passing a function pointer to a method - function

Question

I've read some posts about function pointers but I still don't understand how to use 'function pointers' the best for my case. Also in this case It isn't clear to me the use of anonymous classes...
Here the code:
class Fitness {
private List < Double > list;
interface Foo {
//public Foo;
Object myFunc(Object arg);
Object myFunc2(Object arg);
}
public Fitness(List < Double > list) {
this.list = new ArrayList < Double > (list);
}
public void bar(Foo foo) {
Object object = foo.myFunc(list);
System.out.println(object);
Object object2 = foo.myFunc2(list);
System.out.println(object2);
}
public void method(String func) {
if (func.equals("f1"))
bar(
new Foo() {
public Object myFunc(Object arg) {
return (Double)((List) arg).get(0) + 50.0;
}
public Object myFunc2(Object arg) {
return (Double)((List) arg).get(0) + 50.0;
}
});
else if (func.equals("f2"))
bar(
new Foo() {
public Object myFunc(Object arg) {
List < Double > l = (List < Double > ) arg;
return l.get(0) / l.size();
}
public Object myFunc2(Object arg) {
List < Double > l = (List < Double > ) arg;
return l.get(0) / l.size();
}
});
}
public void fitness1() {
bar(
new Foo() {
public Object myFunc(Object arg) {
return (Double)((List) arg).get(0) + 50.0 * 1000;
}
public Object myFunc2(Object arg) {
return (Double)((List) arg).get(0) + 50.0;
}
});
}
}
class Example {
public static void main(String[] args) {
ArrayList < Double > listD = new ArrayList < Double > ();
listD.add(100.0);
listD.add(-1.0);
listD.add(-5.0);
Fitness t = new Fitness(listD);
//t.method("f1");
//t.method("f2");
//t.method2();
t.fitness1();
}
}
What I would like is an object Fitness that call a fitness function according to some parameters. A fitness method should be able to take a list of int, double, even couple <int, String>.
I want to do a test: so I want to see the different results if I choose f1, f2, f3, f4. I am confused about how to code it.
Thanks in advance

Answer 1

You can declare the following interface:
interface FooFunc {
Object invoke(Foo foo, Object arg);
}
Then change slightly your bar() method:
public void bar(Foo foo, FooFunc func) {
Object object = func.invoke(foo, list);
System.out.println(object);
}
... and your fitness1() method:
public void fitness1(FooFunc func) {
bar(
new Foo() {
public Object myFunc(Object arg) {
return (Double) ((List) arg).get(0) + 50.0 * 1000;
}
public Object myFunc2(Object arg) {
return (Double) ((List) arg).get(0) + 50.0;
}
}, func);
}
Now, from your main() method, you can do:
Fitness t = new Fitness(listD);
t.fitness1(Fitness.Foo::myFunc);
t.fitness1(Fitness.Foo::myFunc2);
Isn't it great?
UPDATE: Complete file
import java.util.ArrayList;
import java.util.List;
class Fitness {
private List<Double> list;
interface Foo {
//public Foo;
Object myFunc(Object arg);
Object myFunc2(Object arg);
}
interface FooFunc {
Object invoke(Foo foo, Object arg);
}
public Fitness(List<Double> list) {
this.list = new ArrayList<Double>(list);
}
public void bar(Foo foo, FooFunc func) {
Object object = func.invoke(foo, list);
System.out.println(object);
}
public void fitness1(FooFunc func) {
bar(
new Foo() {
public Object myFunc(Object arg) {
return (Double) ((List) arg).get(0) + 50.0 * 1000;
}
public Object myFunc2(Object arg) {
return (Double) ((List) arg).get(0) + 50.0;
}
}, func);
}
}
public class Example {
public static void main(String[] args) {
ArrayList<Double> listD = new ArrayList<>();
listD.add(100.0);
listD.add(-1.0);
listD.add(-5.0);
Fitness t = new Fitness(listD);
t.fitness1(Fitness.Foo::myFunc);
t.fitness1(Fitness.Foo::myFunc2);
}
}