Java8 Lambda Expression
In this article, we will discuss Java8 most debated feature Lambda Expression.
What is a Lambda Expression?
In brief, I can say Lambda Expression is the way of passing functions into a function. Where Passing function is being used by the function where it passed.
Passing function act as a Callback function.
In Java 8 Version Java adopts the Lambda expression actually this is the first step towards functional programming. In functional programming, we can pass a function in another function that is called Higher Order Function.
The benefits of this are Lambda Expression is
As you can pass a function into an another function or I can say you can pass behavior into a function (think function as a behavior). So It is on caller's hand what behavior you can want to do or I can say the strategy is on caller’s hand so it can be altered easily. Prior to this If you want to pass a behavior probably you will create an anonymous class and wrap that behavior in that class and pass it to the another method.
To be specific prior to Lambda expression we will solve this problem that is passing behavior into a method by anonymous class.
Think about Thread and Runnable interface. In Runnable interface there is a run method where we define the behavior or the set activities which should be executed when a thread is spawned.
And we pass this in Thread constructor so when Thread is in running state it performs the activity written in Runnable. But to do we have to create an anonymous class and override public void run then pass it in Thread class.
This not right way to pass a function rather what we did we pass an object where the function is in wrapped form.
Java8 try to get rid of this now no need to create that class directly you can pass a method body to a method.
Let’s take an Example
Suppose I need to compute an Area of Circle and Rectangle and print them so How to do it by lambda Expression.
First I create two functional interfaces, It just a Java interface and it has one method where I specify the behavior template method.
package com.example.java;
public interface Shape {
public int execute(int a,int b);
}
package com.example.java;
public interface Print {
public void print(int value);
}
Now I create a Class where we define Rectangle and Circle compute behavior and print behavior by Lambda Expression
package com.example.impl;
import com.example.java.Print;
import com.example.java.Shape;
public class ShapeClosure {
public void computeArea(Shape shape,Print print,int length,int breadth)
{
int result = shape.execute(length, breadth);
print.print(result);
}
public static void main(String[] args) {
ShapeClosure closure = new ShapeClosure();
Shape circle = (a,b)->(int)3.14f*a*b;
Print area = (result)->System.out.println("Area of Circle " + result);
closure.computeArea((a,b)->a*b, (result)->System.out.println("Area of Rectangle " + result), 10, 20);
closure.computeArea(circle, area, 10, 5);
}
}
Look at the ShapeClosure class here I create a ComputeArea Function, the function which will take Shape and Print function as a callback function. In order to do that
Look at the ComputeArea function arguments, it takes shape and Prints functional interface as the argument. Because this functional interface says about the behavior of the function
Shape interface behavior is executed which takes two int argument and return an int
Print interface behavior is print which takes an int argument and prints the value.
In computing are we call this behavior or another way I can say in a function I use callback function's behavior which is the main motto of functional programming
Now look these lines in the main method
Shape circle = (a,b)->(int)3.14f*a*b;
Print area = (result)->System.out.println("Area of Circle " + result);
closure.computeArea((a,b)->a*b, (result)->System.out.println("Area of Rectangle " + result), 10, 20);
closure.computeArea(circle, area, 10, 5);
Here I use Lambda expression as shape’s execute method takes two int’s and compute them so
(a,b)->(int)3.14f*a*b;
Two arguments int a and b (Don’t need to say data type from functional interface java takes the argument type.)
Now define the body of executing as (int)3.14f*a*b;
So these line is (a,b)->(int)3.14f*a*b;
Is equivalent to
public int execute(int a,int b)
{
return (int)3.14f*a*b;
}
Same for print , I pass them in computeArea along with data’s which is main intent of functional programming
closure.computeArea(circle, area, 10, 5);
On another way, I can directly pass them in computeArea like this
closure.computeArea((a,b)->a*b, (result)->System.out.println("Area of Rectangle " + result), 10, 20);
when you run the program. You will see Output
Area of Rectangle 200
Area of Circle 150
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