Java   page 6
ccsun5 testjava > cat -n TestPrecision.java
     1	// TestPrecision.java  -- CopyLeft by tsaiwn@csie.nctu.edu.tw
     2	// to Test (1)precision, (2)computation rule for floating expression
     3	// please compare to floatdbl.c in our C/C++ handouts
     4	//Also test the format capability of the java.text.Format class
     5	//It and it's subclasses provides data editing similar to printf() in C Lang.
     6	import java.text.*;     // Format, NumberFormat, DecimalFormat, ...
     7	public class TestPrecision {
     8	   static final String f4dot2 = "0.00"; //Integer part at least one digit
     9	   private static String myformat(float x){
    10	      DecimalFormat f = new DecimalFormat(" #######00.000####");
    11	      return f.format(x);  //at least like 99.999
    12	   }
    13	   private static String myformat(double x){  // rewrite for double
    14	      DecimalFormat f = new DecimalFormat("########0.0000000");
    15	      return f.format(x);   // the above means f.setMaximumFractionDigits(7);
    16	   }
    17	   private static String myfm2(double x){
    18	      DecimalFormat f = new DecimalFormat(f4dot2);
    19	      f.setMinimumIntegerDigits(5);   // at least 5 digits in Integer part
    20	      return f.format(x);
    21	   }
    22	   public static void main( String p[])  {
    23	      float x, xdelta;
    24	      double y; long i;
    25	      x = (float)1234567.2;
    26	      xdelta = 0.0001f;
    27	      System.out.println("Before loop, x="+ x);
    28	      System.out.println("     (double)x="+ (double)x);
    29	      System.out.println("            ===" + myformat(x) );
    30	      System.out.println("xdelta="+ myformat(xdelta));
    31	      for(i=1; i<= 8000; i++){
    32	         x = x + xdelta;     /******/
    33	      }
    34	      System.out.println(" After loop, x="+ x);
    35	      System.out.println("     (double)x="+ (double)x);
    36	      System.out.println("\nDo it again with double y ...");
    37	      y = 1234567.2;
    38	      xdelta = 0.0001F;
    39	      System.out.println("Before loop, y="+ y);
    40	      System.out.println("            ===" + myformat(y) );
    41	      for(i=1; i<= 8000; i++){
    42	         y = y + xdelta;   /*** promotion is allowed, not coercion ***/
    43	      }                    /*** x = y; is not allowed ! ***/
    44	      System.out.println(" After loop, y="+ y);
    45	      System.out.println("            ===" + myformat(y) );
    46	      System.out.println(" == myfm2() has format pattern"+
    47	             " \"0.00 with modification through its method\"==");
    48	      System.out.println("      which means %4.2f in C Language");
    49	      System.out.println(" myfm2(123.564)=" + myfm2(123.564) );
    50	      System.out.println(" myfm2(123.566)=" + myfm2(123.566) );
    51	      System.out.println(" myfm2(123.565)=" + myfm2(123.565) );
    52	      System.out.println(" 注意不是真的四捨五入, 這符合IEEE754的規定");
    53	  System.out.println("3849==="+ new DecimalFormat("##000000").format(3849));
    54	   }
    55	}
ccsun5 testjava > /usr/local/jdk/jdk1.2.2/bin/javac TestPrecision.java
sjhuang has replaced srchao on pts/17 from openbsd.
ccsun5 testjava > /usr/local/jdk/jdk1.2.2/bin/java TestPrecision
Before loop, x=1234567.2
     (double)x=1234567.25
            === 1234567.250
xdelta= 00.0001
 After loop, x=1234567.2
     (double)x=1234567.25

Do it again with double y ...
Before loop, y=1234567.2
            ===1234567.2000000
 After loop, y=1234568.0000005036
            ===1234568.0000005
 == myfm2() has format pattern "0.00 with modification through its method"==
      which means %4.2f in C Language
 myfm2(123.564)=00123.56
 myfm2(123.566)=00123.57
 myfm2(123.565)=00123.56
 注意不是真的四捨五入, 這符合IEEE754的規定
3849===003849
ccsun5 testjava > exit