higher-order what?
Higher-order means that it is possible to pass to a method both values and functions and in the same way the method itself can return either a value or a function.
Example:
• public void doSomething(String name, Function someFunction){...}
• public Function createAnAction(Integer someInteger)
EASY!!!!
Use case 1:
Print a message with weight information in kilos.
This is easy :
package com.marco.higherOrder;
public class Printer {
public void print(int weight) {
System.out.println("Printing : your weight is " + weight + " kilos");
}
public static void main(String[] args) {
Printer printer = new Printer();
printer.print(65);
}
}
Use case 2:
I need to be able to print different weight unit like stone and pounds.
Ok, just put an if and shut up!!
Putting an if it means to add and pass a boolean and then check that boolean and put a boring if/else.
Also what about open close principle? what if we need to add yet another weight unit?
Higher-order Function to the rescue:
I want a class in charge of handling different weight units :
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package com.marco.higherOrder;
public class Scale {
public String toStones(int weight) {
return "your weight is " + weight + " stones";
}
public String toKilos(int weight) {
return "the weight is " + weight + " kilos";
}
public String toPounds(int weight) {
return "the weight is " + weight + " pounds";
}
}
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Then I can add a Function in my Printer.print method and pass functions:
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package com.marco.higherOrder;
import java.util.function.Function;
public class Printer {
public void print(int weight, Function<Integer, String> scale) {
System.out.println("Printing : " + scale.apply(weight));
}
public static void main(String[] args) {
Printer sender = new Printer();
Scale scale = new Scale();
sender.print(65, scale::toKilos);
sender.print(65, scale::toStones);
sender.print(65, scale::toPounds);
}
}
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Function<Integer, String> means that this function will accept an Integer and will return a String.
scale::toKilos means that the method toKilos of the scale instance will be called.
EASY!!!!
What if I don't need the Scale class?
Then don't don't it :)!!!
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package com.marco.higherOrder;
import java.util.function.Function;
public class Printer {
public void print(int weight, Function<Integer, String> scale) {
System.out.println("Printing : " + scale.apply(weight));
}
public static void main(String[] args) {
Printer sender = new Printer();
sender.print(65, p -> "your weight is " + p + " kilos");
sender.print(65, p -> "your weight is " + p + " stones");
sender.print(65, p -> "your weight is " + p + " pounds");
}
}
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p -> "your weight is " + p + " kilos" the p is simply the int that will be passed to the method.
Functional it’s easy , don’t trust who says it’s hard!
Have a great weekend
Ciao.
