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How to convert an integer to a string in Java

There are many operations which can be performed on a string but not on an integer. For example, concatenation, finding a substring, etc.

Now suppose we want to concatenate two integers or find out if an integer contains a digit; this would be a hassle if we are to only use numerical operations. However, converting an integer to a string will make things easier.

Common ways to convert an integer


1. The toString() method

This method is present in many Java classes. It returns a string. You can use it as a static function of the Integer class like this:

Integer.toString(123)

Or, use the normal version of the Integer class’ object. This cannot be used with the primitive type int, so remember to convert it to an Integer first by passing it to the constructor or simple assignment using ‘=’ operator (see the example below) :

Integer i = 123;

i.toString();

To check the type of variable, use the getClass().getName() method.

Example

public class main{
  public static void main(String[] args){
    
    // Converting 'int' to 'Integer'
    int x = 123;
    Integer y = new Integer(x); // passing to constructor

    // Integer y = x;   //  or use simple assignment

    System.out.println("Before conversion: " + y.getClass().getName());

    System.out.println("After conversion: " + y.toString().getClass().getName());
    System.out.println("After conversion (using Static method): " + Integer.toString(x).getClass().getName());
  }
}

2. String.valueOf()

Pass your integer (as an int or Integer) to this method and it will return a string:

String.valueOf(Integer(123));

Example

public class main{
  public static void main(String[] args){
    
    Integer i = new Integer(123);

    System.out.println("Before conversion: " + i.getClass().getName());
    
    System.out.println("After conversion: " + String.valueOf(i).getClass().getName());
  }
}

3. StringBuffer or StringBuilder

These two classes build a string by the append() method. We create an object of one of these two classes and call this method by passing our integer:

Example

public class main{
  public static void main(String[] args){
    
    Integer i = new Integer(123);
    StringBuilder sb = new StringBuilder(); // or StringBuffer
    sb.append(i);

    System.out.println(sb);
  }
}

4. Indirect ways


String.format("%d", int)

The first argument is any string containing %d. The second argument is the integer you want to convert. This method will replace %d with your integer. This method is not solely meant for the purpose of conversion:

String.format("%d", 100);

Example

public class main{
  public static void main(String[] args){
    
    Integer i = new Integer(123);

    System.out.println("Before conversion: " + i.getClass().getName());
    
    System.out.println("After conversion: " + String.format("%d", i).getClass().getName());
  }
}

Concatenation with an empty string

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Concatenation is also not meant for conversion, but you can concatenate your integer to an empty string because when you add an integer to a string, the result is a string:

String str = "" + 123;

Example

public class main{
  public static void main(String[] args){
    
    Integer i = new Integer(123);

    System.out.println("Before conversion: " + i.getClass().getName());
    
    System.out.println("After conversion: " + ("" + i).getClass().getName());
  }
}

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