java j2ee interview questions: GWT NumberFormat Example

public class NumberFormat
extends java.lang.Object
extends java.lang.Object

Formats and parses numbers using locale-sensitive patterns.

This class provides comprehensive and flexible support for a wide variety of
localized formats, including

Locale-specific symbols such as decimal point, group separator,
digit representation, currency symbol, percent, and permill

Numeric variations including integers ("123"), fixed-point
numbers ("123.4"), scientific notation ("1.23E4"), percentages ("12%"), and
currency amounts ("$123")

Predefined standard patterns that can be used both for parsing
and formatting, including decimal,
currency,
percentages, and
scientific

Custom patterns and supporting features designed to make it
possible to parse and format numbers in any locale, including support for
Western, Arabic, and Indic digits

Patterns

Formatting and parsing are based on customizable patterns that can include a
combination of literal characters and special characters that act as
placeholders and are replaced by their localized counterparts. Many
characters in a pattern are taken literally; they are matched during parsing
and output unchanged during formatting. Special characters, on the other
hand, stand for other characters, strings, or classes of characters. For
example, the '#' character is replaced by a localized digit.

Often the replacement character is the same as the pattern character. In the
U.S. locale, for example, the ',' grouping character is
replaced by the same character ','. However, the replacement
is still actually happening, and in a different locale, the grouping
character may change to a different character, such as '.'.
Some special characters affect the behavior of the formatter by their
presence. For example, if the percent character is seen, then the value is
multiplied by 100 before being displayed.

The characters listed below are used in patterns. Localized symbols use the
corresponding characters taken from corresponding locale symbol collection,
which can be found in the properties files residing in the
com.google.gwt.i18n.client.constants. To insert
a special character in a pattern as a literal (that is, without any special
meaning) the character must be quoted. There are some exceptions to this
which are noted below.

A NumberFormat pattern contains a postive and negative
subpattern separated by a semicolon, such as
"#,##0.00;(#,##0.00)". Each subpattern has a prefix, a
numeric part, and a suffix. If there is no explicit negative subpattern, the
negative subpattern is the localized minus sign prefixed to the positive
subpattern. That is, "0.00" alone is equivalent to
"0.00;-0.00". If there is an explicit negative subpattern, it
serves only to specify the negative prefix and suffix; the number of digits,
minimal digits, and other characteristics are ignored in the negative
subpattern. That means that "#,##0.0#;(#)" has precisely the
same result as "#,##0.0#;(#,##0.0#)".

The prefixes, suffixes, and various symbols used for infinity, digits,
thousands separators, decimal separators, etc. may be set to arbitrary
values, and they will appear properly during formatting. However, care must
be taken that the symbols and strings do not conflict, or parsing will be
unreliable. For example, the decimal separator and thousands separator should
be distinct characters, or parsing will be impossible.

The grouping separator is a character that separates clusters of integer
digits to make large numbers more legible. It commonly used for thousands,
but in some locales it separates ten-thousands. The grouping size is the
number of digits between the grouping separators, such as 3 for "100,000,000"
or 4 for "1 0000 0000".

Pattern Grammar (BNF)

The pattern itself uses the following grammar:

pattern:=subpattern (';' subpattern)?
subpattern:=prefix? number exponent? suffix?
number:=(integer ('.' fraction)?) sigDigits
prefix:='\u0000'..'\uFFFD' - specialCharacters
suffix:='\u0000'..'\uFFFD' - specialCharacters
integer:='#'* '0'*'0'
fraction:='0'* '#'*
sigDigits:='#'* '@''@'* '#'*
exponent:='E' '+'? '0'* '0'
padSpec:='*' padChar
padChar:='\u0000'..'\uFFFD' - quote

Notation:

X* 0 or more instances of X
X? 0 or 1 instances of X
XY either X or Y
C..D any character from C up to D, inclusive
S-T characters in S, except those in T

The first subpattern is for positive numbers. The second (optional) subpattern is for negative numbers.

Example

public class NumberFormatExample implements EntryPoint {

  public void onModuleLoad() {
    NumberFormat fmt = NumberFormat.getDecimalFormat();
    double value = 12345.6789;
    String formatted = fmt.format(value);
    // Prints 1,2345.6789 in the default locale
    GWT.log("Formatted string is" + formatted, null);

    // Turn a string back into a double
    value = NumberFormat.getDecimalFormat().parse("12345.6789");
    GWT.log("Parsed value is" + value, null);

    // Scientific notation
    value = 12345.6789;
    formatted = NumberFormat.getScientificFormat().format(value);
    // prints 1.2345E4 in the default locale
    GWT.log("Formatted string is" + formatted, null);

    // Currency
    fmt = NumberFormat.getCurrencyFormat();
    formatted = fmt.format(123456.7899);
    // prints $123,456.79 in the default locale
    GWT.log("Formatted currency is" + formatted, null);

    // Custom format
    value = 12345.6789;
    formatted = NumberFormat.getFormat("000000.000000").format(value);
    // prints 012345.678900 in the default locale
    GWT.log("Formatted string is" + formatted, null);
  }
}

Constructor Detail

NumberFormat


protected NumberFormat(com.google.gwt.i18n.client.constants.NumberConstants numberConstants,
                       java.lang.String pattern,
                       com.google.gwt.i18n.client.impl.CurrencyData cdata,
                       boolean userSuppliedPattern)

Constructs a format object based on the specified settings.

NumberFormat

protected NumberFormat(java.lang.String pattern,
                       com.google.gwt.i18n.client.impl.CurrencyData cdata,
                       boolean userSuppliedPattern)

Constructs a format object for the default locale based on the specified
settings.

Method Detail

getCurrencyFormat


public static NumberFormat getCurrencyFormat()

Provides the standard currency format for the default locale.

getCurrencyFormat
public static NumberFormat getCurrencyFormat(java.lang.String currencyCode)

Provides the standard currency format for the default locale using a
specified currency.

getDecimalFormat


public static NumberFormat getDecimalFormat()

Provides the standard decimal format for the default locale.

Returns:

a NumberFormat capable of producing and consuming
decimal format for the default locale

getFormat
public static NumberFormat getFormat(java.lang.String pattern)

Gets a NumberFormat instance for the default locale using
the specified pattern and the default currencyCode.

Parameters:: pattern - pattern for this formatter
Returns:: a NumberFormat instance
Throws:: java.lang.IllegalArgumentException - if the specified pattern is invalid

getFormat

public static NumberFormat getFormat(java.lang.String pattern,
                                     java.lang.String currencyCode)

Gets a custom NumberFormat instance for the default locale
using the specified pattern and currency code.

getPercentFormat


public static NumberFormat getPercentFormat()

Provides the standard percent format for the default locale.

Returns:

a NumberFormat capable of producing and consuming
percent format for the default locale

getScientificFormat


public static NumberFormat getScientificFormat()

Provides the standard scientific format for the default locale.

Returns:

a NumberFormat capable of producing and consuming
scientific format for the default locale

format


public java.lang.String format(double number)

This method formats a double to produce a string.
Parameters:

getPattern
public java.lang.String getPattern()

Returns the pattern used by this number format.

parse
public double parse(java.lang.String text)

throws java.lang.NumberFormatException

Parses text to produce a numeric value. A NumberFormatException is
thrown if either the text is empty or if the parse does not consume all
characters of the text.

parse
public double parse(java.lang.String text,

int[] inOutPos)

throws java.lang.NumberFormatException

Parses text to produce a numeric value.

The method attempts to parse text starting at the index given by pos. If
parsing succeeds, then the index of pos is updated to the
index after the last character used (parsing does not necessarily use all
characters up to the end of the string), and the parsed number is returned.
The updated pos can be used to indicate the starting point
for the next call to this method. If an error occurs, then the index of
pos is not changed.

java j2ee interview questions

Tuesday, June 23, 2009

GWT NumberFormat Example

Patterns

Pattern Grammar (BNF)

Example

NumberFormat

NumberFormat

getCurrencyFormat

getFormat

getScientificFormat

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