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Java 8 Stream Filter examples

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Java 8 Stream Filter examples

Java 8 Stream API is very useful for filtering collections. Lets see example of java 8 filter API
Scenario
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class TempStudent {
    public String name;
    public int age;
    public Address address;
    public List<MobileNumber> mobileNumbers;
 
    public TempStudent(String name, int age, Address address, List<MobileNumber> mobileNumbers) {
        this.name = name;
        this.age = age;
        this.address = address;
        this.mobileNumbers = mobileNumbers;
    }
}
 
class Student{
    private String name;
    private int age;
    private Address address;
    private List<MobileNumber> mobileNumbers;
 
    public Student(String name, int age, Address address, List<MobileNumber> mobileNumbers) {
        this.name = name;
        this.age = age;
        this.address = address;
        this.mobileNumbers = mobileNumbers;
    }
 
    public String getName() {
        return name;
    }
 
    public int getAge() {
        return age;
    }
 
    public Address getAddress() {
        return address;
    }
 
    public List<MobileNumber> getMobileNumbers() {
        return mobileNumbers;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public void setAddress(Address address) {
        this.address = address;
    }
 
    public void setMobileNumbers(List<MobileNumber> mobileNumbers) {
        this.mobileNumbers = mobileNumbers;
    }
 
    @Override
    public String toString() {
        return "Student{" +
            "name='" + name + '\'' +
            ", age=" + age +
            ", address=" + address +
            ", mobileNumbers=" + mobileNumbers +
            '}';
    }
}
 
class Address{
    private String zipcode;
 
    public Address(String zipcode) {
        this.zipcode = zipcode;
    }
 
    public String getZipcode() {
        return zipcode;
    }
 
    public void setZipcode(String zipcode) {
        this.zipcode = zipcode;
    }
}
 
class MobileNumber{
    private String number;
 
    public MobileNumber(String number) {
        this.number = number;
    }
 
    public String getNumber() {
        return number;
    }
 
    public void setNumber(String number) {
        this.number = number;
    }
}

 Scenario
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package com.javabypatel;
 
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;
 
public class StreamTest {
    public static void main(String[] args) {
 
        Student student1 = new Student(
            "Jayesh",
            20,
            new Address("1234"),
            Arrays.asList(new MobileNumber("1233"), new MobileNumber("1234")));
 
        Student student2 = new Student(
            "Khyati",
            20,
            new Address("1235"),
            Arrays.asList(new MobileNumber("1111"), new MobileNumber("3333"), new MobileNumber("1233")));
 
        Student student3 = new Student(
            "Jason",
            20,
            new Address("1236"),
            Arrays.asList(new MobileNumber("3333"), new MobileNumber("4444")));
 
        List<Student> students = Arrays.asList(student1, student2, student3);
 
        /*****************************************************
         Get student with exact match name "jayesh"
        *****************************************************/
        Optional<Student> stud = students.stream()
            .filter(student -> student.getName().equals("Jayesh"))
            .findFirst();
        System.out.println(stud.isPresent() ? stud.get().getName() : "No student found");
        System.out.println("--------------------");
 
        /*****************************************************
         Get student with matching address "1235"
        *****************************************************/
        Optional<Student> stud1 = students.stream()
            .filter(student -> student.getAddress().getZipcode().equals("1235"))
            .findFirst();
        System.out.println(stud1.isPresent() ? stud1.get().getName() : "No student found");
        System.out.println("--------------------");
 
        /*****************************************************
         Get all student having mobile numbers 3333.
        *****************************************************/
        List<Student> stud2 = students.stream()
            .filter(student111 -> student111.getMobileNumbers().stream().anyMatch(x -> Objects.equals(x.getNumber(), "3333")))
            .collect(Collectors.toList());
 
          String result1 = stud2.stream().map(std -> std.getName()).collect(Collectors.joining(",", "[", "]"));
          System.out.println(result1);
        System.out.println("--------------------");
 
        /*****************************************************
         Get all student having mobile number 1233 and 1234
         *****************************************************/
        List<Student> stud3 = students.stream()
            .filter(student -> student.getMobileNumbers().stream().allMatch(x -> Objects.equals(x.getNumber(), "1233") || Objects.equals(x.getNumber(), "1234")))
            .collect(Collectors.toList());
 
        String result4 = stud3.stream().map(std -> std.getName()).collect(Collectors.joining(",", "[", "]"));
        System.out.println(result4);
        System.out.println("--------------------");
 
        /*****************************************************
         Create a List<Student> from the List<TempStudent>
        *****************************************************/
        TempStudent tmpStud1 = new TempStudent(
            "Jayesh1",
            201,
            new Address("12341"),
            Arrays.asList(new MobileNumber("12331"), new MobileNumber("12341")));
 
        TempStudent tmpStud2 = new TempStudent(
            "Khyati1",
            202,
            new Address("12351"),
            Arrays.asList(new MobileNumber("11111"), new MobileNumber("33331"), new MobileNumber("12331")));
 
        List<TempStudent> tmpStudents = Arrays.asList(tmpStud1, tmpStud2);
 
        List<Student> studentList = tmpStudents.stream()
            .map(tmpStud -> new Student(tmpStud.name, tmpStud.age, tmpStud.address, tmpStud.mobileNumbers))
            .collect(Collectors.toList());
 
        System.out.println(studentList);
        System.out.println("--------------------");
 
        /*****************************************************
         Convert List<Student> to List<String> of student name
        *****************************************************/
        List<String> studentsName = studentList.stream()
            .map(Student::getName)
            .collect(Collectors.toList());
 
        System.out.println(studentsName.stream().collect(Collectors.joining(",")));
        System.out.println(studentsName.stream().collect(Collectors.joining(",", "[", "]")));
        System.out.println("--------------------");
 
        /*****************************************************
         Convert List<students> to String
        *****************************************************/
        String name = students.stream()
            .map(Student::getName)
            .collect(Collectors.joining(",", "[", "]"));
        System.out.println(name);
        System.out.println("--------------------");
 
        /*****************************************************
         Change the case of List<String>
        *****************************************************/
        List<String> nameList =
            Arrays.asList("Jayesh", "Dany", "Khyati", "Hello", "Mango");
 
        nameList.stream()
            .map(String::toUpperCase)
            .forEach(System.out::println);
        System.out.println("--------------------");
 
        /*****************************************************
         Sort List<String>
         *****************************************************/
        List<String> namesList =
            Arrays.asList("Jayesh", "Dany", "Khyati", "Hello", "Mango");
 
        namesList.stream()
            .sorted()
            .forEach(System.out::println);
        System.out.println("--------------------");
 
        /*****************************************************
         Conditionally apply Filter condition, say if flag is enabled then
         *****************************************************/
        boolean sortConditionFlag = true;
 
        Stream<Student> conditionalFilterResult = students.stream()
            .filter(std -> std.getName().startsWith("J"));
 
        if(sortConditionFlag){
            conditionalFilterResult = conditionalFilterResult.sorted(Comparator.comparing(Student::getName));
        }
 
        System.out.println("Before sorting :");
        students.forEach(s -> System.out.println(s.getName()));
 
        List<Student> list = conditionalFilterResult.collect(Collectors.toList());
        System.out.println("After filter and conditional sorting :");
        list.forEach(s -> System.out.println(s.getName()));
 
    }
}
Output
Jayesh
--------------------
Khyati
--------------------
[Khyati,Jason]
--------------------
[Jayesh]
--------------------
[Student{name='Jayesh1', age=201, address=com.javabypatel.sea.Address@685cb137, mobileNumbers=[com.javabypatel.sea.MobileNumber@6a41eaa2, com.javabypatel.sea.MobileNumber@7cd62f43]},

Student{name='Khyati1', age=202, address=com.javabypatel.sea.Address@6d4b1c02, mobileNumbers=[com.javabypatel.sea.MobileNumber@6093dd95, com.javabypatel.sea.MobileNumber@5622fdf, com.javabypatel.sea.MobileNumber@4883b407]}]
--------------------
Jayesh1,Khyati1
[Jayesh1,Khyati1]
--------------------
[Jayesh,Khyati,Jason]
--------------------
JAYESH
DANY
KHYATI
HELLO
MANGO
--------------------
Dany
Hello
Jayesh
Khyati
Mango
--------------------
Before sorting :
Jayesh
Khyati
Jason
After filter and conditional sorting :
Jason
Jayesh

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Enjoy !!!! 
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