Java 8 Stream Practice Problems

Java 8 Stream Practice Problems

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Java 8 Stream API is very useful for filtering collections. Lets see few java 8 stream practice questions.

Scenario

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By looking at below example class, answer the following questions, 

1. Get student with exact match name "jayesh"
2. Get student with matching address "1235"
3. Get all student having mobile numbers 3333.
4. Get all student having mobile number 1233 and 1234
5. Create a List<Student> from the List<TempStudent>
6. Convert List<Student> to List<String> of student name
7. Convert List<students> to String
8. Change the case of List<String>
9. Sort List<String>
10. Conditionally apply Filter condition, say if flag is enabled then.

package com.javabypatel; 

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;
    }
}

Solution

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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

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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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