Category Archives: Interview Questions

Prototype Pattern in Java

In this post, We will talk and learn about Prototype Pattern in Java. Prototype comes under a creational design pattern that makes use of cloning objects if object creation complex and time-consuming. Below is the complete source code: Student.java Model class

package com.kkjavatutorials.prototype;
/**
 * 
 * @author KK JavaTutorials
 *Model class
 */
public class Student {

	private Integer id;
	private String name;
	
	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
	
	@Override
	public String toString() {
		return "Student [Student id=" + id + ", Student name=" + name + "]";
	}
}

package com.kkjavatutorials.prototype;

/**

* @author KK JavaTutorials

*Model class

public class Student {

private Integer id;

private String name;

public Integer getId() {

return id;

}

public void setId(Integer id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

@Override

public String toString() {

return "Student [Student id=" + id + ", Student name=" + name + "]";

}

StudentDAO.java creates Cloned Object that makes use of Prototype Pattern:

package com.kkjavatutorials.prototype;

import java.util.ArrayList;
import java.util.List;
/**
 * @author KK JavaTutorials
 * Dummy Student DAO implementation
 * In Real Scenario Object can be constructed by calling database.
 */
public class StudentDAO implements Cloneable{

	private static List<Student> studentList;
	
	static {
		studentList = new ArrayList<>();

		Student student1 = new Student();
		student1.setId(10);
		student1.setName("PK");

		Student student2 = new Student();
		student2.setId(20);
		student2.setName("MK");

		studentList.add(student1);
		studentList.add(student2);
	}
	
	/**
	 * In Real Scenario Object can be constructed by calling database.
	 * @return Student List
	 */
	public List<Student> getAllStudents(){
		return studentList;
	}
	
	/**
	 * Creating Clone of an Existing object
	 */
	@Override
	public List<Student> clone() throws CloneNotSupportedException {
		
		List<Student> dummyStudentList = new ArrayList<>();
		for (Student student : studentList) {
			dummyStudentList.add(student);
		}
		return dummyStudentList;
	}
}

package com.kkjavatutorials.prototype;

import java.util.ArrayList;

import java.util.List;

/**

* @author KK JavaTutorials

* Dummy Student DAO implementation

* In Real Scenario Object can be constructed by calling database.

public class StudentDAO implements Cloneable{

private static List<Student> studentList;

static {

studentList = new ArrayList<>();

Student student1 = new Student();

student1.setId(10);

student1.setName("PK");

Student student2 = new Student();

student2.setId(20);

student2.setName("MK");

studentList.add(student1);

studentList.add(student2);

}

/**

* In Real Scenario Object can be constructed by calling database.

* @return Student List

public List<Student> getAllStudents(){

return studentList;

}

/**

* Creating Clone of an Existing object

@Override

public List<Student> clone() throws CloneNotSupportedException {

List<Student> dummyStudentList = new ArrayList<>();

for (Student student : studentList) {

dummyStudentList.add(student);

}

return dummyStudentList;

}

Test.java Client Program:

package com.kkjavatutorials.prototype.client;

import java.util.List;

import com.kkjavatutorials.prototype.Student;
import com.kkjavatutorials.prototype.StudentDAO;
/**
 * @author KK JavaTutorials
 *Client Program which uses cloned object
 */
public class Test {

	public static void main(String[] args) throws CloneNotSupportedException  {
		
		StudentDAO studentDAO = new StudentDAO();
		
		//Getting Original copy of student list
		List<Student> allStudents = studentDAO.getAllStudents();
		
		//Getting clone copy of student list
		List<Student> updatedStudentList = studentDAO.clone();
		Student student = new Student();
		student.setId(30);
		student.setName("SK");
		
		//Doing manipulation on cloned copy
		updatedStudentList.add(student);
		
		System.out.println("Original Student List::");
		allStudents.forEach(System.out::println);
		
		System.out.println("Updated Student List::");
		updatedStudentList.forEach(System.out::println);
	}
}

package com.kkjavatutorials.prototype.client;

import java.util.List;

import com.kkjavatutorials.prototype.Student;

import com.kkjavatutorials.prototype.StudentDAO;

/**

* @author KK JavaTutorials

*Client Program which uses cloned object

public class Test {

public static void main(String[] args) throws CloneNotSupportedException {

StudentDAO studentDAO = new StudentDAO();

//Getting Original copy of student list

List<Student> allStudents = studentDAO.getAllStudents();

//Getting clone copy of student list

List<Student> updatedStudentList = studentDAO.clone();

Student student = new Student();

student.setId(30);

student.setName("SK");

//Doing manipulation on cloned copy

updatedStudentList.add(student);

System.out.println("Original Student List::");

allStudents.forEach(System.out::println);

System.out.println("Updated Student List::");

updatedStudentList.forEach(System.out::println);

}

Output… Read More »

Singleton Design Pattern in java

In the previous post, Java Design Pattern which talks list of design patterns available in java In this post, we will learn what is Singleton design pattern and it’s different implementations. Singleton design patterns help us to create one and only one object of a class within the JVM. Singleton Eager initialization Singleton Lazy Initialization Thread Safe Singleton… Read More »

How to Convert List to Map using Java 8

In this post, we will learn How to convert List to Map using Java 8 Stream API, where a key is any attribute from the object and value is the object itself or any attribute from Object. Let’s clarify it using the below example. Employee.java

package com.kkjavatutorials.model;
 
public class Employee {
 
	private int id;
	private String name;
	private boolean isFemale;
	private boolean isMale;
	private Double salary;
	public Employee(int id, String name, boolean isFemale, boolean isMale, Double salary) {
		super();
		this.id = id;
		this.name = name;
		this.isFemale = isFemale;
		this.isMale = isMale;
		this.salary = salary;
	}
	public int getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	public boolean isFemale() {
		return isFemale;
	}
	public boolean isMale() {
		return isMale;
	}
	public Double getSalary() {
		return salary;
	}
	
	public void setSalary(Double salary) {
		this.salary = salary;
	}
	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", isFemale=" + isFemale + ", isMale=" + isMale + ", salary="
				+ salary + "]";
	}
}

package com.kkjavatutorials.model;

public class Employee {

private int id;

private String name;

private boolean isFemale;

private boolean isMale;

private Double salary;

public Employee(int id, String name, boolean isFemale, boolean isMale, Double salary) {

super();

this.id = id;

this.name = name;

this.isFemale = isFemale;

this.isMale = isMale;

this.salary = salary;

}

public int getId() {

return id;

}

public String getName() {

return name;

}

public boolean isFemale() {

return isFemale;

}

public boolean isMale() {

return isMale;

}

public Double getSalary() {

return salary;

}

public void setSalary(Double salary) {

this.salary = salary;

}

@Override

public String toString() {

return "Employee [id=" + id + ", name=" + name + ", isFemale=" + isFemale + ", isMale=" + isMale + ", salary="

+ salary + "]";

}

StreamApiExample.java

package com.kkjavatutorials.client;
 
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import com.kkjavatutorials.model.Employee;
/**
 * @author KK JavaTutorials
 *Convert List to Map using java 8 Stream API
 */
public class StreamApiExample {
	public static void main(String[] args) {
 
		Employee employee1 = new Employee(1002, "Sean", false, true, 10000.00);
		Employee employee2 = new Employee(1072, "Marry", true, false, 15000.00);
		Employee employee3 = new Employee(1882, "Sam", false, true, 30000.00);
		Employee employee4 = new Employee(1992, "Sofiya", true, false, 3000.00);
		Employee employee5 = new Employee(1112, "Raj", false, true, 16000.00);
		Employee employee6 = new Employee(1772, "Hema", true, false, 9000.00);
		
		//List of employees
		List<Employee> empList = new ArrayList<>();
		empList.add(employee1);
		empList.add(employee2);
		empList.add(employee3);
		empList.add(employee4);
		empList.add(employee5);
		empList.add(employee6);
		
		System.out.println("-------Getting Map from List where key = id, value = name in Map using Stream API----------");
		 // key = id, value = name
        Map<Integer, String> empIdAndNameMap = empList.stream().collect(
                Collectors.toMap(Employee::getId, Employee::getName));

        System.out.println("empIdAndNameMap : " + empIdAndNameMap);
        
        // Same as empIdAndNameMap but different syntax
        // key = id, value = name
        Map<Integer, String> empIdAndNameMap2 = empList.stream().collect(
                Collectors.toMap(e -> e.getId(), e -> e.getName()));

        System.out.println("empIdAndNameMap2 : " + empIdAndNameMap2);

        System.out.println("-------Getting Map from List where key = id, value = salary in Map using Stream API----------");
        // key = name, value = salary
        Map<String, Double> empNameAndSalaryMap = empList.stream().collect(
                Collectors.toMap(Employee::getName, Employee::getSalary));
        
        System.out.println("empNameAndSalaryMap : " + empNameAndSalaryMap);

        System.out.println("-------Getting Map from List where key = id, value = Employee Object in Map using Stream API----------");
        //key = id, value = Employee Object
        Map<Integer, Employee> collect = empList.stream().collect(Collectors.toMap(e->e.getId(),e->e));
        System.out.println(collect);
	}
}

package com.kkjavatutorials.client;

import java.util.ArrayList;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

import com.kkjavatutorials.model.Employee;

/**

* @author KK JavaTutorials

*Convert List to Map using java 8 Stream API

public class StreamApiExample {

public static void main(String[] args) {

Employee employee1 = new Employee(1002, "Sean", false, true, 10000.00);

Employee employee2 = new Employee(1072, "Marry", true, false, 15000.00);

Employee employee3 = new Employee(1882, "Sam", false, true, 30000.00);

Employee employee4 = new Employee(1992, "Sofiya", true, false, 3000.00);

Employee employee5 = new Employee(1112, "Raj", false, true, 16000.00);

Employee employee6 = new Employee(1772, "Hema", true, false, 9000.00);

//List of employees

List<Employee> empList = new ArrayList<>();

empList.add(employee1);

empList.add(employee2);

empList.add(employee3);

empList.add(employee4);

empList.add(employee5);

empList.add(employee6);

System.out.println("-------Getting Map from List where key = id, value = name in Map using Stream API----------");

// key = id, value = name

Map<Integer, String> empIdAndNameMap = empList.stream().collect(

Collectors.toMap(Employee::getId, Employee::getName));

System.out.println("empIdAndNameMap : " + empIdAndNameMap);

// Same as empIdAndNameMap but different syntax

// key = id, value = name

Map<Integer, String> empIdAndNameMap2 = empList.stream().collect(

Collectors.toMap(e -> e.getId(), e -> e.getName()));

System.out.println("empIdAndNameMap2 : " + empIdAndNameMap2);

System.out.println("-------Getting Map from List where key = id, value = salary in Map using Stream API----------");

// key = name, value = salary

Map<String, Double> empNameAndSalaryMap = empList.stream().collect(

Collectors.toMap(Employee::getName, Employee::getSalary));

System.out.println("empNameAndSalaryMap : " + empNameAndSalaryMap);

System.out.println("-------Getting Map from List where key = id, value = Employee Object in Map using Stream API----------");

//key = id, value = Employee Object

Map<Integer, Employee> collect = empList.stream().collect(Collectors.toMap(e->e.getId(),e->e));

System.out.println(collect);

}

Output of this program: ——-Getting Map from… Read More »

Java Program for Armstrong number ?

In the previous post, How to check Armstrong number java program we learned what is Armstrong number and How to write a Java program to test whether the given input number is Arm Strong or not. In this post, I will show you a different approach to write the java program for Arm Strong number. Below is… Read More »

Semaphore Example in Java ?

In this post, We will talk and learn about Semaphore in Java using an Example. A counting Semaphore is from java.util.concurrent package which maintains a set of permits. Each call of acquire() blocks if necessary until a permit is available, and then takes it. Each call of release() adds a permit. The Semaphore usually keeps a count of the number available… Read More »

CyclicBarrier Example in Java ?

In this post, We will talk and learn about CyclicBarrier in Java using an Example. A CyclicBarrier is a synchronization helping class from java.util.concurrent package that allows a set of threads to all wait for each other to reach at common barrier point. CyclicBarrier is useful when a program involves a fixed sized party of threads… Read More »

CountDownLatch Example in Java

In this post, We will talk and learn about CountDownLatch in Java using an Example. CountDownLatch is a synchronization helping class that allows one or more threads to wait until a set of operations being performed in other threads completes. A CountDownLatch has to initialize with a given count. The await method blocks until and unless the current count reaches to… Read More »

Java Spliterator Example

In this post, We will talk and learn about Java Spliterator Using an example Java Spliterator interface is an example of an internal iterator that breaks down the stream into the smaller parts and these smaller parts can be processed in parallel. Features Of Spliterator : The following are the list of features provided by Spliterator in Java. Spliterator… Read More »

Differences Between map() And flatMap() in Java 8 ?

In this post, we will clarify Differences Between map() And flatMap() in Java 8 using an example Below both Methods are available in java.util.stream.Stream Interface from Java 8 onwards <R> Stream<R> map(Function<? super T, ? extends R> mapper); <R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper); These two methods map and flatMap can be… Read More »

How to find intersection of two LinkedList in java ?

In this post, we will talk and learn How to find Intersection of two linked lists. Let’s say there are two singly LinkedList’s because of some programming error, the end node of one of the LinkedList got linked to the second LinkedList and formed a Y shaped list. We have to write a program to get… Read More »