Java 8 Streams

RajeshAbhimanyu — Tue, 11 Feb 2020 12:06:00 +0000

Streams are very basic in java 8 features . Below is my example where I'm going to cover different API methods .

public class StreamBuilders {

 public static void main(String[] args){
     List<Integer> list = new ArrayList<Integer>();
     for(int i = 1; i< 10; i++){
         list.add(i);
     }
     Stream<Integer> stream = list.stream();
     // stream count 
        long count=list.stream().count();
    //limit 
        System.out.println("fileter value :"+   list.stream().filter(i->i>5).count());
        System.out.println("count is "+count);
     List<Integer> evenNumbersList = stream.filter(i -> i%2 == 0).collect(Collectors.toList());
     System.out.print(evenNumbersList);
    // filter operations 
    List<String> nameList = Arrays.asList("Ram", "Amit", "Ashok", "Manish", "Rajat");
    nameList.stream().filter(n->n.startsWith("A")).collect(Collectors.toList()).forEach(System.out::println);

    nameList.stream().filter(n -> !n.startsWith("A")).collect(Collectors.toList()).forEach(System.out::println);
//map
list.stream().map(n->n*2).filter(n->n>10).forEach(System.out::println);

//complex operations
List<Person> persons =
Arrays.asList(
    new Person("Max", 18,"10000","computers"),
    new Person("Peter", 23,"15000","maths"),
    new Person("Pamela", 23,"17000","computers"),
    new Person("David", 12,"10000","physics"));

// grouping the objects with age

List<Person>p1= persons.stream().filter(n->n.name.startsWith("P")).collect(Collectors.toList());
System.out.println(p1);
Map<Integer,List<Person>> personWithGroupBy=persons.stream().collect(Collectors.groupingBy(p->p.age));
personWithGroupBy.forEach((age,p)->System.out.format("age %s: %s\n", age, p));

//grouping the persons with department

Map<String,List<Person>> personsWithGroupByDept=persons.stream().collect(Collectors.groupingBy(Person::getDept));
personsWithGroupByDept.forEach((dept,p)->System.out.println(" dept : "+dept+"  "+p));

// grouping the persons with salary
Map> personWithSalary= persons.stream().collect(Collectors.groupingBy(p->p.salary));
personWithSalary.forEach((salary,p)->System.out.println("salary :"+salary+" "+p));

Map> personWithDept=persons.stream().collect(Collectors.groupingBy(p->p.dept));
personWithDept.forEach((dept,p)->System.out.println("dept : "+dept+ " "+p));

//sorting persons based on person name

persons.sort(Comparator.comparing(p->p.name));
    System.out.println("sorted list "+persons);
persons.sort(Comparator.comparing(p->p.dept));
System.out.println("sorted with dept "+persons);

  }

}

class Person {
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getSalary() {
return salary;
}
public void setSalary(String salary) {
this.salary = salary;
}
public String getDept() {
return dept;
}
public void setDept(String dept) {
this.dept = dept;
}
String name;
int age;
String salary;
String dept;

Person(String name, int age,String salary,String dept) {
    this.name = name;
    this.age = age;
    this.salary=salary;
    this.dept=dept;
}

@Override
public String toString() {
    return name +" "+salary+" " +dept+" "+age;
}

}

out put :
c:\rajesh\MicroServices\Java8Practice>java StreamBuilders
fileter value :4
count is 9
[2, 4, 6, 8]Amit
Ashok
Ram
Manish
Rajat
12
14
16
18
[Peter 15000 maths 23, Pamela 17000 computers 23]
age 18: [Max 10000 computers 18]
age 23: [Peter 15000 maths 23, Pamela 17000 computers 23]
age 12: [David 10000 physics 12]
dept : maths [Peter 15000 maths 23]
dept : physics [David 10000 physics 12]
dept : computers [Max 10000 computers 18, Pamela 17000 computers 23]
salary :17000 [Pamela 17000 computers 23]
salary :15000 [Peter 15000 maths 23]
salary :10000 [Max 10000 computers 18, David 10000 physics 12]
dept : maths [Peter 15000 maths 23]
dept : physics [David 10000 physics 12]
dept : computers [Max 10000 computers 18, Pamela 17000 computers 23]
sorted list [David 10000 physics 12, Max 10000 computers 18, Pamela 17000 computers 23, Peter 15000 maths 23]
sorted with dept [Max 10000 computers 18, Pamela 17000 computers 23, Peter 15000 maths 23, David 10000 physics 12]

Forem: RajeshAbhimanyu

Java 8 Streams