java的NumberFormat、DecimalFormat、MessageFormat类源码详解
NumberFormat类的定义
public abstract class NumberFormat extends Format {
protected NumberFormat() {
}
@Override
public StringBuffer format(Object number,
StringBuffer toAppendTo,
FieldPosition pos) {
if (number instanceof Long || number instanceof Integer ||
number instanceof Short || number instanceof Byte ||
number instanceof AtomicInteger || number instanceof AtomicLong ||
(number instanceof BigInteger &&
((BigInteger)number).bitLength() < 64)) {
return format(((Number)number).longValue(), toAppendTo, pos);
} else if (number instanceof Number) {
return format(((Number)number).doubleValue(), toAppendTo, pos);
} else {
throw new IllegalArgumentException("Cannot format given Object as a Number");
}
}
@Override
public final Object parseObject(String source, ParsePosition pos) {
return parse(source, pos);
}
public final String format(double number) {
// Use fast-path for double result if that works
String result = fastFormat(number);
if (result != null)
return result;
return format(number, new StringBuffer(),
DontCareFieldPosition.INSTANCE).toString();
}
String fastFormat(double number) { return null; }
public final String format(long number) {
return format(number, new StringBuffer(),
DontCareFieldPosition.INSTANCE).toString();
}
public abstract StringBuffer format(double number,
StringBuffer toAppendTo,
FieldPosition pos);
public abstract StringBuffer format(long number,
StringBuffer toAppendTo,
FieldPosition pos);
public abstract Number parse(String source, ParsePosition parsePosition);
public Number parse(String source) throws ParseException {
ParsePosition parsePosition = new ParsePosition(0);
Number result = parse(source, parsePosition);
if (parsePosition.index == 0) {
throw new ParseException("Unparseable number: \"" + source + "\"",
parsePosition.errorIndex);
}
return result;
}
public boolean isParseIntegerOnly() {
return parseIntegerOnly;
}
public void setParseIntegerOnly(boolean value) {
parseIntegerOnly = value;
}
//============== Locale Stuff =====================
public final static NumberFormat getInstance() {
return getInstance(Locale.getDefault(Locale.Category.FORMAT), NUMBERSTYLE);
}
public static NumberFormat getInstance(Locale inLocale) {
return getInstance(inLocale, NUMBERSTYLE);
}
public final static NumberFormat getNumberInstance() {
return getInstance(Locale.getDefault(Locale.Category.FORMAT), NUMBERSTYLE);
}
public static NumberFormat getNumberInstance(Locale inLocale) {
return getInstance(inLocale, NUMBERSTYLE);
}
public final static NumberFormat getIntegerInstance() {
return getInstance(Locale.getDefault(Locale.Category.FORMAT), INTEGERSTYLE);
}
public static NumberFormat getIntegerInstance(Locale inLocale) {
return getInstance(inLocale, INTEGERSTYLE);
}
public final static NumberFormat getCurrencyInstance() {
return getInstance(Locale.getDefault(Locale.Category.FORMAT), CURRENCYSTYLE);
}
public static NumberFormat getCurrencyInstance(Locale inLocale) {
return getInstance(inLocale, CURRENCYSTYLE);
}
public final static NumberFormat getPercentInstance() {
return getInstance(Locale.getDefault(Locale.Category.FORMAT), PERCENTSTYLE);
}
public static NumberFormat getPercentInstance(Locale inLocale) {
return getInstance(inLocale, PERCENTSTYLE);
}
/*public*/ final static NumberFormat getScientificInstance() {
return getInstance(Locale.getDefault(Locale.Category.FORMAT), SCIENTIFICSTYLE);
}
/*public*/ static NumberFormat getScientificInstance(Locale inLocale) {
return getInstance(inLocale, SCIENTIFICSTYLE);
}
public static Locale[] getAvailableLocales() {
LocaleServiceProviderPool pool =
LocaleServiceProviderPool.getPool(NumberFormatProvider.class);
return pool.getAvailableLocales();
}
@Override
public int hashCode() {
return maximumIntegerDigits * 37 + maxFractionDigits;
// just enough fields for a reasonable distribution
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (this == obj) {
return true;
}
if (getClass() != obj.getClass()) {
return false;
}
NumberFormat other = (NumberFormat) obj;
return (maximumIntegerDigits == other.maximumIntegerDigits
&& minimumIntegerDigits == other.minimumIntegerDigits
&& maximumFractionDigits == other.maximumFractionDigits
&& minimumFractionDigits == other.minimumFractionDigits
&& groupingUsed == other.groupingUsed
&& parseIntegerOnly == other.parseIntegerOnly);
}
@Override
public Object clone() {
NumberFormat other = (NumberFormat) super.clone();
return other;
}
}
import java.text.* ;
public class NumberFormatDemo01{
public static void main(String args[]){
NumberFormat nf = null ; // 声明一个NumberFormat对象
nf = NumberFormat.getInstance() ; // 得到默认的数字格式化显示
System.out.println("格式化之后的数字：" + nf.format(10000000)) ;
System.out.println("格式化之后的数字：" + nf.format(1000.345)) ;
}
}; import java.text.NumberFormat;
1。Decimalformat df1 = new Decimalformat("####.000");
System.out.println(df1.format(1234.56));
显示：1234.560
2。NumberFormat nf = NumberFormat.getPercentInstance();
// nf.setMinimumFractionDigits( 2 ); 保留到小数点后几位 显示：47.00%
System.out.println(nf.format(0.47));
显示：47%
(法二)
DecimalFormat df1 = new DecimalFormat("##.00%"); //##.00% 百分比格式，后面不足2位的用0补齐
baifenbi= df1.format(fen);
显示：47.00%
扫描二维码关注公众号，回复：
10470159 查看本文章
3。DecimalFormat df = new DecimalFormat("###,##0.00");
System.out.println(nf.format(24.7));
显示：24.70
System.out.println(nf.format(23123.47));
显示：123,23.47
补充：0.00、0.01; 0.00%、0.12%这样的数据，如果按照上面的格式可能会造成数据显示成：.00、.01; .00%、.12%，怎么办呢？只要把格式改成：
DecimalFormat df1 = new DecimalFormat("0.00");
DecimalFormat df2 = new DecimalFormat("0.00%");
df1.formatI（number）;df2.formatI（number）;
显示：0.00、0.01; 0.00%、0.12%
public class Test {
public static void main(String[] args) {
Double myNumber=23323.3323232323;
Double test=0.3434;
//getInstance()
//返回当前缺省语言环境的缺省数值格式。
String myString = NumberFormat.getInstance().format(myNumber);
System.out.println(myString);
//getCurrencyInstance()返回当前缺省语言环境的通用格式
myString = NumberFormat.getCurrencyInstance().format(myNumber);
System.out.println(myString);
//getNumberInstance() 返回当前缺省语言环境的通用数值格式。
myString = NumberFormat.getNumberInstance().format(myNumber);
System.out.println(myString);
//getPercentInstance() 返回当前缺省语言环境的百分比格式。
myString = NumberFormat.getPercentInstance().format(test);
System.out.println(myString);
//setMaximumFractionDigits(int) 设置数值的小数部分允许的最大位数。
//setMaximumIntegerDigits(int) 设置数值的整数部分允许的最大位数。
//setMinimumFractionDigits(int) 设置数值的小数部分允许的最小位数。
//setMinimumIntegerDigits(int) 设置数值的整数部分允许的最小位数.
NumberFormat format = NumberFormat.getInstance();
format.setMinimumFractionDigits( 3 );
format.setMaximumFractionDigits(5);
format.setMaximumIntegerDigits( 10 );
format.setMinimumIntegerDigits(0);
System.out.println(format.format(2132323213.23266666666));
}
}结果为:
23,323.332
￥23,323.33
23,323.332
34%
2,132,323,213.23267
MessageFormat
public class MessageFormat extends Format {
private static final long serialVersionUID = 6479157306784022952L;
public MessageFormat(String pattern) {
this.locale = Locale.getDefault(Locale.Category.FORMAT);
applyPattern(pattern);
}
public MessageFormat(String pattern, Locale locale) {
this.locale = locale;
applyPattern(pattern);
}
public void setLocale(Locale locale) {
this.locale = locale;
}
public Locale getLocale() {
return locale;
}
@SuppressWarnings("fallthrough") // fallthrough in switch is expected, suppress it
public void applyPattern(String pattern) {
StringBuilder[] segments = new StringBuilder[4];
// Allocate only segments[SEG_RAW] here. The rest are
// allocated on demand.
segments[SEG_RAW] = new StringBuilder();
int part = SEG_RAW;
int formatNumber = 0;
boolean inQuote = false;
int braceStack = 0;
maxOffset = -1;
for (int i = 0; i < pattern.length(); ++i) {
char ch = pattern.charAt(i);
if (part == SEG_RAW) {
if (ch == '\'') {
if (i + 1 < pattern.length()
&& pattern.charAt(i+1) == '\'') {
segments[part].append(ch); // handle doubles
++i;
} else {
inQuote = !inQuote;
}
} else if (ch == '{' && !inQuote) {
part = SEG_INDEX;
if (segments[SEG_INDEX] == null) {
segments[SEG_INDEX] = new StringBuilder();
}
} else {
segments[part].append(ch);
}
} else {
if (inQuote) { // just copy quotes in parts
segments[part].append(ch);
if (ch == '\'') {
inQuote = false;
}
} else {
switch (ch) {
case ',':
if (part < SEG_MODIFIER) {
if (segments[++part] == null) {
segments[part] = new StringBuilder();
}
} else {
segments[part].append(ch);
}
break;
case '{':
++braceStack;
segments[part].append(ch);
break;
case '}':
if (braceStack == 0) {
part = SEG_RAW;
makeFormat(i, formatNumber, segments);
formatNumber++;
// throw away other segments
segments[SEG_INDEX] = null;
segments[SEG_TYPE] = null;
segments[SEG_MODIFIER] = null;
} else {
--braceStack;
segments[part].append(ch);
}
break;
case ' ':
// Skip any leading space chars for SEG_TYPE.
if (part != SEG_TYPE || segments[SEG_TYPE].length() > 0) {
segments[part].append(ch);
}
break;
case '\'':
inQuote = true;
// fall through, so we keep quotes in other parts
default:
segments[part].append(ch);
break;
}
}
}
}
if (braceStack == 0 && part != 0) {
maxOffset = -1;
throw new IllegalArgumentException("Unmatched braces in the pattern.");
}
this.pattern = segments[0].toString();
}
public String toPattern() {
// later, make this more extensible
int lastOffset = 0;
StringBuilder result = new StringBuilder();
for (int i = 0; i <= maxOffset; ++i) {
copyAndFixQuotes(pattern, lastOffset, offsets[i], result);
lastOffset = offsets[i];
result.append('{').append(argumentNumbers[i]);
Format fmt = formats[i];
if (fmt == null) {
// do nothing, string format
} else if (fmt instanceof NumberFormat) {
if (fmt.equals(NumberFormat.getInstance(locale))) {
result.append(",number");
} else if (fmt.equals(NumberFormat.getCurrencyInstance(locale))) {
result.append(",number,currency");
} else if (fmt.equals(NumberFormat.getPercentInstance(locale))) {
result.append(",number,percent");
} else if (fmt.equals(NumberFormat.getIntegerInstance(locale))) {
result.append(",number,integer");
} else {
if (fmt instanceof DecimalFormat) {
result.append(",number,").append(((DecimalFormat)fmt).toPattern());
} else if (fmt instanceof ChoiceFormat) {
result.append(",choice,").append(((ChoiceFormat)fmt).toPattern());
} else {
// UNKNOWN
}
}
} else if (fmt instanceof DateFormat) {
int index;
for (index = MODIFIER_DEFAULT; index < DATE_TIME_MODIFIERS.length; index++) {
DateFormat df = DateFormat.getDateInstance(DATE_TIME_MODIFIERS[index],
locale);
if (fmt.equals(df)) {
result.append(",date");
break;
}
df = DateFormat.getTimeInstance(DATE_TIME_MODIFIERS[index],
locale);
if (fmt.equals(df)) {
result.append(",time");
break;
}
}
if (index >= DATE_TIME_MODIFIERS.length) {
if (fmt instanceof SimpleDateFormat) {
result.append(",date,").append(((SimpleDateFormat)fmt).toPattern());
} else {
// UNKNOWN
}
} else if (index != MODIFIER_DEFAULT) {
result.append(',').append(DATE_TIME_MODIFIER_KEYWORDS[index]);
}
} else {
//result.append(", unknown");
}
result.append('}');
}
copyAndFixQuotes(pattern, lastOffset, pattern.length(), result);
return result.toString();
}
public final StringBuffer format(Object[] arguments, StringBuffer result,
FieldPosition pos)
{
return subformat(arguments, result, pos, null);
}
public static String format(String pattern, Object ... arguments) {
MessageFormat temp = new MessageFormat(pattern);
return temp.format(arguments);
}
// Overrides
public final StringBuffer format(Object arguments, StringBuffer result,
FieldPosition pos)
{
return subformat((Object[]) arguments, result, pos, null);
}
public Object[] parse(String source, ParsePosition pos) {
if (source == null) {
Object[] empty = {};
return empty;
}
int maximumArgumentNumber = -1;
for (int i = 0; i <= maxOffset; i++) {
if (argumentNumbers[i] > maximumArgumentNumber) {
maximumArgumentNumber = argumentNumbers[i];
}
}
Object[] resultArray = new Object[maximumArgumentNumber + 1];
int patternOffset = 0;
int sourceOffset = pos.index;
ParsePosition tempStatus = new ParsePosition(0);
for (int i = 0; i <= maxOffset; ++i) {
// match up to format
int len = offsets[i] - patternOffset;
if (len == 0 || pattern.regionMatches(patternOffset,
source, sourceOffset, len)) {
sourceOffset += len;
patternOffset += len;
} else {
pos.errorIndex = sourceOffset;
return null; // leave index as is to signal error
}
// now use format
if (formats[i] == null) { // string format
// if at end, use longest possible match
// otherwise uses first match to intervening string
// does NOT recursively try all possibilities
int tempLength = (i != maxOffset) ? offsets[i+1] : pattern.length();
int next;
if (patternOffset >= tempLength) {
next = source.length();
}else{
next = source.indexOf(pattern.substring(patternOffset, tempLength),
sourceOffset);
}
if (next < 0) {
pos.errorIndex = sourceOffset;
return null; // leave index as is to signal error
} else {
String strValue= source.substring(sourceOffset,next);
if (!strValue.equals("{"+argumentNumbers[i]+"}"))
resultArray[argumentNumbers[i]]
= source.substring(sourceOffset,next);
sourceOffset = next;
}
} else {
tempStatus.index = sourceOffset;
resultArray[argumentNumbers[i]]
= formats[i].parseObject(source,tempStatus);
if (tempStatus.index == sourceOffset) {
pos.errorIndex = sourceOffset;
return null; // leave index as is to signal error
}
sourceOffset = tempStatus.index; // update
}
}
int len = pattern.length() - patternOffset;
if (len == 0 || pattern.regionMatches(patternOffset,
source, sourceOffset, len)) {
pos.index = sourceOffset + len;
} else {
pos.errorIndex = sourceOffset;
return null; // leave index as is to signal error
}
return resultArray;
}
public Object[] parse(String source) throws ParseException {
ParsePosition pos = new ParsePosition(0);
Object[] result = parse(source, pos);
if (pos.index == 0) // unchanged, returned object is null
throw new ParseException("MessageFormat parse error!", pos.errorIndex);
return result;
}
public Object parseObject(String source, ParsePosition pos) {
return parse(source, pos);
}
public Object clone() {
MessageFormat other = (MessageFormat) super.clone();
// clone arrays. Can't do with utility because of bug in Cloneable
other.formats = formats.clone(); // shallow clone
for (int i = 0; i < formats.length; ++i) {
if (formats[i] != null)
other.formats[i] = (Format)formats[i].clone();
}
// for primitives or immutables, shallow clone is enough
other.offsets = offsets.clone();
other.argumentNumbers = argumentNumbers.clone();
return other;
}
public boolean equals(Object obj) {
if (this == obj) // quick check
return true;
if (obj == null || getClass() != obj.getClass())
return false;
MessageFormat other = (MessageFormat) obj;
return (maxOffset == other.maxOffset
&& pattern.equals(other.pattern)
&& ((locale != null && locale.equals(other.locale))
|| (locale == null && other.locale == null))
&& Arrays.equals(offsets,other.offsets)
&& Arrays.equals(argumentNumbers,other.argumentNumbers)
&& Arrays.equals(formats,other.formats));
}
public static class Field extends Format.Field {
// Proclaim serial compatibility with 1.4 FCS
private static final long serialVersionUID = 7899943957617360810L;
protected Field(String name) {
super(name);
}
protected Object readResolve() throws InvalidObjectException {
if (this.getClass() != MessageFormat.Field.class) {
throw new InvalidObjectException("subclass didn't correctly implement readResolve");
}
return ARGUMENT;
}
//
// The constants
//
public final static Field ARGUMENT =
new Field("message argument field");
}
}为什么要使用静态内部类
class Company {
private String theCEO = "stupid";
private static String companyName = "STUPID COM";
// 1
static class Employee {
public Employee() {
System.out.println("company name - " + companyName);
// 2
//System.out.println("CEO - " + theCEO);
}
}
public Company(){
System.out.println("Company object is created");
}
}
public class Main {
public static void main(String[] args) {
// Company company = new Company();
// Company.Employee employee = company.new Employee();
// 3
Company.Employee employee = new Company.Employee();
}
}
如果内部类不是静态的。要用这个内部类就必须先初始化包裹类。也是，如果不初始化出来对应的包裹类，内部类对象怎么能访问这些包裹类对象的非静态实例对象呢。
- 加
static，员工类变成静态内部类。 - 静态内部类不能再访问包裹类的非静态成员。
- 看起来正常的初始化方法：
new Company.Employee()。
一般来说，内部类不需要访问包裹类的非静态成员的时候。或者只是做一个工具给外部调用，而这些工具需要按照功能区分为的时候使用静态内部类。
FormatElement:
{ ArgumentIndex }
{ ArgumentIndex , FormatType }
{ ArgumentIndex , FormatType , FormatStyle }
FormatType:
number
date
time
choice(需要使用ChoiceFormat)
FormatStyle:
short
medium
long
full
integer
currency
percent
SubformatPattern(子模式)
{0}、{1,number,short}、{2,number,#.#}属于FormatElement，0,1,2是ArgumentIndex
{1,number,short}里面的number属于FormatType，short则属于FormatStyle
{1,number,#.#}里面的#.#就属于子格式模式
import java.text.MessageFormat;
String str = "{0}{1}{2}{3}{4}{5}{6}{7}{8}{9}{10}{11}{12}{13}{14}{15}{16}";
Object[] array = new Object[]{"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q"};
String value = MessageFormat.format(str, array);
System.out.println(value); // ABCDEFGHIJKLMNOPQ
String message = "oh, {0} is a person";
Object[] array = new Object[]{"ZhangSan"};
String value = MessageFormat.format(message, array);
System.out.println(value); // oh, ZhangSan is a person
String message = "oh, {0,number,#.#} is a number";
Object[] array = new Object[]{new Double(3.1415)};
String value = MessageFormat.format(message, array);
System.out.println(value); // oh, 3.1 is a number
// MessageFormat的format方法源码
public static String format(String pattern, Object ... arguments)
{
MessageFormat temp = new MessageFormat(pattern);
return temp.format(arguments);
}对字符串的匹配比较智能
String str = "{0} | {1} | {0} | {1}";
Object[] array = new Object[] { "A", "B" };
String value = MessageFormat.format(str, array);
System.out.println(value); // A | B | A | B StringBuilder sb=new StringBuilder();
sb.append(" insert into test_tb (");
sb.append(" createTime, ");
sb.append(" datefrom, ");
sb.append(" dateto, ");
sb.append(" name, ");
sb.append(" intranetid, ");
sb.append(" actualhour, ");
sb.append(" planhour, ");
sb.append(" status");
sb.append(" ) values (");
sb.append(" ''{0}'',");
sb.append(" ''{1}'',");
sb.append(" ''{2}'',");
sb.append(" ''{3}'',");
sb.append(" ''{4}'',");
sb.append(" ''{5}'',");
sb.append(" ''{6}'',");
sb.append(" ''{7}''");
sb.append(" )");
String result=sb.toString();
Object[] arr={createTime,datefrom,dateto,name,intranetid,actualhour,planhour,status};
String sql=MessageFormat.format(result, arr);