better to start with a basic [tutorial on lambda expressions](https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html) and, firstly, on [language basics](https://docs.oracle.com/javase/tutorial/java/index.html). If you hope to learn a new language by trying to reproduce your experience in another language (without reading books, documentation, etc.) that would not work. — Alexander Ivanchenko, Jun 21 '22 at 09:08

score 1 · Answer 1 · answered Jun 21 '22 at 12:20

Try this.

interface F { double apply(double x, double y); }
interface G { F apply(double a, double b); }

G myFunc = (a, b) -> (x, y) -> a * x + b * y;
System.out.println(myFunc.apply(1, 2).apply(3, 4));

output:

11.0

WJS · Answer 2 · 2022-06-21T13:39:36.730

I believe this is what you want.

create a BiFunction that returns a lambda which takes x and y and applies the subsequent lambda to xx and yy.

BiFunction<Integer,Integer, IntBinaryOperator> fn1 = (x,y)-> (xx,yy)-> x*xx + y*yy;
int result = fn1.apply(1,2).applyAsInt(3,4);
System.out.println(result);

prints

Both the BiFunction and IntBinaryOperator are Functional interfaces in the java.util.function package. To use more variables, one has to define new functional interfaces.


interface TriFunction<S,T,U,V> {
    V apply(S arg1, T arg2, U arg3);
}

interface IntTrinaryOperator {
    int applyAsInt(int ar1,int arg2, int arg3);
}

Then declare the result as before.


TriFunction<Integer,Integer, Integer,IntTrinaryOperator> fn2 = (x,y,z)-> (xx,yy,zz)-> x*xx + y*yy + z*zz;
int result2 = fn2.apply(1,2,3).applyAsInt(1,1,1);
System.out.println(result2);

prints

Update

As long as you are using primitive types as the arguments you can use the ... notation to allow different number of arguments.

interface IntNaryOperator {
    int applyAsInt(int...a);
}

interface NFunction<R> {
    R apply(int...s);
}

NFunction<IntNaryOperator> fn3 = (int[] a)->(int[] b)-> {
                  
                  int sum = 0;
                  for (int i = 0;i < a.length; i++) {
                      sum += (a[i]*b[i]);
                  }
                  return sum;
};

int sum  = fn3.apply(1,2,3,4,5,6,7).applyAsInt(1,2,3,4,5,6,7);
System.out.println(sum);

prints

If generic arrays are used it is possible to pollute the heap. The method names can of course be changed to whatever makes sense for you. And you may want to verify that the supplied argument counts are the same or you could get an ArrayIndexOutOfBoundsException.

Can i use Lambda Expression in jdk8，Implement a generic function to calculate way

2 Answers2