Java: 0 supplement to 6 digits

import java.text.*;

System.out.println("0 Supplement");
String txtSEQ_NO = "123";
double dSEQ_NO = Double.parseDouble(txtSEQ_NO);
DecimalFormat d1 = new DecimalFormat("000000");
System.out.println("d1 = " + d1.format(dSEQ_NO));
String a = String.valueOf(d1.format(dSEQ_NO));
System.out.println("a = " + a);