You can convert variables from one data type to another in Java using different methods.

In this article, you'll learn how to convert integers to strings in Java in the following ways:

  • Using the Integer.toString() method.
  • Using the String.valueOf() method.
  • Using the String.format() method.
  • Using the DecimalFormat class.

How to Convert an Integer to a String in Java Using Integer.toString()

The Integer.toString() method takes in the integer to be converted as a parameter. Here's what the syntax looks like:

Integer.toString(INTEGER_VARIABLE)

Here's an example:

class IntToStr {
    public static void main(String[] args) {
        
        int age = 2;
        String AGE_AS_STRING = Integer.toString(age);
        
        System.out.println("The child is " + AGE_AS_STRING + " years old");
        // The child is 2 years old
    }
}

In the example above, we created an integer – age – and assigned a value of 2 to it.

To convert the age variable to a string, we passed it as a parameter to the Integer.toString() method: Integer.toString(age).

We stored this new string value in a string variable called AGE_AS_STRING.

We then concatenated the new string variable with other strings: "The child is " + AGE_AS_STRING + " years old".

But, would an error be raised if we just concatenated the age variable to these other strings without any sort of conversion? 

class IntToStr {
    public static void main(String[] args) {
        
        int age = 2;
        
        System.out.println("The child is " + age + " years old");
        // The child is 2 years old
    }
}

The output above is the same as the example where we had to convert the integer to a string.

So how do we know if the type conversion actually worked?

We can check variable types using the Java getClass() object. That is: 

class IntToStr {
    public static void main(String[] args) {
        
        int age = 2;
        
        String AGE_AS_STRING = Integer.toString(age);
        
        
        System.out.println(((Object)age).getClass().getSimpleName());
        // Integer
        
        System.out.println(AGE_AS_STRING.getClass().getSimpleName());
        // String
    }
}

Now we can verify that when the age variable was created, it was an Integer, and after type conversion, it became a String.

How to Convert an Integer to a String in Java Using String.valueOf()

The String.valueOf() method also takes the variable to be converted to a string as its parameter. 

class IntToStr {
    public static void main(String[] args) {
        
        int age = 2;
        
        String AGE_AS_STRING = String.valueOf(age);
        
        System.out.println("The child is " + AGE_AS_STRING + " years old");
        // The child is 2 years old
    }
}

The code above is similar to that in the last section:

  • We created an integer called age.
  • We passed the age integer as a parameter to the String.valueOf() method: String.valueOf(age).

You can also check to see if the type conversion worked using the getClass() object: 

System.out.println(((Object)age).getClass().getSimpleName());
// Integer
        
System.out.println(AGE_AS_STRING.getClass().getSimpleName());
// String

How to Convert an Integer to a String in Java Using String.format()

The String.format() method takes in two parameters: a format specifier and the variable to be formatted.

Here's an example: 

class IntToStr {
    public static void main(String[] args) {
        
        int age = 2;
        
        String AGE_AS_STRING = String.format("%d", age);
        
        System.out.println("The child is " + AGE_AS_STRING + " years old");
        // The child is 2 years old
        
    }
}

In the example above, we passed in two parameters to the String.format() method: "%d" and age.

"%d" is a format specifier which denotes that the variable to be formatted is an integer.

age, which is the second parameter, will be converted to a string and stored in the AGE_AS_STRING variable.

You can also check the variable types before and after conversion: 

System.out.println(((Object)age).getClass().getSimpleName());
// Integer
        
System.out.println(AGE_AS_STRING.getClass().getSimpleName());
// String

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

The DecimalFormat class is used for formatting decimal numbers in Java. You can use it in different ways, but we'll be using it to convert an integer to a string.

Here's an example:

import java.text.DecimalFormat;

class IntToStr {
    public static void main(String[] args) {
        
        int age = 2;
        
        DecimalFormat DFormat = new DecimalFormat("#");
        
        
        String AGE_AS_STRING = DFormat.format(age);
        
        System.out.println("The child is " + AGE_AS_STRING + " years old");
        // The child is 2 years old
        
        
        System.out.println(((Object)age).getClass().getSimpleName());
        // Integer
        
        System.out.println(AGE_AS_STRING.getClass().getSimpleName());
        // String
        
    }
}

Let's break the code down:

  • To be able to use the DecimalFormat class in the example above, we imported it: import java.text.DecimalFormat;.
  • We created the integer age variable.
  • We then created a new object of the DecimalFormat class called DFormat.
  • Using the object's format() method, we converted age to a string: DFormat.format(age);.

Summary

In this article, we talked about converting integers to strings in Java.

We saw examples that showed how to use three different methods – Integer.toString(), String.valueOf(), String.format() — and the DecimalFormat class to convert variables from integers to strings.

Each example showed how to check the data type of a variable before and after conversion.

Happy coding!