Detailed description of DecimalFormat rounding in java,

Detailed description of DecimalFormat rounding in java,

DecimalFormat is a subclass of NumberFormat used to format decimal numbers. It supports different types of numbers, including INTEGER (123), fixed point (123.4), Scientific notation (1.23E4), percentage (12%), and amount ($123) the content is localized.

The following describes the usage of DecimalFormat:

Import java. text. *; import java. util. *; public class DecimalFormatDemo {public static void main (String args []) {DecimalFormat df1 = new DecimalFormat ("###,###. 0000 "); // use the default System format. out. println (df1.format (111111123456.12); Locale. setDefault (Locale. US); DecimalFormat df2 = new DecimalFormat ("###,###. 0000 "); // use the US format System. out. println (df2.format (111111123456.12); // ---------------------------- also use applypattern values // DecimalFormat df3 = new DecimalFormat (); myformat3.applyPattern ("##,###. 000 "); System. out. println (df3.format (11112345.12345); // ----------------- control index output; // DecimalFormat df4 = new DecimalFormat (); myformat4.applyPattern ("0.000E0000"); System. out. println (df4.format (10000); System. out. println (df4.format (12345678.345); // -------------------- percentage output --------------------------------------------- // DecimalFormat df5 = null; try {df5 = (DecimalFormat) NumberFormat. getPercentInstance ();} catch (ClassCastException e) {<span style = "white-space: pre"> </span> System. err. println (e);} df5.applyPattern ("00.0000%"); System. out. println (df5.format (0.34567); System. out. println (df5.format (1.34567 ));}}

(1) Rounding data:

DecimalFormat contains a group of symbols. The meanings of these symbols are described as follows:

0: a number

# A number, excluding 0

. Placeholder for decimal separator

, Group separator placeholder

; Separator format.

-Default negative prefix.

% Multiplied by 100 and displayed as Percentage

? Multiply by 1000 and display it as a kilobytes of currency; replace it with a currency symbol; replace it with an international currency symbol if you double write. If it appears in a mode, the decimal separator is used as the decimal separator.

Any other character used in the X prefix or suffix to reference special characters in the prefix or suffix.

For example:

DecimalFormat df1 = new DecimalFormat ("### 0.00"); // retain two decimal places. If less than two decimal places exist, the System is automatically set to zero. out. println (df1.format (124.367); System. out. println (df1.format (124.3); DecimalFormat df2 = new DecimalFormat ("### 0. # "); // retain two decimal places. If there are less than two decimal places, the System is not supplemented. out. println (df2.format (124.6); System. out. println (df2.format (124); DecimalFormat df3 = new DecimalFormat ("000.000"); // retain three decimal places. If the number is not enough, add System. out. println (df3.format (24); DecimalFormat df = new DecimalFormat ("0.000E0000"); // index System. out. println (df. format (1234.56); DecimalFormat nf = (DecimalFormat) NumberFormat. getPercentInstance (); // percentage System. out. println (nf. format (0.476354); nf. applyPattern ("00.00%"); System. out. println (nf. formats (0.476354 ));

Running result:

124.37 124.30 124.6 124 024.000 1.235E0003 48% 47.64% 

(2) For reading and parsing strings containing formatted numbers? Resolution can be included in NumberFormat. For example:

Import java. util. locale; import java. text. numberFormat; import java. text. parseException; public class DecimalFormat5 {public static void main (String args []) {// local format NumberFormat nf1 = NumberFormat. getInstance (); Object obj1 = null; // format-based parsing try {obj1 = nf1.parse ("1234,56");} catch (ParseException e1) {System. err. println (e1);} System. out. println (obj1); // German format NumberFormat nf2 = NumberFormat. getInstance (Locale. GERMAN); Object obj2 = null; // format-based parsing try {obj2 = nf2.parse ("1234,56");} catch (ParseException e2) {System. err. println (e2);} System. out. println (obj2 );}}

Running result:

123456 // run in the United States; considered string 1234.56 // run in Germany; Considered as a decimal

(3) For DecimalFormat and NumberFormat:

DecimalFormat is a subclass of NumberFormat. Its instance is specified as a specific region. Therefore, you can use NumberFormat. getInstance to specify a region and forcibly convert the structure to a DecimalFormat object. This technology can be applied in most cases, however, you need to use try/catch Block to enclose the forced conversion to prevent the conversion from working properly (probably using a strange region in a very unknown situation ).

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