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How To Nail Your Next Tech Interview

How to Convert an Integer to a String in Java
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How to Convert an Integer to a String in Java

Java is one of the most preferred programming languages. Software developers or engineers preparing for coding interviews should make it a point to review some of the basics of Java as a part of their prep. In this article, we’ll look at how an integer can be converted into a string in Java. This process can come in handy while solving problems at tech interviews.

Here’s what we’ll cover:

  1. Introduction
  2. 5 Different methods to convert integer to string in Java 
  3. Java interview questions on converting an integer to a string

Introduction

String in Java is a collection of characters, and there are many operations, such as finding substring and concatenation, that can be performed on a string but not on an integer. Say we want to concatenate two integers or want to find out if an integer contains a specific digit or not. We can simply convert integers to strings to do this type of operation easily. 

Different Methods to Convert an Integer to String in Java

There are many ways to convert integers to strings; let's look at them one by one. 

Method 1. Using toString() Method

The return type of to String() is String, and it is present in many Java classes.  

It can be used in two ways:

  1. By the static function of the Integer class like Integer.toString(100)
  2. By using the regular version of the Integer class’s object. We need first to convert int to Integer because this method cannot be used with the primitive type int. We can use a simple assignment using the = operator. 

Here’s the code:

public class IK{

  public static void main(String[] args){    

    Integer n = new Integer(100); // Passing int to constructor. 

    System.out.println("Before conversion: " + n);    

    // Object res to store the result. 

    String result = n.toString();    

    System.out.println("After conversion: " + result);

  }

}

Output: 

Before conversion: 100
After conversion: 100

Method 2: Using String.valueOf()

This method is used to return the string representation of passed Integer (int or Integer)

Example: String.valueOf(Integer(100));

Here is how it’s implemented:

public class IK{

  public static void main(String[] args){    

    Integer n = new Integer(100); // Passing int to constructor. 

    System.out.println("Before conversion: " + n);    

    // Object res to store the result. 

    String result = String.valueOf(n);    

    System.out.println("After conversion: " + result );

  }

}


Output: 

Before conversion: 100
After conversion: 100

Method 3: Using StringBuilder

StringBuilder class can be used to convert Integer to the string; this class builds a string by calling the append() method in it. We will create an object of StringBuilder and call method append() by passing out Integer. Then we can use the toString() method to get the answer in the String object. 

The following is the code:

public class IK{

  public static void main(String[] args){    

    Integer n = new Integer(100); // Passing int to constructor. 

    System.out.println("Before conversion: " + n);    

    // Creating StringBuilder object s

    StringBuilder s = new StringBuilder(); 

    // Passing Integer to append() method

    s.append(n);

    // Object res to store the result. 

    String res = s.toString();    

    System.out.println("After conversion: " + res);

  }

}


Output: 

Before conversion: 100
After conversion: 100

Method 4 (Indirect Way): Using String.format()

Syntax of this method is String.format("%d", int). Here, the first argument is any string containing %d

%d stands for integer, which means the passed parameter is integer here. The second argument is the integer we want to convert. This method will return the String object containing a string representation of our number. 

Here’s the code:

public class IK{

  public static void main(String[] args){    

    Integer n = new Integer(100); // Passing int to constructor. 

    System.out.println("Before conversion: " + n);    

    // Object res to store the result. 

    String res = String.format("%d", n);    

    System.out.println("After conversion: " + res);

  }

}

Output: 

Before conversion: 100
After conversion: 100

Method 5 (Indirect Way): Using Concatenation With Empty String

In Java, we can simply concatenate an Integer to an empty string, and it will give a String representation of our Integer. 

Here’s how:

public class IK{

  public static void main(String[] args){    

    Integer n = new Integer(100); // Passing int to constructor. 

    System.out.println("Before conversion: " + n);    

    // Object res to store the result. 

    String res = "" + n;    

    System.out.println("After conversion: " + res);

  }

}

Output: 

Before conversion: 100
After conversion: 100

Interview Questions on Converting Integer to String in Java

Here are a few sample interview questions related to converting an integer to a string in Java: 

  1. How to convert string to int in Java?
  2. How to convert int to string in Java effectively?
  3. Why is string immutable in Java?
  4. How to convert char to integer in Java?
  5. How to convert integer to char in Java?
  6. How to convert char array to string in Java?
  7. How to convert double to string in Java?

Recommended Reading

Check out our learn page for more articles on Java:

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---------

Article contributed Omkar Deshmukh

Last updated on: 
October 27, 2023
Author

Abhinav Rawat

Product Manager @ Interview Kickstart | Ex-upGrad | BITS Pilani. Working with hiring managers from top companies like Meta, Apple, Google, Amazon etc to build structured interview process BootCamps across domains

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How to Convert an Integer to a String in Java

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