In Java, you can convert an int type variable to a double type variable using a type casting operation. Here's an example:

int num = 10;
double d = (double) num;

System.out.println("Double value: " + d); // output: 10.0

In the above example, we define an int variable num with a value of 10. We then use type casting to convert num to a double variable d. The (double) expression is used to tell the Java compiler to treat the int value as a double.

After the conversion, the value of d is 10.0, which we verify by printing it to the console using the System.out.println method.

Note that when converting an int to a double, the resulting value is a floating-point number with a decimal point and a trailing zero. If the int value represents a large number, it may result in a loss of precision when converting to a double.