Java conversions

Last updated Thursday, 28-Jan-1999 03:24:20 PDT by Roedy Green ©1997-1999 Canadian Mind Products.

This table will help you convert from any of the basic data types to any other. Please report any errors or omissions. This table is also available as an amanunesis Applet or as a download with source code.

I find the lack of symmetry in this table most distressing. The namings remind me of the art of venery practiced in the middle ages as a sort of one-up-manship. It is probably too late now to hope for these conversion names to be rationalised. Perhaps someone will invent a preprocessor so that you can use a simple (xxx)-style cast to convert from anything to anything.

Hexadecimal

The radix feature of the toString and parseInt methods lets you handle hexadecimal numbers. Just set the radix to 16.

StringBuffers

Strings and StringBuffers can be interconverted.

StringBuffer q;
String s;

q = new StringBuffer(s);

s = new String(q);
s = q.toString();

Rounding

Rounding often surprises because fractions like 0.1 cannot be precisely be represented in IEEE floating point format. Often you find yourself having to add tiny numbers just prior to printing to get the desired effects.

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.;

Left Zeros

The standard conversions give you no leading blanks or leading zeroes. Here is a code snippet to convert an integer to string padded with leading left zeroes. With an obvious modification it would give you lead blanks.

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 1.0.2 has no function like C's printf that lets you control how many positions and decimal places you want in your output. You have to roll your own.

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

Formatting for 1.0.2 is such a common request, you might attain sainthood if you either implemented the 1.1 methods or wrote a formatting class that gives you all the power of printf without the overhead of parsing strings for % produce a string. e.g.

class Form {
static String display(int value, int width, int decimalPlaces, int base, boolean leadZeroes);
static String display(int value, int width, int decimalPlaces, int base);
static String display(int value, int width, int decimalPlaces);
static String display(int value, int width);
static String display(int value);
static String display(double value, int width, int decimalPlaces);
static String display(double value, int width);
static String display(double value);
... };

Acme has written a class to do formatting. They provide source.

Reading Numeric Data From an ASCII file

Java has no built-in methods for reading data of the form: 123 456,-4.

You have to roll your own method. 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

// Read space or comma-delimited file of integers
// Convert from ASCII to internal binary

import java.io.*;
import java.io.StreamTokenizer;

...

// In JDK 1.1
BufferedReader in =
    new BufferedReader(new FileReader("C:\\temp\\foo.in"));

// in JDK 1.0.2
BufferedInputStream in =
    new BufferedInputStream(new FileInputStream("C:\\temp\\foo.in"));

StreamTokenizer st = new StreamTokenizer(in);
    // process the entire file, of space or comma-delimited ints
    int found = StreamTokenizer.TT_NUMBER;
    while (found != StreamTokenizer.TT_EOF) {
        found = st.nextToken();
        if (found == StreamTokenizer.TT_NUMBER) {
            int i = (int) st.nval;
            System.out.println(i);
            } // end if
    } // end while

StringTokenizer Method Of Reading Integers From An ASCII file

// Read space-delimited file of integers
// Convert from ASCII to internal binary

import java.io.*;
import java.util.StringTokenizer;

...

DataInputStream in = new DataInputStream(
    new BufferedInputStream(new FileInputStream("C:\\temp\\foo.in")));
String aLine = in.readLine();
StringTokenizer st = new StringTokenizer(aLine);
    // process one line worth of space-delimited integers
    while (st.hasMoreTokens()) {
        String s = st.nextToken();
        int i = Integer.parseInt(s);
        System.out.println(i);
        } // end while

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