Here's a Java program to convert a double type variable to a String:

public class Main {
    public static void main(String[] args) {
        double d = 10.5;
        String s = Double.toString(d);

        System.out.println("Double value: " + d);
        System.out.println("String value: " + s);
    }
}

In this program, we first initialize a double variable d with the value 10.5. We then use the Double.toString method to convert d to a String and assign the result to a String variable s.

Finally, we print out the original double value and the converted String value.

The output of this program will be:

Double value: 10.5
String value: 10.5

Note that the Double.toString method returns a String representation of the double value. If you need more control over the format of the String representation, you can use the String.format method instead.