学习java笔记（2），java.lang.Byte。

Byte类型的SIZE是8，开始还以为是1呢。这个值是指使用的bit位数，而不是对象占内存大小。

Byte为有符号数，－128～127，初始化是初始值不能超过表示的范围，会抛异常，而不象C++会截断。

使用字符串类型初始化时，字符串不能为null或者""，否则会抛数字格式化异常。

 

package tjava.testlang;public class TestByte extends BasicClassTest{static String className = "java.lang.Byte";public static void test() throws ClassNotFoundException{logPrintln("Test Show:");logPrintln(" Byte(/"123/") = " + new Byte("123"));logPrintln(" Byte(/"-123/") = " + new Byte("-123"));try{logPrintln(" Byte(/"abc/") = " + new Byte("abc"));} catch (NumberFormatException e){logPrintln(" Byte(/"abc/") = new Byte(/"abc/") throw a NumberFormatException!");}logPrintln(" Byte((byte) (123)) = " + new Byte((byte) 123));try{logPrintln(" Byte.parseByte(null) = " + Byte.parseByte(null));} catch (NumberFormatException e){logPrintln(" Byte(null) = new Byte(null) throw a NumberFormatException!");}try{logPrintln(" Byte.parseByte(/"/") = " + Byte.parseByte(""));} catch (NumberFormatException e){logPrintln(" Byte(/"/") = new Byte(null) throw a NumberFormatException!");}try{logPrintln(" Byte.valueOf(null) = " + Byte.valueOf(null));} catch (NumberFormatException e){logPrintln(" Byte.valueOf(null) = new Byte(null) throw a NumberFormatException!");}logPrintln("Byte.parseByte(/"7b/", 16) = " + Byte.parseByte("7b", 16));logPrintln("Byte.parseByte(/"-7b/", 16) = " + Byte.parseByte("-7b", 16));logPrintln(" Byte.valueOf(/"7b/", 16) = " + Byte.valueOf("7b", 16));logPrintln(" Byte.valueOf(/"-7b/", 16) = " + Byte.valueOf("-7b", 16));logPrintln(" Byte.TYPE = " + Byte.TYPE);logPrintln(" Byte.SIZE = " + Byte.SIZE);logPrintln(" Byte.MAX_VALUE = " + Byte.MAX_VALUE);logPrintln(" Byte.MAX_VALUE+1 = " + new Byte((byte) (Byte.MAX_VALUE + (byte) 1)));logPrintln(" Byte.MIN_VALUE = " + Byte.MIN_VALUE);logPrintln(" Byte.MIN_VALUE-1 = " + new Byte((byte) (Byte.MIN_VALUE - (byte) 1)));}public static void showClassInfo() throws ClassNotFoundException{BasicClassTest.showClassInfo(className);}}

 

结果：

 

=================== java.lang.Byte's information ===================
    package name : java.lang
      class name : java.lang.Byte
super class name : java.lang.Number
  include method :
                   hashCode( )
                   compareTo( java.lang.Byte )
                   compareTo( java.lang.Object )
                   equals( java.lang.Object )
                   toString( byte )
                   toString( )
                   decode( java.lang.String )
                   valueOf( byte )
                   valueOf( java.lang.String int )
                   valueOf( java.lang.String )
                   byteValue( )
                   doubleValue( )
                   floatValue( )
                   intValue( )
                   longValue( )
                   shortValue( )
                   parseByte( java.lang.String )
                   parseByte( java.lang.String int )
                   wait( )
                   wait( long int )
                   wait( long )
                   getClass( )
                   notify( )
                   notifyAll( )
   include field :
                   MIN_VALUE
                   MAX_VALUE
                   TYPE
                   SIZE
include Constructor :
                   java.lang.Byte( byte )
                   java.lang.Byte( java.lang.String )
Test Show:
            Byte("123") = 123
           Byte("-123") = -123
            Byte("abc") = new Byte("abc") throw a NumberFormatException!
     Byte((byte) (123)) = 123
             Byte(null) = new Byte(null) throw a NumberFormatException!
             Byte("") = new Byte(null) throw a NumberFormatException!
     Byte.valueOf(null) = new Byte(null) throw a NumberFormatException!
Byte.parseByte("7b", 16)  = 123
Byte.parseByte("-7b", 16) = -123
  Byte.valueOf("7b", 16)  = 123
  Byte.valueOf("-7b", 16) = -123
              Byte.TYPE = byte
              Byte.SIZE = 8
         Byte.MAX_VALUE = 127
       Byte.MAX_VALUE+1 = -128
         Byte.MIN_VALUE = -128
       Byte.MIN_VALUE-1 = 127