// TestPrecision.java  -- CopyLeft by tsaiwn@csie.nctu.edu.tw
// to Test (1)precision, (2)computation rule for floating expression
// please compare to floatdbl.c in our C/C++ handouts
//Also test the format capability of the java.text.Format class
//It and it's subclasses provides data editing similar to printf() in C Lang.
import java.text.*;     // Format, NumberFormat, DecimalFormat, ...
public class TestPrecision {
   static final String f4dot2 = "0.00"; //Integer part at least one digit
   private static String myformat(float x){
      DecimalFormat f = new DecimalFormat(" #######00.000####");
      return f.format(x);  //at least like 99.999
   }
   private static String myformat(double x){  // rewrite for double
      DecimalFormat f = new DecimalFormat("########0.0000000");
      return f.format(x);   // the above means f.setMaximumFractionDigits(7);
   }
   private static String myfm2(double x){
      DecimalFormat f = new DecimalFormat(f4dot2);
      f.setMinimumIntegerDigits(5);   // at least 5 digits in Integer part
      return f.format(x);
   }
   public static void main( String p[])  {
      float x, xdelta;
      double y; long i;
      x = (float)1234567.2;
      xdelta = 0.0001f;
      System.out.println("Before loop, x="+ x);
      System.out.println("     (double)x="+ (double)x);
      System.out.println("            ===" + myformat(x) );
      System.out.println("xdelta="+ myformat(xdelta));
      for(i=1; i<= 8000; i++){
         x = x + xdelta;     /******/
      }
      System.out.println(" After loop, x="+ x);
      System.out.println("     (double)x="+ (double)x);
      System.out.println("\nDo it again with double y ...");
      y = 1234567.2;
      xdelta = 0.0001F;
      System.out.println("Before loop, y="+ y);
      System.out.println("            ===" + myformat(y) );
      for(i=1; i<= 8000; i++){
         y = y + xdelta;   /*** promotion is allowed, not coercion ***/
      }                    /*** x = y; is not allowed ! ***/
      System.out.println(" After loop, y="+ y);
      System.out.println("            ===" + myformat(y) );
      System.out.println(" == myfm2() has format pattern"+
             " \"0.00 with modification through its method\"==");
      System.out.println("      which means %4.2f in C Language");
      System.out.println(" myfm2(123.564)=" + myfm2(123.564) );
      System.out.println(" myfm2(123.566)=" + myfm2(123.566) );
      System.out.println(" myfm2(123.565)=" + myfm2(123.565) );
      System.out.println(" 注意不是真的四捨五入, 這符合IEEE754的規定");
  System.out.println("3849==="+ new DecimalFormat("##000000").format(3849));
   }
}