long g = (long)9223372036854775807;
long h = (long)-9223372036854775808;



long g = 9223372036854775807;
long h = -9223372036854775808;

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
The literal 9223372036854775807 of type int is out of range
The literal 9223372036854775808 of type int is out of range 

~

L

long value = 9223372036854775807L;

short a = 1;
short b = 2;

a+b

javaintjavaintint

1

floatdouble

float f1=100.00f;
Float F1=new Float(f1);
double d1=F1.doubleValue();//F1.doubleValue()Floatdouble

Boolean(boolean value)Character(char value)Integer(int value)Long(long value)Float(float value)Double(double value)

Value()intValue()doubleValue()

2

• :X.toString();
• :X+"";
• String:String.valueOf(X);

3,

1,

"32.1"double:new Float("32.1").doubleValue():Double.valueOf("32.1").doubleValue()

2parseXXX

String s = "1";
byte b = Byte.parseByte( s );
short t = Short.parseShort( s );
int i = Integer.parseInt( s );
long l = Long.parseLong( s );
Float f = Float.parseFloat( s );
Double d = Double.parseDouble( s );

3CharactergetNumericValue(char ch)

4Date

DateintDate

• Date(int year, int month, int date)int
• Date(int year, int month, int date, int hrs, int min)int
• Date(int year, int month, int date, int hrs, int min, int sec)int

Date197011000DateDate(long date)

DateDategetYear()getMonth()getDate()getHours()getMinutes()getSeconds()getDay()Dateint

DategetTime()DatetoString()String

Date20020324

import java.text.SimpleDateFormat;

java.util.Date date = new java.util.Date();
//YYYYMMDD
SimpleDateFormat sy1=new SimpleDateFormat("yyyyMMdd");
String dateFormat=sy1.format(date);
//
SimpleDateFormat sy=new SimpleDateFormat("yyyy");
SimpleDateFormat sm=new SimpleDateFormat("MM");
SimpleDateFormat sd=new SimpleDateFormat("dd");
String syear=sy.format(date);
String smon=sm.format(date);
String sday=sd.format(date);

1 boolean

2

• a.
• b.
• float intfloat longdouble intdouble long
• c.
• d.

3

Integer

Integer a = 1;

int Integer Integer valueOf(int i)

Integer a = Integer.valueOf(1);

/**
 * Returns an {@code Integer} instance representing the specified
 * {@code int} value.  If a new {@code Integer} instance is not
 * required, this method should generally be used in preference to
 * the constructor {@link #Integer(int)}, as this method is likely
 * to yield significantly better space and time performance by
 * caching frequently requested values.
 *
 * This method will always cache values in the range -128 to 127,
 * inclusive, and may cache other values outside of this range.
 *
 * @param  i an {@code int} value.
 * @return an {@code Integer} instance representing {@code i}.
 * @since  1.5
 */
public static Integer valueOf(int i) {
    assert IntegerCache.high >= 127;
    if (i >= IntegerCache.low && i <= IntegerCache.high)
        return IntegerCache.cache[i + (-IntegerCache.low)];
    return new Integer(i);
}

i >= -128 && i <= 127 Integer.valueOf(i) i IntegerCachestatic final Integer cache[]:

IntegerCache.cache[i + (-IntegerCache.low)]

:

Integer a = 1; 
Integer b = 1;

a b a == b

byte 8

short 16

int 32

long 64

float 32IEEE 754

double 64 IEEE 754

boolean

char 16 Unicode

@CHENG CharactergetNumericValue(char ch)

Unicode int

A-Z '\u0041' '\u005A''\u0061' '\u007A''\uFF21' '\uFF3A' '\uFF41' '\uFF5A' 10 35 Unicode char  

361-9_A-Z A=10 Z=25

-1 -2