Lambda Expression
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Lambda expressions allow passing functions as arguments. This document discusses two approaches to filtering a list of Person objects by criteria using lambda expressions. The first approach defines a PersonCriteria interface to test Person objects. A service class uses the criteria to filter and print matching persons. The second approach uses lambda expressions with stream aggregate operations like filter and map to directly operate on the person list.
![Approach 1 : Compare the object on various
criterias.
Create a service class
public class PersonFilterService {
public void printPerson(List<Person> persons,PersonCriteria
pc ){
for(Person p : persons){
if(pc.testPerson(p))
System.out.println("Name :"+p.getName());
}
}
}
Create class to get filtered Person objects
public static void main (String args[]){
Person p1 = new Person("Sumit", "female", 34, "Gurgaon",
"Haryana");
Person p2 = new Person("Niren", "male", 40, "Gurgaon",
"Haryana");](https://image.slidesharecdn.com/lambda-161215180450/85/Lambda-Expression-4-320.jpg)
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Lambda Expression
- 1. LambdaExpression What is Lambda Expression? Lambda expression is a functional programming where functionality or function implementation is passed as an argument. *Functional programming: In this technique pure logic is executed without changing the Object state.
- 2. Why or when to use Lambda? Approach 1 : Compare the object on various criterias. Example : Person with attributes<Name, Age, Gender, City, State> Problem Stmt :Filter List of Person for various criterias as follows Get all female persons. All persons having age greater than 30. List all Persons who belong to one city. In this we can have different solutions possible as creating seperate methods for each condition. Or one generic method
- 3. Approach 1 : Compare the object on various criterias. Create Class public class Person { private String name; private String gender; private Integer age; private String city; private String state; } Create criteria interface public interface PersonCriteria { boolean testPerson(Person p); } This class is responsible to adding the filter
- 4. Approach 1 : Compare the object on various criterias. Create a service class public class PersonFilterService { public void printPerson(List<Person> persons,PersonCriteria pc ){ for(Person p : persons){ if(pc.testPerson(p)) System.out.println("Name :"+p.getName()); } } } Create class to get filtered Person objects public static void main (String args[]){ Person p1 = new Person("Sumit", "female", 34, "Gurgaon", "Haryana"); Person p2 = new Person("Niren", "male", 40, "Gurgaon", "Haryana");
- 5. Approach 2: Performaing operations on the elements using Aggregate Operations. To print elements of an array. Use Aggregate Operations that Accept Lambda Expressions as Parameters. Example : Print the name of persons who have gender Female. persons.stream().filter((Person p)- >p.getGender().equals("female")).map(p->p.getName() ).forEach(name -> System.out.println(name));