Recall callbacks.

Passing Functions

• Another Example
• Customize Arrays.sort → This is an already available static method.
• We customize in order to tell this function how to compare two objects of any type → Through an interface.
• Comparator interface provides signature for comparison function.
• Implement Comparator and Pass to Arrays.sort

public interface Comparator<T> {
	public abstract int compare(T o1, T o2);
}

public class StringCompare implements Comparator<String>{
	public int compare(String s1, String s2){
		return s1.length() - s2.length();
	}
}

String[] strarr = new ... ;
Arrays.sort(starr,StringCompare);

Functional Interfaces

<aside> 💡 Interfaces that define a single function are called Functional Interfaces.

</aside>

Examples: Comparator, Timerowner (in callback).

• Since these interfaces have only one function in them, and we are creating an object of these interfaces just to use that one function, is there some way to directly pass this function, instead of wrapping them inside an interface?

• Functional interface can be visualized as a box carrying just one function. Instead of passing the box onto the next person, can we just pass the function itself, since it is guaranteed to only have one function?

• In Python, function names are similar to variable names.

  • Define a function.
  • Pass it as an argument to another function.
  • map is a higher order function. ( Simply a function which takes another function as its argument)

  def square(x):
  	return x*x
  l = list(map(square,range(100)))
  

• How to do this in Java → Lambda Expressions.

Lambda Expressions

<aside> 💡 Lambda expressions denote anonymous functions.

</aside>

• ( Parameters ) -> Body
• Return value and type are implicit.