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9.4 Higher Order Functions in Java

Higher Order Function: A function that treats another function as data.
  • e.g. takes a function as input.
  • Example in Python:
def tenX(x):
return 10*x
def do_twice(f, x):
return f(f(x))
print(do_twice(tenX, 2))

Higher Order Functions in Java 7

Old School (Java 7 and earlier)
  • Fundamental issue: Memory boxes (variables) cannot contain pointers to functions.
    • use an interface instead:
public interface IntUnaryFunction {
int apply(int x);
}
public class TenX implements IntUnaryFunction {
public int apply(int x) {
return 10 * x;
}
}
This code above is the same as the Python code:
def tenX(x):
return 10*x
Now, to finish the rest of the Python code in Java:
public interface IntUnaryFunction {
int apply(int x);
}
public class TenX implements IntUnaryFunction {
public int apply(int x) {
return 10 * x;
}
}
public class HoFDemo {
public static int do_twice(IntUnaryFunction f, int x) {
return f.apply(f.apply(x));
}
public static void main(String[] args) {
System.out.println(do_twice(new TenX(), 2));
}
}
This code above is equivalent to the Python code provided earlier.