Java Program to Convert Int to Double

Java data types can be categorized as primitive and non-primitive. Primitive data types contain a single value, whereas non-primitive data types contain an address of the variable value. Java supports 7 primitive data types - boolean, byte, char, short, int, long, float, and double. These data types require a different amount of space while stored in memory.

Int stores 32-bit signed two’s complement integer and require 32 bits (4 bytes) to be stored in memory while double stores double-precision 64-bit floating-point numbers and require 64 bits (8 bytes) for storage. Many times int values need to be converted to double so, to perform such conversion following three methods can be used:

• Conversion using assignment operator or Implicit Conversion
• Conversion using Double class constructor
• Conversion using valueOf() method

1. Conversion using an Assignment Operator

Java performs implicit conversion or widening conversion when both data types involved in conversion are compatible, or the value of a smaller data type is assigned to a bigger data type. Double is bigger than int as it requires more storage space; hence, int values are implicitly converted to double by Java.

Syntax:

double d = i

Here,

• d = variable to store double value after conversion to double data type
• i = integer value to be converted to double data type

// Java program to convert int to 
// double using assignment operator

class GFG {
    public static void main(String[] args)
    {
        int i = 100;
        // Implicit conversion from int to double data type
        double d = i;

        System.out.println("Integer value " + i);
        System.out.println("Double value " + d);
    }
}

Integer value 100
Double value 100.0

2. Conversion using Double Wrapper Class Constructor

Double class in Java is a wrapper class used to create objects that can hold single, double type values and contain several methods to deal with double matters. Int value can be passed to the constructor of the Double class to create an object of double type initialized with provided integer value.

Syntax:

Double d = new Double(i)

Here,

• d = variable to store double value after conversion to double data type
• i = integer value to be converted to double data type

// Java program to convert int to double 
// using Double wrapper class constructor

class GFG {
    public static void main(String[] args)
    {
        int i = 100;
        // Conversion of int to double data 
          //type using Double wrapper class
        Double d = new Double(i);

        System.out.println("Integer value " + i);
        System.out.println("Double value " + d);
    }
}

Output

Integer value 100
Double value 100.0

3. Conversion using valueOf() Method of Double Wrapper Class

Double wrapper class valueOf() method converts int value to double type. It returns the Double-object initialized with the provided integer value. 

Syntax: 

Double d = Double.valueOf(i)

Here,

• d = variable to store double value after conversion to double data type
• i = integer value to be converted to double data type

// Java program to convert int 
// to double using valueOf() method

class GFG {
    public static void main(String[] args)
    {
        int i = 100;
        // Conversion of int to double data type using valueOf() method
        Double d = Double.valueOf(i);

        System.out.println("Integer value " + i);
        System.out.println("Double value " + d);
    }
}

Integer value 100
Double value 100.0

Example to Convert int[] array to a double[] array

To convert an int[] array to double[] array , we can iterate through the int array and cast each value to double.

// Java program to convert 
// int[] array into double[] array
public class Geeks {
    public static void main(String[] args) {
      
        // Initialize the int array
        int[] arr = { 1, 2, 3, 4, 5 };
      
        // Convert int array to double array 
        // using toDoubleArray method
        double[] darr = toDoubleArray(arr);

        for (double d : darr) {
            System.out.print(d + " ");
        }
    }

    // Method to convert int array to double array
    public static double[] toDoubleArray(int[] arr)
    {
        // Create a new double array with the 
        // same length as the int array
        double[] darr = new double[arr.length];
      
        // Loop through the int array and 
        // convert each element to double
        for (int i = 0; i < arr.length; i++) {
          
            // Cast int element to double
            darr[i] = (double)arr[i];
        }
        return darr;
    }
}

1.0 2.0 3.0 4.0 5.0