DEV Community: Gaurav Kukade

How To Convert double To int In Java?

Gaurav Kukade — Thu, 04 Mar 2021 19:30:27 +0000

This article is originally published at https://coderolls.com/convert-double-to-int/

In this article, we will see how we can convert a double to an int.

In java programming, you will have a double primitive value (ex 82.14), but to do the further operations you need an int value (ex. 82) so let's see how to convert double to int in java.

There are three ways you can convert double to int. I will list them all below and, then we will see them one by one.

convert double to int - using typecasting
convert double to int - using Math.round()
convert double to int - using Double.IntValue()

You may like to visit:
How To Convert An Integer To String In Java

1. convert double to int - using typecasting

We know double is a 64-bit primitive value, and int is a 32-bit primitive value. So, to convert double to int, we can downcast the double value to int.

I have given a simple example below that shows to convert double to int using typecasting.

/**
 * A java program to convert double to int using typecasting 
 * @author Gaurav Kukade at coderolls.com
 **/
public class DoubleToIntUsingTypecasting{

     public static void main(String []args){

        double doubleValue = 82.14; // 82.14

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

        //typecase double to int
        int intValue = (int) doubleValue; // 82

        System.out.println("intValue: "+intValue);
     }
}

Output:

doubleValue: 82.14
intValue: 82

The problem with the typecasting is that it will truncate the value after the decimal point. It will not round it.

In the case of 82.14, we will get an int value of 82, which looks ok. But when we have a double value like 82.99, we will get only 82 and loss the 0.99 that is ~1.

It may create an issue in your calculations.

In the case of 82.99, it should be rounded to 83 and then converted to int.

It is not possible with typecasting, but our next solution can achieve it.

2. convert double to int - using `Math.round()`

Math.round() method will round the floating-point value to the nearest long value. Then we can typecast it to the int.

I have given a simple java program below that shows how to convert double to int using the Math.round() method.

/** 
 * A java program to convert double to int using 
 * Math.round() method 
 * @author Gaurav Kukade at coderolls.com
 **/
public class DoubleToIntUsingRoundMethod{

     public static void main(String []args){

        // case 1
        double doubleValue = 82.14; // 82.14

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

        //typecase double to int
        int intValue = (int) Math.round(doubleValue); // 82

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

        System.out.println();

        // case 2
        double nextDoubleValue = 82.99; // 


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

        // Math.round(nextDoubleValue) returns long value
        //typecase long to int
        int nextIntValue = (int) Math.round(nextDoubleValue); // 83

        System.out.println("nextIntValue: "+nextIntValue);              
     }
}

Output:

doubleValue: 82.14
intValue: 82

nextDoubleValue: 82.99
nextIntValue: 83

3. convert double to int - using `Double.intValue()`

In this way, we will convert the double primitive value to the Double wrapper class, and then we can use the intValue() method of the Double wrapper class.

This method does not round the value before converting it to the int value. It will remove the digits after the decimal point.

I have given a simple java program below that shows how to convert double to int using the Double.IntValue() method.

/**
 * 
 * A java program to convert double to int using 
 * Double.intValue() method  
 * @author Gaurav Kukade at coderolls.com
 * 
 **/
public class DoubleToIntUsingIntValueMethod{

     public static void main(String []args){

        double doubleValue = 82.14; // 82.14

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

        //create Double wrapper object
        Double doubleValueObject = new Double(doubleValue);


        //typecase double to int
        int intValue = doubleValueObject.intValue(); // 82

        System.out.println("intValue: "+intValue);
     }
}

Output:

doubleValue: 82.14
intValue: 82

Conclusion

We can convert double to int in java using the three ways given below.

1. convert double to int - using typecasting

In this method we typecast the double value to int as give below,

int intValue = (int) Math.round(doubleValue);

But in this way, we will lose the value after the decimal point. It will not do the rounding before converting double to int.

2. convert double to int - using Math.round()

In this way, we use the Math.round() method for the rounding purpose.

Math.round() method round the double value to the nearest long, and then we can typecast long to the int as given below.

int nextIntValue = (int) Math.round(nextDoubleValue);

3. convert double to int - using Double.IntValue()

In this way, we convert the double value to the Double wrapper class, and then we use the Double.intValue() method to get the int value.

//create Double wrapper object
Double doubleValueObject = new Double(doubleValue);

//typecase double to int
int intValue = doubleValueObject.intValue();

In this way also we will lose the digits after the decimal points.

So this is how we do convert a double to int in java. You can check all three (DoubleToIntUsingTypecasting.java, DoubleToIntUsingRoundMethod.java, DoubleToIntUsingIntValueMethod.java) programs on GitHub

You can read more about string to int and int to string conversion.

You can visit my YouTube channel 'coderolls' to find more video tutorials.

If you found this article worth, support me by giving a cup of Coffee ☕

How To Parse JSON In Java?

Gaurav Kukade — Sat, 09 Jan 2021 06:04:54 +0000

In this article we will see, how to parse JSON in java. We will be using the JSON Libraries like JSON-java, GSON and json-simple

JSON stands for JavaScript Object Notation. It is easy to use and lightweight open standard file format for storing and transporting data.

As per the json.org,

It is easy for humans to read and write. It is easy for machines to parse and generate.

Example JSON:

{
  "name": "coderolls",
  "type": "blog",
  "address": {
    "street": "1600 Pennsylvania Avenue NW",
    "city": "Washington",
    "state": "DC"
  },
  "employees": [
    {
      "firstName": "John",
      "lastName": "Doe"
    },
    {
      "firstName": "Anna",
      "lastName": "Smith"
    },
    {
      "firstName": "Peter",
      "lastName": "Jones"
    }
  ]
}

In the above JSON, name is key and coderolls is it's value. For address key, value is another JSON object which contains key and values.

For employees key, it's value is array of JSON objects.

Today we will see three json libraries in java to parse a JSON string. These are listed below,

JSON-Java
GSON
json-simple

Now we will see one by one example of all three libraries for parsing a JSON in java.

How to parse JOSN in Java using JSON-Java

JSON-java is one of the most simple JSON library for Java.

Here, we will be using the JSONObject class of the JSON-java library.

JSONObject has a constructor which accepts string. We will be using ths constructor to parse a JSON string.

public JSONObject(String source) throws JSONException

Construct a JSONObject from a source JSON text string. This is the most commonly used JSONObject constructor.

Parameters:

source  - A string beginning with  `{` (left brace)  and ending with  `}`  (right brace).

Throws:

JSONException  - If there is a syntax error in the source string or a duplicated key.

You can refer JSON-java Docs.

Maven:

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20201115</version>
</dependency>

Gradle:

compile group: 'org.json', name: 'json', version: '20201115'

Example:

package com.coderolls.JSONExample;

import org.json.JSONArray;
import org.json.JSONObject;

/**
 * A program to parse JSON strin in Java using JSON-Java
 * @author Gaurav Kukade at coderolls.com
 */

public class ParseJSONUsingJSONJava {

    public static void main(String[] args) {

        String jsonString = "{"
                + "  \"name\": \"coderolls\","
                + "  \"type\": \"blog\","
                + "  \"address\": {"
                + "    \"street\": \"1600 Pennsylvania Avenue NW\","
                + "    \"city\": \"Washington\","
                + "    \"state\": \"DC\""
                + "  },"
                + "  \"employees\": ["
                + "    {"
                + "      \"firstName\": \"John\","
                + "      \"lastName\": \"Doe\""
                + "    },"
                + "    {"
                + "      \"firstName\": \"Anna\","
                + "      \"lastName\": \"Smith\""
                + "    },"
                + "    {"
                + "      \"firstName\": \"Peter\","
                + "      \"lastName\": \"Jones\""
                + "    }"
                + "  ]"
                + "}";

        System.out.println("Parsing the json string in java using JSON-Java......\n");

        //add jsonString to the constructor
        JSONObject coderollsJSONObject = new JSONObject(jsonString);

        //now we can access the values 
        String name = coderollsJSONObject.getString("name");
        System.out.println("Name: "+name+"\n");

        //we can get the JSON object present as value of any key in the parent JSON
        JSONObject addressJSONObject = coderollsJSONObject.getJSONObject("address");

        //access the values of the addressJSONObject 
        String street = addressJSONObject.getString("street");
        System.out.println("Street: "+street+"\n");


        //we can get the json array present as value of any key in the parent JSON
        JSONArray employeesJSONArray = coderollsJSONObject.getJSONArray("employees");
        System.out.println("Printing the employess json array: \n"+employeesJSONArray.toString()+"\n");

        //we can get individual json object at an index from the employeesJSONArray
        JSONObject employeeJSONObject = employeesJSONArray.getJSONObject(0);
        String firstName = employeeJSONObject.getString("firstName");
        System.out.println("First Name of the employee at index 0: "+firstName);
    }
}

Get the code for ParseJSONUsingJSON.Java

Output:

Parsing the json string in java using JSON-Java......

Name: coderolls

Street: 1600 Pennsylvania Avenue NW

Printing the employess json array: 
[{"firstName":"John","lastName":"Doe"},{"firstName":"Anna","lastName":"Smith"},{"firstName":"Peter","lastName":"Jones"}]

First Name of the employee at index 0: John

How to parse JOSN in Java using Gson

Gson is an open-source Java library to serialize and deserialize Java objects to JSON developed at Google.

So we can use it to convert a JSON string to an equivalent Java object.

Here, we will be using the JsonObject class of the Gson library.

You can refer the docs of JsonObject.

Maven:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
</dependency>

Gradle:

compile group: 'com.google.code.gson', name: 'gson', version: '2.8.6'

Example:

package com.coderolls.JSONExample;

import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;

/**
 * A program to parse JSON strin in Java using Gson
 * @author Gaurav Kukade at coderolls.com
 */

public class ParseJSONUsingGSON {

    public static void main(String[] args) {

        //take json as string
        String jsonString = "{"
                + "  \"name\": \"coderolls\","
                + "  \"type\": \"blog\","
                + "  \"address\": {"
                + "    \"street\": \"1600 Pennsylvania Avenue NW\","
                + "    \"city\": \"Washington\","
                + "    \"state\": \"DC\""
                + "  },"
                + "  \"employees\": ["
                + "    {"
                + "      \"firstName\": \"John\","
                + "      \"lastName\": \"Doe\""
                + "    },"
                + "    {"
                + "      \"firstName\": \"Anna\","
                + "      \"lastName\": \"Smith\""
                + "    },"
                + "    {"
                + "      \"firstName\": \"Peter\","
                + "      \"lastName\": \"Jones\""
                + "    }"
                + "  ]"
                + "}";
        System.out.println("Parsing the json string in java using Gson......\n");

        Gson gson = new Gson();

        //get json object from the json string
        JsonObject coderollsJsonObject = gson.fromJson(jsonString, JsonObject.class);

        //now we can access the values 
        String name = coderollsJsonObject.get("name").getAsString();
        System.out.println("Name: "+name+"\n");

        //we can get the JSON object present as value of any key in the parent JSON
        JsonObject addressJsonObject = coderollsJsonObject.get("address").getAsJsonObject();

        //access the values of the addressJSONObject 
        String street = addressJsonObject.get("street").getAsString();
        System.out.println("Street: "+street+"\n");


        //we can get the json array present as value of any key in the parent JSON
        JsonArray employeesJsonArray = coderollsJsonObject.get("employees").getAsJsonArray();
        System.out.println("Printing the employess json array: \n"+employeesJsonArray.toString()+"\n");

        //we can get individual json object at an index from the employeesJSONArray
        JsonObject employeeJsonObject = employeesJsonArray.get(0).getAsJsonObject();
        String firstName = employeeJsonObject.get("firstName").getAsString();
        System.out.println("First Name of the employee at index 0: "+firstName);
    }
}

Get the code for ParseJSONUsingGSON.java

Output:

Parsing the json string in java using Gson......

Name: coderolls

Street: 1600 Pennsylvania Avenue NW

Printing the employess json array: 
[{"firstName":"John","lastName":"Doe"},{"firstName":"Anna","lastName":"Smith"},{"firstName":"Peter","lastName":"Jones"}]

First Name of the employee at index 0: John

How to parse JOSN in Java using json-simple

JSON.simple is a simple Java toolkit for JSON. You can use JSON.simple to encode or decode JSON text.

Maven:

<dependency>
    <groupId>com.googlecode.json-simple</groupId>
    <artifactId>json-simple</artifactId>
    <version>1.1.1</version>
</dependency>

Gradle:

compile group: 'com.googlecode.json-simple', name: 'json-simple', version: '1.1.1'

You can refer the json-simple project page.java.

Example:

package com.coderolls.JSONExample;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

/**
 * A program to parse JSON strin in Java using json-simple
 * @author Gaurav Kukade at coderolls.com
 */

public class ParseJSONUsingJsonSimple {

    public static void main(String[] args) {
        //take json as string
        String jsonString = "{"
                        + "  \"name\": \"coderolls\","
                        + "  \"type\": \"blog\","
                        + "  \"address\": {"
                        + "    \"street\": \"1600 Pennsylvania Avenue NW\","
                        + "    \"city\": \"Washington\","
                        + "    \"state\": \"DC\""
                        + "  },"
                        + "  \"employees\": ["
                        + "    {"
                        + "      \"firstName\": \"John\","
                        + "      \"lastName\": \"Doe\""
                        + "    },"
                        + "    {"
                        + "      \"firstName\": \"Anna\","
                        + "      \"lastName\": \"Smith\""
                        + "    },"
                        + "    {"
                        + "      \"firstName\": \"Peter\","
                        + "      \"lastName\": \"Jones\""
                        + "    }"
                        + "  ]"
                        + "}";

        System.out.println("Parsing the json string in java using json-simple......\n");

        JSONParser parser = new JSONParser();
        JSONObject coderollsJSONObject = new JSONObject();
        try {
            coderollsJSONObject = (JSONObject) parser.parse(jsonString);
        } catch (ParseException e) {
            e.printStackTrace();
        }

        //now we can access the values 
        String name = (String) coderollsJSONObject.get("name");
        System.out.println("Name: "+name+"\n");

        //we can get the JSON object present as value of any key in the parent JSON
        JSONObject addressJSONObject = (JSONObject) coderollsJSONObject.get("address");

        //access the values of the addressJSONObject 
        String street = (String) addressJSONObject.get("street");
        System.out.println("Street: "+street+"\n");


        //we can get the json array present as value of any key in the parent JSON
        JSONArray employeesJSONArray = (JSONArray) coderollsJSONObject.get("employees");
        System.out.println("Printing the employess json array: \n"+employeesJSONArray.toString()+"\n");

        //we can get individual json object at an index from the employeesJSONArray
        JSONObject employeeJSONObject = (JSONObject) employeesJSONArray.get(0);
        String firstName = (String) employeeJSONObject.get("firstName");
        System.out.println("First Name of the employee at index 0: "+firstName);
    }
}

Get the code for ParseJSONUsingJsonSimple.java

Output:

Parsing the json string in java using json-simple......

Name: coderolls

Street: 1600 Pennsylvania Avenue NW

Printing the employess json array: 
[{"firstName":"John","lastName":"Doe"},{"firstName":"Anna","lastName":"Smith"},{"firstName":"Peter","lastName":"Jones"}]

First Name of the employee at index 0: John

Conclusion

All three libraries allow you create a JSON object from the json string but I found the JSON-Java is easy to use.

This blogpost is already published at : https://coderolls.com/parse-json-in-java/

You can visit my YouTube channel 'coderolls' to find more video tutorials.

You can support me by giving a cup of Coffee ☕

How To Create UUID in Java?

Gaurav Kukade — Thu, 24 Dec 2020 03:52:16 +0000

In this article you will see, how to create UUID in Java.

Introduction

UUID, a universally unique identifier is a 128-bit number used to identify information in computer systems.

UUID is made of hex digits along with 4 hyphen ("-") symbols. The length of a UUID is 36 characters.

There are 5 types of UUID but mostly version 4 i.e. Randomly Generated UUID is used.

We are going to create the version 4 UUID here.

Example UUID

df6fdea1-10c3-474c-ae62-e63def80de0b

How to create UUID in Java?

Creating a Randomly Generated UUID (version 4) is really easy in Java.

UUID Class is present in java.util package. And it has the static method randomUUID() which returns the randomly generated UUID.

The example is given below.

import java.util.UUID;

/**
 * A Java program to create a Randomly Generated UUID i.e. Version 4 UUID
 * @author Gaurav Kukade at coderolls.com
 *
 */
public class CreateUUID {

    public static void main(String[] args) {

        // creating random uuid i.e. version 4 UUID
        UUID uuid = UUID.randomUUID();

        System.out.println("Printing the randomly generated UUID value......\n");

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

    }

}

Output

Printing the randomly generated UUID value......

uuid: e3aed661-ccc2-42fd-ad69-734fee350cd2

Get the above code as GitHub Gist.

This article was originally published at https://coderolls.com/create-uuid-in-java/

You can visit my YouTube channel 'coderolls' to find more video tutorials.

How do you name your GIT branch?

Gaurav Kukade — Mon, 13 Jan 2020 11:44:48 +0000

Hi developers,

I will like to ask you a simple question.

How do you name your GIT branch?

A. b/your_new_branch_name
B. your_new_branch_name

I am using the first way at my organization. Why I am doing this? 🤔 Because I have observed all are doing the same. 😐

My colleague told me that we are using 'b/' to identify it as a branch easily.

What do you think about it?

Please write down your opinion on the branch names in the comment section below.

Thanks!

8 Basic GIT Commands Every Newbie Developer Must Know

Gaurav Kukade — Mon, 30 Dec 2019 07:39:28 +0000

GIT is one of the most important parts of the developer's day to day work. So learning GIT is a must for a newbie developer. In this article, you are going to learn the 8 most important basic GIT commands.

Below, I have listed down all the 8 commands and then, we will have a look at them one by one.

git init
git clone
git add
git commit
git status
git branch
git pull
git push

1. `git init`

git init command initializes brand new GIT repository (locally) and begins tracking the existing directory.

When you hit the git init command, git adds a subfolder withing an existing directory that manages all required files for version controlling.

HP@Gaurav MINGW64 /e/example
$ git init
Initialized empty Git repository in E:/example/.git/

HP@Gaurav MINGW64 /e/example (master)
$

You are hitting git init means you want to initialize the current directory as GIT repository.

The following GIF files show initializing a new repository and a hidden sub-folder containing all data structure required for version control.

2. `git clone`

git clone creates a local copy of a repository that already exists remotely. The local copy is the exact copy of the remote repository, it contains the same files, history, and branches.

$ git clone <remote-repository-link>

HP@Gaurav MINGW64 /e/directory
$ git clone https://github.com/gauravkukade/example.git
Cloning into 'example'...
remote: Enumerating objects: 16, done.
remote: Counting objects: 100% (16/16), done.
remote: Compressing objects: 100% (10/10), done.
remote: Total 16 (delta 3), reused 7 (delta 2), pack-reused 0
Unpacking objects: 100% (16/16), done.

HP@Gaurav MINGW64 /e/directory
$

You can clone any public repository from the platforms like GitHub, BitBucket, GitLab, and other GIT hosting platforms.

The following GIF shows the git clone command

3. `git add`

git add stages a change.

If you are done with changes in your code then its necessary to stage that changes and take a snapshot of it to include it in the repository's history.

git add does the first step, it stages a change.

$ git add <path-of-the-file-you-made-changes-in>

If you made changes in the multiple files and you want to stage all files in the same command then add the file path of all files separated y a single space.

$ git add <first-filepath-you-want-to-stage> <second-filepath-you-want-to-stage> <nth-filepath-you-want-to-stage>

If you want to stage all the files, then write '.' (dot) after git add

$ git add .

Any staged changes will become the part of the next snapshot and a part of the repository's history.

You can stage and take a snapshot of the current changes in a single command also but is not recommended.

Staging your changes first and then taking snapshot gives you complete control over the repository's history.

The following GIF shows the git add command

4. `git commit`

git commit save the snapshot to the repository's history.

git add does the first step i.e. staging the changes and git commit does the final step i.e. it saves the snapshot to the repository's history. In GIT these two-step completes the changes tracking process.

$ git commit -m "<meaningful-git-commit-message>

You can write a meaningful message to the commit. It is recommended to write a commit message in the 'Simple Present Tense'.

If you are committing a new feature to your project then your commit message should be "Add <feature-name> feature".

The following GIF shows the git commit command

It is the simple way to write the commit message but there is a more in-depth way to write a commit message with title and description. We will see that in a separate blogpost.

5. `git status`

git status shows the status of the changes as untracked, modified or staged.

HP@Gaurav MINGW64 /e/directory/example (master)
$ git status
On branch master
Your branch is up-to-date with 'origin/master'.

Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

        modified:   README.md

Untracked files:
  (use "git add <file>..." to include in what will be committed)

        ex.txt


HP@Gaurav MINGW64 /e/directory/example (master)
$

The following GIF shows the git status command

6. `git branch`

git branch list the existing branches from the local repository. The current branch will be highlighted in green and marked with an asterisk.

HP@Gaurav MINGW64 /e/directory/example (master)
$ git branch
* master
  new_branch

HP@Gaurav MINGW64 /e/directory/example (master)
$

The followig gif shows the git branch command

7. `git pull`

git pull update the local repository with updates from its remote counterpart. i.e. remote repository.

HP@Gaurav MINGW64 /e/directory/example (master)
$ git pull
remote: Enumerating objects: 4, done.
remote: Counting objects: 100% (4/4), done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 0
Unpacking objects: 100% (3/3), done.
From https://github.com/gauravkukade/example
   15e8755..d7aefb1  master     -> origin/master
Updating 15e8755..d7aefb1
Fast-forward
 new-file-added-to-remote-repository.txt | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 new-file-added-to-remote-repository.txt

HP@Gaurav MINGW64 /e/directory/example (master)
$

If your teammate made commits to the remote branch and you want to reflect these changes in your local environment then you will hit the command git pull.

This command will check if there are any updates on the remote branch as compared to your local environment, if yes, then it will update your local environment with these changes. If no, then it will do nothing.

The following GIF shows the git pull command

8. `git push`

git push updates the remote repository with any commits made locally to a brach

$ git push origin <branch-name-you-have made commits on>

If the branch does not exist on a remote repository then the whole branch with its commits will be pushed to the remote repository.

$ git push origin <newly-locally-created-branch-name>

HP@Gaurav MINGW64 /e/directory/example (master)
$ git push origin master
fatal: HttpRequestException encountered.
   An error occurred while sending the request.
Username for 'https://github.com': gauravkukade
Counting objects: 2, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (2/2), 255 bytes | 255.00 KiB/s, done.
Total 2 (delta 1), reused 0 (delta 0)
remote: Resolving deltas: 100% (1/1), completed with 1 local object.
To https://github.com/gauravkukade/example.git
   d7aefb1..dc3d3ef  master -> master

HP@Gaurav MINGW64 /e/directory/example (master)
$

The following GIF shows the git push command

You are here means you like the post and hence here is your bonus content.

How to create a new branch locally

You can create a new branch locally using the following command

$ git checkout -b <your-new-branch-name>

If you found this article worth, please Give me a cup of Coffee ☕

If you have queries please let me know in the comment section below.

This article originally published at https://coderolls.com/basic-git-commads/

Hi 👋🏼, I am Gaurav Kukade, a Java Developer and author at https://codeRolls.com

How Do I Compare Strings In Java

Gaurav Kukade — Fri, 20 Dec 2019 12:16:37 +0000

This article is originally published at https://coderolls.com/compare-strings-in-java/

In this article you are going to learn how to compare strings. What problem occurs when you compare string using equals to (=)operator.

Introduction

The String is a special Class in Java. We use String regularly in Java programs, so comparing two string is a common practice in Java. In this article I tried to answer the most common questions about the string, ‘How do I compare strings in Java?’

Comparing strings is very helpful the processes like authentication, sorting, reference matching, etc.

I have listed 3 ways to compare strings in Java.

Using equals() method ( comparing the content)
Using == operator (comparing the object reference)
Using compareTo() method (comparing strings lexicographically)

1. Compare strings using `equals()` method

In this way, I am using .equals() instance method of the String class. Originally .equals() method is the Object class method, String class overrides it.

**equals()** method the compare two strings for value equality, weather they are logically equal.

equals() method in String class takes another string a parameter and compare it with the specified string, it returns true if and only if the parameter string is not null and contains the same characters as the specified string.

public boolean equals(Object anObject)

It compare this string with the argument strings and return true if the argument is not null and contains the same character as the specified string.

param -
another string

returns -

true - if argument is not null and it contains same characters as the specified string
false - if the argument is null or it does not contain same characters as the specified string

ex. firstString.equals(secondString)
// returns true if and only if the secondString is not null and contains the same characters as firstString.

I have given the program to compare string using equals() method below

/**
 * A Java program to compare two strings using equsls()
 * and equalsIgnoreCase() method of the String.
 * 
 * @author Gaurav Kukade at coderolls.com
 */

public class CompareUsingEquals {

  public static void main(String[] args) {
    String firstString = "coderolls";
    String secondString = "javablog";
    String thirdString = "coderolls";
    String fourthString = "CodeRolls";

    System.out.println("Comparing strings using equals() and equalsIgnoreCase() method\n");

    // Using equals() method
    System.out.print("firstString.equals(secondString) : ");
    System.out.println(firstString.equals(secondString));

    System.out.print("firstString.equals(thirdString) : ");
    System.out.println(firstString.equals(thirdString));

    /*
     * Using equalsIgnoreCase() method to ignore
     * case consideration (i.e. Capital or small) of both the strings.
     */
    System.out.print("firstString.equalsIgnoreCase(fourthString) : ");
    System.out.println(firstString.equalsIgnoreCase(fourthString));
  }

}

Output:

Comparing strings using equals() and equalsIgnoreCase() method

firstString.equals(secondString) : false
firstString.equals(thirdString) : true
firstString.equalsIgnoreCase(fourthString) : true

2. Compare strings using `==` operator

In String, **==** operator is used to comparing the reference of the given strings, whether they are referring to the same objects.

When you compare two strings using == operator, it will return true if the string variables are pointing toward the same java object, else it will return false.

I have given a Java program to compare using == operator below

/**
 * A Java program to compare strings using == operator.
 * 
 * == operator ckecks weather both the strings referring
 * to the same String Object.
 * 
 * @author Gaurav Kukade at coderolls.com
 */

public class CompareUsingEqualsToOperator {

  public static void main(String[] args) {

    String firstString = "coderolls";
    String secondString = "javablog";
    String thirdString = "coderolls";

    // creating new String object with the same value as firstString or thirdString
    String fourthString =  new String("coderolls");

    System.out.println("Comparing strings using == operator \n");

    System.out.print("firstString == secondString : ");
    System.out.println(firstString == secondString);

    /*
     * Here firstString and thirdString is referring to the same String object
     * hence it will print 'true'.
     */
    System.out.print("firstString == thirdString : ");
    System.out.println(firstString == thirdString);

    /*
     * Here firstString and fourthString have same value
     * but they are referring to the different String object.
     * 
     * hence it will print 'false'
     */
    System.out.print("firstString == fourthString : ");
    System.out.println(firstString == fourthString);
  }

}

Output:

Comparing strings using == operator 

firstString == secondString : false
firstString == thirdString : true
firstString == fourthString : false

Problem with using `==` operator for string comparison

Most of the beginner Java developers commit this mistake by comparing two strings using the == operator.

Logically, they have to check whether both the string contains the same character sequence or not.

In Java String, the == operator used to check the reference of both the string objects and equals() method used to check the value equality of both strings.

== – checks reference equality

equals() – checks the value equality

When we assign a string value to the string variable JVM will check if the string with the equal value already present in the string pool or not. If it is not present in the string pool, it will be added to the constant pool and the reference to that string object is returned.

If it is present in the string pool, the reference to the memory address of that string object is returned.

The following image shows the pictorial explanation of the same.

‘firstString’ pointing towards the “coderolls” string in string pool

If we are assigning the equal value to another string variable, JVM checks if the string with that value is present in the string constant pool or not.

Since the string object with that value is already created in the previous step. Another string variable starts referring to the previously created string object instance.

The following image shows the pictorial explanation for the same

‘firstString’ and ‘secondString’ pointing towards the “coderolls” string in string pool

When we create string using the new operator, a new string object is created and stored in the Java heap space.

‘firstString’ and ‘secondString’ pointing towards the “coderolls” string in string pool and ‘thirdString’ pointing towards the “coderolls” in java heap space.t

3. Compare strings using `compareTo()` method

compareTo() method is used to compare two strings lexicographically. i.e. Alphabetically.

compareTo() method compares the character sequence of the argument string with the character sequence of the specified string.

Showing argument string and a specified string.

It returns a negative integer if the argument string is lexicographically greater than the specified string. i.e if the argument string follows the specified string. ( argument String > specified String )

It returns positive integer if the argument string is lexicographically smaller than the specified string. i.e. If the argument string precedes the specified string. ( argument String < specified String )

It returns zero if both the strings are lexicographical equals. ( argument String = specified String )

If you want to ignore the cases of both the string use compareToIgnoreCase() method.

I have given a program for comparing strings using the compareTo() method. It also consists a case for ignoring the cases with compareToIgnoreCase() method.

 * A Java program to compare strings using compareTo()
 * and compareToIgnoreCase() method.
 * 
 * compareTo() compare strings lexicograpgically.
 * 
 * @author Gaurav Kukade at coderolls.com
 */

public class CompareUsingCompareTo {

  public static void main(String[] args) {

    String firstString = "java";
    String secondString = "coderolls";
    String thirdString = "sql";
    String fourthString = "CodeRolls";

    System.out.println("Comparing strings using compareTo() and compareToIgnoreCase() method\n");

    // Using compareTo() method
    System.out.print("firstString.compareTo(secondString) : ");
    System.out.println(firstString.compareTo(secondString));

    System.out.print("firstString.compareTo(thirdString) : ");
    System.out.println(firstString.compareTo(thirdString));

    /*
     * Using compareToIgnoreCase() method to ignore
     * case consideration (i.e. Capital or small) of both the strings.
     */
    System.out.print("secondString.compareToIgnoreCase(fourthString) : ");
    System.out.println(secondString.compareToIgnoreCase(fourthString));
  }

}

Output:

Comparing strings using compareTo() and compareToIgnoreCase() method

firstString.compareTo(secondString) : 7
firstString.compareTo(thirdString) : -9
secondString.compareToIgnoreCase(fourthString) : 0

I have written a detailed article on how to compare strings lexicographically in java. In this article, I have also created a user-defined method to compare two strings lexicographically.

Conclusion

We can compare strings using the ways given below

Using equals() method : equals() method in the strings used to check the string value equality whether they contain the same character sequence.
Using == operator : == operator used to check the reference equality of the two strings, whether they are pointing towards the same string object.
Using compareTo() method : compareTo() method used to check the strings lexicographically. I.e alphabetically. Check the detailed articles on How to compare strings lexicographically.

Most of the beginner java developers do mistakes while comparing strings. They actually want to check the content of the string but they use == operator to check it.

It is always advised to use equals() method to compare the string on the basis of its content.

If you have any queries about the code blocks given above, please write it down in the comment section below. Also. let me know if you have any other way to compare two strings in java in the comment section.

This article is originally published at https://coderolls.com/compare-strings-in-java/

DEV Community: Gaurav Kukade

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How Do I Compare Strings In Java

Introduction

1. Compare strings using `equals()` method

2. Compare strings using `==` operator

Problem with using `==` operator for string comparison

3. Compare strings using `compareTo()` method

Conclusion

Related Article

DEV Community: Gaurav Kukade

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1. convert double to int - using typecasting

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How Do I Compare Strings In Java

Introduction

1. Compare strings using equals() method

2. Compare strings using == operator

Problem with using == operator for string comparison

3. Compare strings using compareTo() method

Conclusion

Related Article

2. convert double to int - using `Math.round()`

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1. `git init`

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4. `git commit`

5. `git status`

6. `git branch`

7. `git pull`

8. `git push`

1. Compare strings using `equals()` method

2. Compare strings using `==` operator

Problem with using `==` operator for string comparison

3. Compare strings using `compareTo()` method