Core Java Q&As Archives | Page 8 of 11 | 800+ Java & Big Data Interview Q&As

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Java 7 fork and join tutorial with a diagram and an example

Q. How does java.util.concurrent.RecursiveTask work? A. It uses a single ForkJoin pool to execute tasks in parallel for both computing sum of numbers recursively and chunking (or breaking) them into chunks of say 3 or less as per the following example. … Read more ›...

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Java 7: Top 8 new features with examples

There are several small new features and enhancements in Java 7. The major features and enhancements are in Java 8. Let’s look at the Java 7 new features. #1: string in switch statement:

public class Java7Feature1 {

 private static String color = "BLUE";

 private enum Color {
  RED, GREEN
 };

 public static void main(String[] args) {

  // Pre Java 5
  if (color.equals("RED")) {
   System.out.println("Color is Red");
  } else if (color.equals("GREEN")) {
   System.out.println("Color is Green");
  } else {
   System.out.println("Color not found");
  }

  // Java 5 enum. try/catch is required for colours other than RED and GREEN 
  try {
   switch (Color.valueOf(color)) {
   case RED:
    System.out.println("Color is Red");
    break;
   case GREEN:
    System.out.println("Color is Green");
   }
  } catch (IllegalArgumentException e) {
   System.out.println("Color not found");
  }

  // Java 7 String in switch statement for simplicity & better readability
  //JDK 7 switch performs better than if-else
  //using types with enums is only useful when it serves a meaningful purpose
  //the value for color could come from database, and string in switch is handy for this
  switch (color) {
  case "RED":
   System.out.println("Color is Red");
   break;
  case "GREEN":
   System.out.println("Color is Green");
   break;
  default:
   System.out.println("Color not found");
  }
 }

}

public class Java7Feature1 {

private static String color = "BLUE";

private enum Color {

RED, GREEN

};

public static void main(String[] args) {

// Pre Java 5

if (color.equals("RED")) {

System.out.println("Color is Red");

} else if (color.equals("GREEN")) {

System.out.println("Color is Green");

} else {

System.out.println("Color not found");

}

// Java 5 enum. try/catch is required for colours other than RED and GREEN

try {

switch (Color.valueOf(color)) {

case RED:

System.out.println("Color is Red");

break;

case GREEN:

System.out.println("Color is Green");

}

} catch (IllegalArgumentException e) {

System.out.println("Color not found");

}

// Java 7 String in switch statement for simplicity & better readability

//JDK 7 switch performs better than if-else

//using types with enums is only useful when it serves a meaningful purpose

//the value for color could come from database, and string in switch is handy for this

switch (color) {

case "RED":

System.out.println("Color is Red");

break;

case "GREEN":

System.out.println("Color is Green");

break;

default:

System.out.println("Color not found");

}

Output is:

Color not found
Color not found
Color not found

Color not found

#2 Binary integral literals

public class Java7Feature2 {

 public static void main(String[] args) {
  // Pre Java 7
  int n = Integer.parseInt("10000000", 2);
  System.out.println(n);

  n = 1 << 7;
  System.out.println(n);

  // Java 7
  n = 0b10000000; // 128 = 2^7
  System.out.println(n);
 }
}

public class Java7Feature2 {

public static void main(String[] args) {

// Pre Java 7

int n = Integer.parseInt("10000000", 2);

System.out.println(n);

n = 1 << 7;

System.out.println(n);

// Java 7

n = 0b10000000; // 128 = 2^7

System.out.println(n);

}

Output:

128
128
128

128

#3: Underscores for better readability in...

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Java 8 Functional Programming interview questions on currying

Currying (named after Haskell Curry) is the fact of evaluating function arguments one by one, producing a new function with one argument less on each step. Java 8 still does not have first class functions, but currying is “practically” possible with verbose type signatures, … Read more ›...

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Java 8 Functional Programming interview questions on Closures

Java 8 Functional Programming interview questions on Closures. Java 8’s support for closures is limited compared to other FP languages like JavaScript, Python, Scala, etc. Interviewers might be quizzing your understanding on this limitation. This extends Java 8 Functional Programming interview questions on currying. What is a Closure?… Read more...

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Java 8 String streams and finding the first non repeated character with functional programming

Q1.Find the first non repeated character in a given string input using Java 8 or later?
A1.Extends Find the first non repeated character in a given string input with Java 8 functional programming.

For example, an input string of “stress”

…

Java 8 using the Predicate functional interface

The java.util.function package in Java 8 has a number of functional interfaces. Let’s look at the Predicate interface that is used for filtering objects from a collection. Here is the Java 8 example: Step 1: Create a Driver domain class using the builder design pattern. … Read more ›...

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Java 8: 7 useful miscellaneous additions you must know

The much awaited addition in Java 8 are Lambda expressions to be used in functional programming and default and static methods in interfaces to support multiple behavior inheritance and helper methods. Here are a few other additional handy additions in Java 8. Addition #1: String.join( ) method, … Read more...

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Java 8: Different ways to sort a collection of objects in pre and post Java 8

The object we are going to sort is a Person.

public class Person  {
 
 public enum Gender {FEMALE, MALE};

 private String name;
 private Integer age;
 private Gender gender;

 public Person(String name, Integer age, Gender gender) {
  this.name = name;
  this.age = age;
  this.gender = gender;
 }

 //getter, setter, equals(...), and hashCode() methods skipped

 @Override
 public String toString() {
  return "Person [name=" + name + ", age=" + age + ", gender=" + gender + "]";
 }
}

public class Person {

public enum Gender {FEMALE, MALE};

private String name;

private Integer age;

private Gender gender;

public Person(String name, Integer age, Gender gender) {

this.name = name;

this.age = age;

this.gender = gender;

}

//getter, setter, equals(...), and hashCode() methods skipped

@Override

public String toString() {

return "Person [name=" + name + ", age=" + age + ", gender=" + gender + "]";

}

Option 1: Writing your own Comparator implementation. This can be done as an anonymous inner class instead of a separate class.

import java.util.Comparator;

public class PersonComparator implements Comparator<Person> {

 @Override
 public int compare(Person o1, Person o2) {
  
  //by gender first
  int i1 = o1.getGender().compareTo(o2.getGender());
  if (i1 != 0) return i1;
  
  //by name next
  int i2 =  o1.getName().compareTo(o2.getName());
  if (i2 != 0) return i2;
  
  //by age
  return o1.getAge().compareTo(o2.getAge());
 }
}

import java.util.Comparator;

public class PersonComparator implements Comparator<Person> {

@Override

public int compare(Person o1, Person o2) {

//by gender first

int i1 = o1.getGender().compareTo(o2.getGender());

if (i1 != 0) return i1;

//by name next

int i2 = o1.getName().compareTo(o2.getName());

if (i2 != 0) return i2;

//by age

return o1.getAge().compareTo(o2.getAge());

}

The test class

import java.util.ArrayList;
import java.util.List;

public class PersonTest {
 
 public static void main(String[] args) {
  
  List<Person> people = new ArrayList<>();
  people.add(new Person("John", 35, Person.Gender.MALE));
  people.add(new Person("John", 32, Person.Gender.MALE));
  people.add(new Person("Simone", 30, Person.Gender.FEMALE));
  people.add(new Person("Shawn", 30, Person.Gender.MALE));
  
  System.out.println("before sorting = "  + people);
  people.sort(new PersonComparator());
  System.out.println("after sorting = "  + people);
 
 }
}

import java.util.ArrayList;

import java.util.List;

public class PersonTest {

public static void main(String[] args) {

List<Person> people = new ArrayList<>();

people.add(new Person("John", 35, Person.Gender.MALE));

people.add(new Person("John", 32, Person.Gender.MALE));

people.add(new Person("Simone", 30, Person.Gender.FEMALE));

people.add(new Person("Shawn", 30, Person.Gender.MALE));

System.out.println("before sorting = " + people);

people.sort(new PersonComparator());

System.out.println("after sorting = " + people);

}

Option 2: The Option 1 is not bad, … Read more ›...

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Java 8: Does “Optional” class alleviate the pain of ubiquitous NullpointerException?

The most prevalent runtime exception (aka unchecked) exception in Java is the NullPointerException. You need to code defensively to avoid NullPointerException as shown below. Later, we will see how the class java.util.Optional that was introduced in Java 8 will alleviate this problem to some extent. … Read more ›...

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Java abstract classes Vs interfaces Interview Q&As

Q1. When to use an abstract class over an interface? Q2. What is a diamond problem? Q3. Does Java support multiple inheritance? In design, you want the base class to present only an interface (or a contract) for its derived classes. … Read more ›...

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Java classes and interfaces are the building blocks

Q1. Which class declaration is correct if A and B are classes and C and D are interfaces? a) class Z extends A implements C, D{} b) class Z extends A,B implements D {} c) class Z extends C implements A,B {} d) class Z extends C,D implements B {}...

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Java coding practice problems – prime and powerful

There is no other way to pass the Java coding tests other than practicing. I have failed Java coding tests due to lack of practice. How often do you get work with tree and graph data structures? Ho often do you work with algorithms?

50+ Java coding practice problems Links:

Can you write code in Java?

…

Java Compile-time Vs Run-time Interview Q&As

During development and design, one needs to think in terms of compile-time, run-time, and build-time. It will also help you understand the fundamentals better. These are beginner to intermediate level questions.

Q1.

…

Blog Archives

Java 7 fork and join tutorial with a diagram and an example

Java 7: Top 8 new features with examples

Java 8 Functional Programming interview questions on currying

Java 8 Functional Programming interview questions on Closures

Java 8 String streams and finding the first non repeated character with functional programming

Java 8 using the Predicate functional interface

Java 8: 7 useful miscellaneous additions you must know

Java 8: Different ways to sort a collection of objects in pre and post Java 8

Java 8: Does “Optional” class alleviate the pain of ubiquitous NullpointerException?

Java abstract classes Vs interfaces Interview Q&As

Java classes and interfaces are the building blocks

Java coding practice problems – prime and powerful

Java Compile-time Vs Run-time Interview Q&As

300+ Java Interview Questions - FAQs

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