functional programming - Composing Function interfaces in Java -

interface pairfloatfunction {    pair<float,float> calculate(int x); }  interface floatfunction {    float calculate(int x); }  class sqrt implements pairfloatfunction {    public pair<float, float> calculate(int x) {       return new pair(-pow(x,0.5), pow(x,0.5))    }  }  class add_one implements floatfunction {    public float calculate(int x) {       return x + 1;    } } 

i compose functions can perfom this:

add_one(sqrt(100)) = pair(-9,11) 

i understand need 'glue' functions together. stuck here, should writing method overload this?

class add_one {    public float calculate(int x) {       return x + 1;    }    public float calculate(pair pair) {      pair.first += 1;      pair.second += 1;      return pair    } } 

sorry new functional programming, there nice solution this?

based on code above, create generic interface responsible calculating.

interface calculation<t> {     t calculate(int x); } 

this java 7 implementation, because did not specify java 8.

further explanation

the return type t generic; meaning implementation can return object type must consume integer x. make x parameter generic can decide function take parameter type.

note: static classes moved own class files , static modifier should removed. did consolidate sake of brevity.

full example

public class functional {     static interface calculation<t> {         t calculate(int x);     }      static class sqrt implements calculation<pair<float, float>> {         public pair<float, float> calculate(int x) {             float root = (float) math.pow(x, 0.5);             return new pair<float, float>(-root, +root);         }     }      static class addone implements calculation<float> {         public float calculate(int x) {             return (float) (x + 1);         }     }      static <t> t calculate(int x, calculation<t> calculation) {         return calculation.calculate(x);     }      public static void main(string[] args) {         calculation<?>[] calculations = { new sqrt(), new addone() };         int x = 49;          (calculation<?> calculation : calculations) {             system.out.printf("%s: %s%n",                     calculation.getclass().getsimplename(),                     calculate(x, calculation));         }     }      static class pair<t, u> {         private t val1;         private u val2;          public pair(t val1, u val2) {             this.val1 = val1;             this.val2 = val2;         }          protected t getval1() {             return val1;         }          protected void setval1(t val1) {             this.val1 = val1;         }          protected u getval2() {             return val2;         }          protected void setval2(u val2) {             this.val2 = val2;         }          @override         public string tostring() {             return "(" + val1 + ", " + val2 + ")";         }     } } 

output

sqrt: (-7.0, 7.0) addone: 50.0