conversion : Java Glossary

I have also written the Conversion Amanuensis Applet in Java, available with source code, that will generate Java source code for any of the 400 possible conversions between the 20 basic types. You can then cut and paste the result into your code.

Primitives

Primitives vs Immutable Wrapper Objects

Truncation

byte[] ⇔ String

String s = "abc";

// string -> byte[]
byte [] b = s.getBytes( "8859_1" /* encoding */ );

// byte[] -> String
String t = new String( byteArray, "Cp1252" /* encoding */ );

// subset of byte[] -> String
String t = new String( byteArray, offset, length, "UTF-8" /* encoding */ );

char[] ⇔ String

String s = "abc" ;
// string -> char[]
char[] ca = s.toCharArray();
// char[] -> String
String s = new String( ca );

Beware of char[].toString(). It does not convert the character array to String. It prints out the address of the array — not useful for anything. Use new String ( chararray ) instead.

Hexadecimal

StringBuffers & StringBuilders

Rounding

// Rounding to an integer:
long n = Math.round(d);
double d = Math.rint(d);

// Rounding to two decimal places:
long n = Math.round(d *100.); /* keep as "pennies" */
double d = Math.rint (d *100.)/100.;

floating point for more details.

Left Zeros

public static String toLZ( int i, int len )
   {
   // converts integer to left-zero padded string, len  chars long.
   String s = Integer.toString(i);
   if ( s.length() > len ) return s.substring(0,len);
   else if ( s.length() < len ) // pad on left with zeros
      return "000000000000000000000000000".substring(0, len - s.length ()) + s;
   else return s;
   } // end toLZ

Formatted Output

JDK 1.1+ has formatting picture classes such as java.util.DateFormat, SimpleDateFormat and DecimalFormat.

Formatting is such a common request, you might attain sainthood if you wrote a formatting class that gives you all the power of printf without the overhead of parsing strings for % produce a string. e.g.

Java 1.5+, java.io. PrintWriter. printf, java.io. PrintStream. printf and the java.util. Formatter class give you abilities similar to C’s printf. See printf for more details.

Reading Numeric Data From an ASCII file

You have to roll your own method. You may be able to use my CSVReader class. Or use java.io.StreamTokenizer or java.util.StringTokenizer, perhaps in combination with readLine to get your data into strings. StreamTokenizer has bells and whistles to deal with parsing source code, including white space, comments and numbers. StringTokenizer just splits the text up based on delimiter characters. Then use the conversion methods in the table above to convert to integers etc. See below for a simplified examples of how you would do this.

StreamTokenizer Method of Reading Integers From An ASCII File

StringTokenizer Method of Reading Integers From An ASCII file

Binary

Metric Conversions

Learning More