Top 10 Books essential for Java Programmers

Top 10 Books essential for Java Programmers

Top 10 Books essential books for Java Programmers. Effective Java. There should not be any surprise here. Clean Code. Another timeless classic for Java programmers is Clean Code. Java Concurrency in Practice. Head First Design Patterns. Spring in Action. Test Driven...

Today, I am going to share the 10 best Java books that every Java developer should read. Even if some knowledge is out-dated, most of the stuff you learn will help build upon your knowledge and a life-time career..

Top 10 Books essential books for Java Programmers

Without further ado, here is my list of some of the most popular and important books for Java programmers. If you have been a Java programmer for 2 to 3 years, it's a good chance that you have read these book already. But, if you haven't, now is the best time to read them. You will not regret investing your time and money on these books, because the payback is limitless.

1. Effective Java

There should not be any surprise here. Effective Java by Joshua Bloch is hands down best Java book ever. This is a definite must-read book for Java programmers of any experience level. You will learn so much about Java and its API then you could imagine.

The fact that Joshua Bloch himself is the author of several key Java classes and API, e.g. java.lang and Java Collection framework, is enough reason to read this book. Along with that, his writing style is also fantastic.

You can read this book on a beach, while traveling, or just at your desk. It's awesome. There is no doubt that you would emerge as better Java programmer after reading this book.

And the best thing is that a new edition of Effective Java is available now, which covers Java 7, 8, and 9. There cannot be a better time to read this book.

2. Clean Code

Another timeless classic for Java programmers is Clean Code. As the title suggests, it teaches you to write better code, which is such a difficult thing to learn. To be honest, it's easy to learn Java, but difficult to write better Java code which uses strong OOP principles and that's where this book helps.

Similar to Joshua Bloch, Robert C. Martin, also known as Uncle Bob, is an excellent author and shares a lot of his experience as a software developer, teaching you various programming techniques and practices that help a lot in your day-to-day job as a programmer.

3. Java Concurrency in Practice

Multithreading and concurrency is an essential part of Java programming. There is no better book than Brian Goetz's Java Concurrency in Practice to learn and master this tricky topic.

Even though the book only covers Java 5, it's still relevant and a must-read books for any serious Java developer.

Some of you may find that some of the sections are a bit difficult to understand, especially sections 3.5.1 through 3.5.6, And if that's the case, I suggest you go through the Extreme Java - Concurrency Performance course by Dr. Heinz Kabutz. This will help you to better digest and comprehend those topics.

4. Head First Design Patterns

A good knowledge of OOP and design patterns are important for writing any Java application. Head First Design Patterns is the best book for learning to do that.

As I have said before, this was one of the first books I ever read on Java, apart from textbooks. After reading this book, I was very impressed. This is the book that taught me why Composition is better than Inheritance and how you can change runtime behavior of a class without touching the already tried and tested code.

You might think that it's just another old book, but you don't need to worry, an updated copy that covers Java SE 8 was released a couple of years ago.

If you are serious about learning design patterns in Java, this is the book you should read!

5. Spring in Action

Sorry, but I have to include one Spring book, Spring in Action, in this list of classic books for Java programmers. Spring is the most popular Java framework ever and this is the best book to learn about the Spring framework, but — to be honest — this book is much more than a Spring book.

After reading the 4th Edition of this book, I realized so much about Java and writing better code that I can't begin to explain.

The books take a topic, e.g. JDBC, and explain where JDK went wrong and how Spring corrects that mistake, e.g. SQLException, a one-size-fits-all exception that says something is wrong but not exactly what is wrong or how to deal with that.

Like Josuha Bloch and Uncle Bob, Craig Walls is another great author and you will learn much more than just Spring by reading this book.

6. Test Driven

Automation testing is an important skill. For developers, it all starts with unit testing. Java has been blessed to have the JUnit from the start, but just knowing the library doesn't make you a professional programmer who can write tests.

It takes much more than knowing a unit testing library, like JUnit or Mockito, and that's where this book helps. If you are serious about code quality and writing unit, integration, and automation test, Test Drivenis the book to read in 2018.

7. The Definitive Guide to Java Performance

Another aspect of becoming a better Java developer is knowing about JVM, Garbage collection, and performance tuning. Though there have been several good books on this topic, e.g. Java Performance by Binu John and Charlie Hunt, The Definitive Guide of Java Performance by Scott Oaks is my favorite.

Even though it only covers until JDK 7, you will learn a lot about performance tuning and JVM in general, which totally justifies the time and money you will spend on this book.

8. Head First Java

How many of you started learning Java by reading this book? Well, I did. Just after I came to know about Head First Design Pattern, I also found this book, Head First Java, and I really enjoyed reading it. I learned a lot of Java concepts and many of my misconceptions were also corrected.

Though many feel this is an out-of-date book, I still feel its a great book for anyone just starting with Java because of its unique style and content.

You can easily learn about Java 8, Java 9, and Java 10 changes on other versions once you know Java by reading this book.

9. Head First Object-Oriented Analysis and Design

Here is another "Head First" book in the list of the greatest Java books. Yup, they are simply awesome.

Head First Object-Oriented Analysis and Design forms a trilogy of the "Head First" books for Java programmers, i.e. Head First Java, Head First Design Patterns, and Head First OOAD.

It actually complements Head First Design Patterns by explaining the techniques of object-oriented programming and design.

The most important technique that I learned from this book was coding for interfaces and how to encapsulate what changes. This book simply changed how I write Java code.

10. Java: A Beginner's Guide

If you ever need a comprehensive Java book, this should be it. Even though the title says Java: A Beginner's Guide, it's one of the most complete books for learning Java.

Sir Herbert Schildt has also done a commendable job in keeping the book up-to-date, e.g. the 7th Edition of this book now covers Java 9.

Though, I don't know how he is going to keep this book up-to-date going forward, since Java's new 6-month release cycle which started with Java 10.

These are some of the best books for Java programmers. If you are a passionate Java programmer, there is a good chance that you have already read most of these books. But, if you haven't, then 2019 may be just the right time to read these books.

It's great that you appreciate this, thanks for reading !

Java to C# – C# to Java

Java to C# – C# to Java

In this post, we bring you a much needed Rosetta Stone — an explanatory bridge between these two technologies

Originally published by Andy Macdonald at https://medium.com
Java and C# are incredibly similar. Both languages are somewhat derived from C++ and from similar first principles.

Java was developed in 1995 to create a language with a simpler programming model than C++ while still preserving some of the same syntax of the language to facilitate developers transitioning to it.

C# was developed in 2000 by Microsoft as part of its .NET drive in order to develop a language and set of technologies that could address some of the perceived weaknesses of the C++ language. It was also developed with quite heavy “inspiration” from the Java language.

Despite the similarities between the languages and sharing some common ground, transitioning from one technology to the other for a developer well-practised in one technology can be quite tricky.

Innovation happens best when there is collaboration between people of different mindsets — yet users of C# and Java can be somewhat tribalistic.

To that end, I thought it would be useful to put together a sort of guide to help people thinking about or starting to transition between these two technologies. It would also be nice in some way to facilitate a bit more collaboration between these two worlds — hopefully to do my bit to reduce the needless gulf that exists between them.

Some of the similarities right off the bat:

Java is a language that runs in a virtual machine environment (JVM) and runs bytecode that the Java compiler generates.

For C#, the situation is similar. It is a language that runs on the .NET framework and the CLR runtime. It uses a similar intermediary language to Java bytecode called MSIL which gets run via CLR.

Naming and Conventions

Some of the key and most immediately obvious differences in nomenclature, syntax, and conventions are:

  • “Projects” (Java) — “Solutions” (C#)
  • In Java, methods use lowerCamelCase (bar.doAThing()), whilst in C# public methods use PascalCase (bar.DoAThing())
  • In C#, interfaces are always prefixed with an I, as in IUserService<T>, instead of UserService<T>** **in Java
  • In Java, a string is a String** **— in C# a string is a string
  • “POJO” (Java) — “POCO” (C#)
  • Packages (Java) — Namespaces (C#)

Package (Java)

package dev.andymacdonald;

// Code goes here

Namespace (C#)

namespace Dev.AndyMacdonald 
{
  // Code goes here
}

Syntax

**Java has <strong>final</strong> variables — C# has **<strong>readonly</strong>

A key difference here is that Java final variables can be assigned once anywhere in the class, whereas C#’s readonly variables can only be assigned in the constructor.

C# has <strong>out</strong> and <strong>ref</strong> parameters to allow passing arguments by reference — Java doesn’t

It can manipulate objects and variables by reference, but in a method, these arguments are passed by a value. With C#, we can override this behaviour with the out and ref keywords.

Annotations (Java) — attributes (C#)

These are basically equivalent concepts and just differ in actual syntax. Both annotations and attributes can be accessed via each language’s respective Reflection API implementation.

Java annotation:

@PersonallyIdentifiable
private String fullName;

C# attribute:

[PersonallyIdentifiable]
private string fullName;

Getters and setters or Project Lombok (Java) — C# properties

C# really overtakes Java here with its built-in properties* *feature. In the standard JDK, there isn’t an equivalent to this, and instead, in Java, getters and setters must be written for each field requiring an accessor.

These are often just generated by the developer with their IDE as a cheat … still a bit tedious, though.

Java getters and setters:


public class Element 
{
   
  private String symbol;   
  private String name;   
  private int atomicNumber;
  public int getAtomicNumber() 
  {
    return this.atomicNumber;
  }
  public String getSymbol() 
  {
    return this.symbol;
  }
  public String getName() 
  {
    return this.name; 
  }
  public void setAtomicNumber(int atomicNumber) 
  {
    this.atomicNumber = atomicNumber;
  }
  public void setName(String name) 
  {
    this.name = name;
  }
  public void setSymbol(String symbol) 
  {
    this.symbol = symbol;
  }
}

Many Java projects incorporate Project Lombok, which adds getters, setters, equals, and hash code (plus other useful boilerplates) at compile time.

Project Lombok — not part of the standard library:

@Getter @Setter
public class Element 
{
   
  private String symbol;   
  private String name;   
  private int atomicNumber;
}

C# built-in properties feature:

public class Element 
{

  public string Symbol { get; set; }     
  public string Name { get; set; }     
  public int AtomicNumber { get; set; }
}

Loops

Java for each loop:

List<Integer> fibNumbers = Arrays.asList(0, 1, 1, 2, 3, 5, 8, 13);
int count = 0;
for (int element: fibNumbers)
{
    count++;
    System.out.println(String.format("Element #%s: %s", count, element));
}
System.out.println(String.format("Number of elements: %s", count));

C# for each loop:

var fibNumbers = new List<int> { 0, 1, 1, 2, 3, 5, 8, 13 };
int count = 0;
foreach (int element in fibNumbers)
{
    count++;
    Console.WriteLine($"Element #{count}: {element}");
}
Console.WriteLine($"Number of elements: {count}");

Implementing interfaces/inheritance

Inheritance and implementing interfaces isn’t drastically different between the two languages. Java uses the extends or implements keywords; C# uses C++ syntax (derivation declaration) B : A for defining inheritance.

Defining and implementing an interface with methods in Java:

package dev.andymacdonald;


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

interface Fish
{
   void swim();
}

class Salmon implements Fish
{

   public void swim()
   {
      System.out.println("Salmon.Fish");
   }
}

class Cod implements Fish
{
   public void swim()
   {
      System.out.println("Cod.Swim");
   }
}

public class Program
{
   public static void main()
   {
      List<Fish> fishes = new ArrayList<>();
      fishes.add(new Salmon());
      fishes.add(new Cod());

      for (Fish fish : fishes)
      {
         fish.swim();
      }
   }
}

Defining and implementing an interface with methods in C#:

using System;
using System.Collections.Generic;

namespace Dev.AndyMacdonald 
{
    interface Fish
    {
        void Swim();
    }
    class Salmon : Fish
    {
        public void Swim()
        {
            Console.WriteLine("Salmon.Fish");
        }
    }
    class Cod : Fish
    {
        public void Swim()
        {
            Console.WriteLine("Cod.Swim");
        }
    }
    class Program
    {
        static void Main()
        {
            List<Fish> fishes = new List<Fish>();
            fishes.Add(new Salmon());
            fishes.Add(new Cod());
            foreach (Fish fish in fishes)
            {
                fish.Swim();
            }
        }
    }
}

Pointers

Quite simply, Java just doesn’t do pointers, whereas in C# it is possible to do pointer arithmetic and manipulation.

 unsafe {
  int a = 25;
  int * ptr = &a;
  Console.WriteLine($"Value of pointer is {*ptr}");
}

IDE

Visual Studio

C# developers traditionally and typically use the Visual Studio IDE. This is a situation borne out of the origins of .NET being a closed-source technology. Microsoft developed Visual Studio** **to be a one-stop shop for all things .NET.

Java went down a different route, offering much more developer choice in tooling from the outset. That’s why there’s a much greater range of IDEs for Java development (e.g., IntelliJ, Eclipse, NetBeans). Gradually the landscape for .NET developers has shifted, and more IDEs and developer choice has been offered over the years.

IntelliJ (Java) — Rider (C#)

Users of JetBrains IDEs will find the transition from one IDE to another very smooth if they choose to make a switch to the respective JetBrains IDE in the technology they are targeting. Keyboard shortcuts, IDE layout, and even some plugins are equivalent or comparable — virtually the same IDE.

Dependency Management

Maven (Java) — NuGet and dotnet CLI (C#)

Maven is a tool responsible for dependency management and the life cycle of the building of typically Java and JVM applications. That said, it is pretty flexible, has 1000s of plugins, and can be used to build applications of other languages, such as PHP and JavaScript.

The configurable unit of maven is a pom.xml file that every maven project has. For a project’s submodules, it is possible to have a pom file per submodule which inherits from a parent. Maven uses a remote server or repository of some kind to host and retrieve packages.

Maven pom.xml file (Java):

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>dev.andymacdonald</groupId>
    <artifactId>fish-app</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

At the simplest level, you can test and build a Maven project with the following command:

mvn clean install

And create a package with this:

mvn clean package

And finally, deploy a package like this:

mvn clean deploy

NuGet fulfills a similar, though not identical role in .NET to Maven. NuGet can use a few different configuration files but commonly uses .csproj*. *As with Maven, NuGet uses a server/repository that can host packages.

NuGet .csproj file:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <AssemblyName>MSBuildSample</AssemblyName>
    <OutputPath>Bin\</OutputPath>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="helloworld.cs" />
  </ItemGroup>
  <ItemGroup>
    <PackageReference Include="MyDependency" version="1.0.0" />
  </ItemGroup>  
  <Target Name="Build">
    <MakeDir Directories="$(OutputPath)" Condition="!Exists('$(OutputPath)')" />
    <Csc Sources="@(Compile)" OutputAssembly="$(OutputPath)$(AssemblyName).exe" />
  </Target>
</Project>

NuGet’s primary role is package management, construction, and deployment. Java developers will notice that it doesn’t really have the same concept of build phases as Maven does. Additionally, .NET developers don’t tend to edit their build files manually as Java developers do with pom.xml files, preferring to manipulate them in their IDE instead.

Packages can be built, packaged, and deployed to NuGet with the following nuget commands:

nuget spec
nuget pack {nuspec file}
nuget push {package file} {apikey} -Source {host url}

If you want to run the tests for your .NET application, you can run the following dotnet CLI command:

dotnet test

The dotnet CLI can also be used as a wrapper around nuget commands.

Application Servers

Apache Tomcat (Java) — IIS (ASP.NET)

Tomcat is an open-source web server and servlet container from the Apache Foundation. Though there are many other application servers used widely in Java, it is a pretty common choice for most enterprise-software companies. It works across pretty much every operating system (e.g., Windows, Unix, Linux, and Mac OS).

.NET projects are typically deployed on IIS, a web server that only runs on Windows. While its portability is limited, it’s a pretty popular choice for Windows developers because of its ease of use and simplicity while still offering some advanced configuration options.

… But Wait!

For .NET Core web applications, you can package them to run as standalone web applications — allowing you to run them like this:

dotnet <app_assembly>.dll

In the same way you can run a Java Spring Boot web*** ***application (which has a self-contained Tomcat server):

java -jar <my-application>.jar

And visit your shiny new web app like this:

http://<serveraddress>:<port>

Libraries and Frameworks

Spring Framework (Java) — ASP.NET (C#)

The Spring Framework is a framework and IoC container for Java. In short, the Spring framework is responsible for instantiating objects (beans) and managing the life cycle of these beans in memory.

Create an ApplicationContext* *(similar to the concept of a Startup in ASP.NET). This example uses Spring Boot:

@SpringBootApplication
public class HumanApplication
{
   public static void main(String[] args) 
   {
      SpringApplication.run(HumanApplication.class, args);
   }
}

Create an interface:

public interface Organ<T>
{  
   void function();
}

Implement the Organ<T> interface:

@Component
public class Heart implements Organ<Heart>
{
    public Heart() {}
    public void function() 
    {
        System.out.println("Buh-dump");
    }
}

Constructor injection of Organ dependencies list into a Human service:

@Service
public class Human 
{
    private static final int MAX_SECONDS_OF_LIFE = 3000;
    private List<Organ> organs;
    public Human(List<Organ> organs) 
    {
        this.organs = organs;
    }
    @PostConstruct
    public void live() 
    {
        for (int i = 0; i < MAX_SECONDS_OF_LIFE; i++) 
        {
            organs.forEach(organ -> organ.function());
        }
    }
}

Run the application …

It’s aliiiiiiive:

Buh-dump
Buh-dump
Buh-dump
Buh-dump
...

Spring also ships with a handy suite of modules and packages.

In the core Spring packages, and in the convention-over-configuration extension to the framework, Spring Boot, useful combinations of existing and bespoke technologies are provided for developers wanting access to common libraries to kickstart a project with all that they may need, rather than having to write or track down these utilities themselves:

  • RestTemplate (spring-web — for constructing REST and HTTP requests)
  • JdbcTemplate (spring-data — for constructing JDBC queries and statements)
  • Spring Security (for creating and managing application security models)
  • ObjectMapper (spring-core — useful utility for mapping POJOs from Jackson)
  • etc.

ASP.NET fulfills a similar role in the world of C#, providing IoC functionality, commonly used technologies, and utilities in a single framework. However, ASP.NET generally only provides IoC functionality for web applications, whereas the Spring Framework provides this for any application type.

In terms of dependency inversion, it is possible to do very similar things in ASP.NET as in Spring.

As before, define the needed interface and concrete implementation:

public interface Organ<T>
{  
   void Function();
}
public class Heart : Organ<Heart>
{
    public Heart() {}
    public void Function() 
    {
        Console.WriteLine("Buh-dump");
    }
}

Invoke functions of injected dependencies:

public class Human
{

   private List<IOrgan> _organs;
 
   public Human(List<IOrgan> organs)
   {
      _organs = organs;
      this.Live();
   }
   public void Live()
   {
      organs.ForEach(organ =>
      {
         organ.Function();
      });
   }
}

Define a Startup and register services:

public class Startup  
{    
  public void ConfigureServices(IServiceCollection services)
  {    
    services.AddTransient<IList<IOrgan>>(p => p.GetServices<IOrgan>().ToList());
  }
}

ASP.NET also fulfills the role of providing many useful libraries and utilities to accelerate development of your project.

Streams (Java) — LINQ (C#)

Both Java and C# have mechanisms to simplify the reduction of data sets — Streams and LINQ.

There are some differences and gaps between the two technologies but if you have familiarity with one, you’ll be able to get up and running fairly quickly with the other.

Java Streams:

List<Student> studentList = Arrays.asList( 
    new Student(1, "John", 18, 1),
    new Student(2, "Steve", 21, 1),
);
List<String> studentNames = studentList.stream()
    .filter(s -> s.getAge() > 18)
    .filter(s -> s.getStandardID() > 0)
    .map(s -> s.getName()).collect(Collectors.toList());
studentNames.forEach(name -> System.out.println(name));

LINQ Query (C#):

IList<Student> studentList = new List<Student>() { 
    new Student() { StudentID = 1, StudentName = "John", Age = 18, StandardID = 1 } ,
    new Student() { StudentID = 2, StudentName = "Steve",  Age = 21, StandardID = 1 }
};
var studentNames = studentList.Where(s => s.Age > 18)
                        .Where(st => st.StandardID > 0)
                        .Select(s => s.StudentName);
foreach(var name in studentNames) {   
    Console.WriteLine(name);
}

Apache Commons (Java) — CommonLibrary.NET (C#)

Apache Commons*** ***provides Java developers with a collection of several independently released, useful components and utilities for the purposes of accelerating development.

If you’re in need of a utility to work with ZIP files or a set of utilities for working with mathematical expressions and formulae, then Apache Commons has you covered.

In a similar way, CommonLibrary.NET covers these bases too — there are some key differences in naming of some components and modules, but for the most part, they are pretty much equivalent in their purpose.

That said, unlike Apache Commons, CommonLibrary.NET is quite old and isn’t very commonly used in projects anymore. If you’re after a continuously updated, curated list of libraries for each respective technology, I highly recommend these two lists:

akullpp/awesome-java

quozd/awesome-dotnet

Testing Libraries

JUnit (Java) — NUnit (C#)

Java’s ever-dependable JUnit library has a direct equivalent in C#.

NUnit has almost equivalent functionality to JUnit and is a popular choice for C# developers.

JUnit:

@Test
public void complexNumberTest()
{
    ComplexNumber result = someCalculation();
    Assert.assertEquals("Real", 5.2, result.getRealPart());
    Assert.assertEquals("Imaginary" 3.9, result.getImaginaryPart());
}

NUnit:

[Test]
public void ComplexNumberTest()
{
    ComplexNumber result = SomeCalculation();
    Assert.Multiple(() =>
    {
        Assert.AreEqual(5.2, result.RealPart, "Real");
        Assert.AreEqual(3.9, result.ImaginaryPart, "Imaginary");
    });
}

(Rumour has it NUnit started life as the JUnit source code modified to run in C#.)

Mockito (Java) — Moq (C#)

As with JUnit and NUnit, comparable functionality exists between Java’s Mockito and C#’s Moq library.

Mockito:

Foo mockFoo = mock(Foo.class);
when(mockFoo.doSomething("ping")).thenReturn(true);

Moq:

var mock = new Mock<IFoo>();
mock.Setup(foo => foo.DoSomething("ping")).Returns(true);

That’s It

Thanks for Reading!

I obviously couldn’t fit every difference, similarity, and detail in this article —* *it’s already far too long.

I hope at least I’ve covered enough ground to make you feel confident to make a switch and see how the other half lives.

If you liked this post, share it with all of your programming buddies!

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Further reading

Java Tutorial for Absolute Beginners

100+ Java Interview Questions and Answers In 2019

Python vs Java: Understand Object Oriented Programming

Angular 7 + Spring Boot CRUD Example

Build a Simple CRUD App with Spring Boot and Vue.js

Java String – String Functions In Java With Examples

Java String – String Functions In Java With Examples

In this post, we will be discussing about a new concept, Java String. String is a sequence of characters. But in Java, a string is an object that represents a sequence of characters. The java.lang.String class is used to create string object.

Originally published by Aayushi Johari at https://www.edureka.co
There are two ways to create a String object:
By string literal : Java String literal is created by using double quotes. For Example: String s=“Welcome”; By new keyword : Java String is created by using a keyword “new”. For example: String s=new String(“Welcome”); It creates two objects (in String pool and in heap) and one reference variable where the variable ‘s’ will refer to the object in the heap.
Now, let us understand the concept of Java String pool.

**Java String Pool: **Java String pool refers to collection of Strings which are stored in heap memory. In this, whenever a new object is created, String pool first checks whether the object is already present in the pool or not. If it is present, then same reference is returned to the variable else new object will be created in the String pool and the respective reference will be returned. Refer to the diagrammatic representation for better understanding:

In the above image, two Strings are created using literal i.e “Apple” and “Mango”. Now, when third String is created with the value “Apple”, instead of creating a new object, the already present object reference is returned. That’s the reason Java String pool came into the picture.

Before we go ahead, One key point I would like to add that unlike other data types in Java, Strings are immutable. By immutable, we mean that Strings are constant, their values cannot be changed after they are created. Because String objects are immutable, they can be shared. For example:

   String str =”abc”;

is equivalent to:

char data[] = {‘a’, ‘b’, ‘c’};
     String str = new String(data);

Let us now look at some of the inbuilt methods in String class.

Java String Methods

Java String length(): The Java String length() method tells the length of the string. It returns count of total number of characters present in the String. For example:

public class Example{
public static void main(String args[]{
String s1="hello";
String s2="whatsup";
System.out.println("string length is: "+s1.length()); 
System.out.println("string length is: "+s2.length());
}}

Here, String length() function will return the length 5 for s1 and 7 for s2 respectively.
Java String compareTo(): The Java String compareTo() method compares the given string with current string. It is a method of* ‘Comparable’* interface which is implemented by String class. Don’t worry, we will be learning about String interfaces later. It either returns positive number, negative number or 0. For example:

public class CompareToExample{
public static void main(String args[]){
String s1="hello";
String s2="hello";
String s3="hemlo";
String s4="flag";
System.out.println(s1.compareTo(s2)); // 0 because both are equal
System.out.println(s1.compareTo(s3)); //-1 because "l" is only one time lower than "m"
System.out.println(s1.compareTo(s4)); // 2 because "h" is 2 times greater than "f"
}} 

This program shows the comparison between the various string. It is noticed that

if s1 > s2, it returns a positive number

if s1 < s2, it returns a negative number

if s1 == s2, it returns 0
**Java String concat() : **The Java String concat() method combines a specific string at the end of another string and ultimately returns a combined string. It is like appending another string. For example:

public class ConcatExample{
public static void main(String args[]){
String s1="hello";
s1=s1.concat("how are you");
System.out.println(s1);
}}

The above code returns “hellohow are you”.
Java String IsEmpty() : This method checks whether the String contains anything or not. If the java String is Empty, it returns true else false. For example:

public class IsEmptyExample{
public static void main(String args[]){
String s1="";
String s2="hello";
System.out.println(s1.isEmpty());      // true
System.out.println(s2.isEmpty());      // false
}}

  • Java String Trim() : The java string trim() method removes the leading and trailing spaces. It checks the unicode value of space character (‘u0020’) before and after the string. If it exists, then removes the spaces and return the omitted string. For example:
public class StringTrimExample{ 
public static void main(String args[]){ 
String s1="  hello   "; 
System.out.println(s1+"how are you");        // without trim() 
System.out.println(s1.trim()+"how are you"); // with trim() 
}}  

In the above code, the first print statement will print “hello how are you” while the second statement will print “hellohow are you” using the trim() function.

  • Java String toLowerCase() : The java string toLowerCase() method converts all the characters of the String to lower case. For example:
public class StringLowerExample{
public static void main(String args[]){
String s1="HELLO HOW Are You?”;
String s1lower=s1.toLowerCase();
System.out.println(s1lower);}
}

The above code will return “hello how are you”.

  • Java String toUpper() : The Java String toUpperCase() method converts all the characters of the String to upper case. For example:
public class StringUpperExample{ 
public static void main(String args[]){ 
String s1="hello how are you"; 
String s1upper=s1.toUpperCase(); 
System.out.println(s1upper); 
}}

The above code will return “HELLO HOW ARE YOU”.
Java String ValueOf(): This method converts different types of values into string.Using this method, you can convert int to string, long to string, Boolean to string, character to string, float to string, double to string, object to string and char array to string. The signature or syntax of string valueOf() method is given below: public static String valueOf(boolean b) public static String valueOf(char c) public static String valueOf(char[] c) public static String valueOf(int i) public static String valueOf(long l) public static String valueOf(float f) public static String valueOf(double d) public static String valueOf(Object o)
Let’s understand this with a programmatic example:

public class StringValueOfExample{
public static void main(String args[]){
int value=20;
String s1=String.valueOf(value);
System.out.println(s1+17);       //concatenating string with 10
}}

In the above code, it concatenates the Java String and gives the output – 2017.
Java String replace(): The Java String replace() method returns a string, replacing all the old characters or CharSequence to new characters. There are 2 ways to replace methods in a Java String.

public class ReplaceExample1{
public static void main(String args[]){
String s1="hello how are you";
String replaceString=s1.replace('h','t');
System.out.println(replaceString); }}

In the above code, it will replace all the occurrences of ‘h’ to ‘t’. Output to the above code will be “tello tow are you”. Let’s see the another type of using replace method in java string:

**Java String replace(CharSequence target, CharSequence replacement) method **:

public class ReplaceExample2{
public static void main(String args[]){
String s1="Hey, welcome to Edureka";
String replaceString=s1.replace("Edureka","Brainforce");
System.out.println(replaceString);
}}

In the above code, it will replace all occurrences of “Edureka” to “Brainforce”. Therefore, the output would be “ Hey, welcome to Brainforce”.
Java String contains() :The java string contains() method searches the sequence of characters in the string. If the sequences of characters are found, then it returns true otherwise returns false. For example:

class ContainsExample{
public static void main(String args[]){
String name=" hello how are you doing";
System.out.println(name.contains("how are you"));  // returns true
System.out.println(name.contains("hello"));        // returns true 
System.out.println(name.contains("fine"));         // returns false 
}}

In the above code, the first two statements will return true as it matches the String whereas the second print statement will return false because the characters are not present in the string.
Java String equals() : The Java String equals() method compares the two given strings on the basis of content of the string i.e Java String representation. If all the characters are matched, it returns true else it will return false. For example:

public class EqualsExample{
public static void main(String args[]){
String s1="hello";
String s2="hello";
String s3="hi";
System.out.println(s1.equalsIgnoreCase(s2));   // returns true
System.out.println(s1.equalsIgnoreCase(s3));   // returns false
}
}

  • **JavaString equalsIgnoreCase(): **This method compares two string on the basis of content but it does not check the case like equals() method. In this method, if the characters match, it returns true else false. For example:
public class EqualsIgnoreCaseExample{
public static void main(String args[]){
String s1="hello";
String s2="HELLO";
String s3="hi";
System.out.println(s1.equalsIgnoreCase(s2));   // returns true
System.out.println(s1.equalsIgnoreCase(s3));   // returns false
}}

In the above code, the first statement will return true because the content is same irrespective of the case. Then, in the second print statement will return false as the content doesn’t match in the respective strings.
**Java String toCharArray(): **This method converts the string into a character array i.e first it will calculate the length of the given Java String including spaces and then create an array of char type with the same content. For example:

StringToCharArrayExample{
public static void main(String args[]){
String s1="Welcome to Edureka";
char[] ch=s1.toCharArray();
for(int i=0;i<ch.length;i++){
System.out.print(ch[i]);
}}}

The above code will return “Welcome to Edureka”.
Java StringGetBytes() : The Java string getBytes() method returns the sequence of bytes or you can say the byte array of the string. For example:

public class StringGetBytesExample {
public static void main(String args[]){
String s1="ABC";
byte[] b=s1.getBytes();
for(int i=0;i<b.length;i++){
System.out.println(b[i]);
}
}}

In the above code, it will return the value 65,66,67.
Java String IsEmpty() : This method checks whether the String is empty or not. If the length of the String is 0, it returns true else false. For example:

public class IsEmptyExample{
public static void main(String args[]) {
String s1="";
String s2="hello";
System.out.prinltn(s1.isEmpty());     // returns true
System.out.prinltn(s2.isEmpty());     // returns false
}}

In the above code, the first print statement will return true as it does not contain anything while the second print statement will return false.
Java String endsWith() : The Java String endsWith() method checks if this string ends with the given suffix. If it returns with the given suffix, it will return true else returns false. For example:

public class EndsWithExample{
public static void main(String args[]) {
String s1="hello how are you”;
System.out.println(s1.endsWith("u"));       // returns true
System.out.println(s1.endsWith("you"));     // returns true  
System.out.println(s1.endsWith("how"));     // returns false
}}

This is not the end. There are more Java String methods that will help you make your code simpler.

Moving on, Java String class implements three interfaces, namely – Serializable, Comparable and CharSequence.

Since, Java String is immutable and final, so a new String is created whenever we do String manipulation. As String manipulations are resource consuming, Java provides two utility classes: StringBuffer and StringBuilder.

Let us understand the difference between these two utility classes:
StringBuffer and StringBuilder are mutable classes. StringBuffer operations are thread-safe and synchronized whereas StringBuilder operations are not thread-safe.StringBuffer is to be used when multiple threads are working on same String and StringBuilder in the single threaded environment.StringBuilder performance is faster when compared to StringBuffer because of no overhead of synchronized.
I hope you guys are clear with Java String, how they are created, their different methods and interfaces. I would recommend you to try all the Java String examples. Do read my next blog on Java Interview Questions which will help you set apart in the interview process.

Thanks for reading

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Further reading

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Java Enum Tutorial - Enumeration in Java Explained

Java Enum Tutorial - Enumeration in Java Explained

This video on Java Enum Tutorial will provide you with detailed knowledge about Enumeration in Java along with real times examples for better understanding.

Java Enum Tutorial | Enumeration in Java Explained | Java Tutorial For Beginners

This informative video will include the following.

00:21 Agenda

00:55 What is Enum?

01:22 Why we need Enum?

06:45 Differences between Class and Enum

07:26 Syntax of Enum

07:43 Practical Examples of Enum

15:40 Advantages of using Enum

16:10 Enum Usecase: Rock Paper Scissor Game