JDK源碼分析：Short.java

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　　Short是基礎資料型別 (Elementary Data Type)short的封裝類。

　　1）聲明部：

public final class Short extends Number implements Comparable<Short> 

　　extends Number，override methods：

public abstract int intValue();    public abstract float floatValue();    public abstract long longValue();    public abstract double doubleValue();    public byte byteValue() {        return (byte)intValue();    }    public short shortValue() {        return (short)intValue();    }

　　implements Comparable<Short> ：

public int compareTo(Short anotherShort) {        return compare(this.value, anotherShort.value);    }

public static int compare(short x, short y) {        return x - y;    }

　　2）私人靜態內部類

private static class ShortCache {      private ShortCache(){}        static final Short cache[] = new Short[-(-128) + 127 + 1];        static {          for(int i = 0; i < cache.length; i++)              cache[i] = new Short((short)(i - 128));      }  }

　　Short類載入的時候，載入該內部類，內部類靜態模組代碼執行，初始化緩衝對象數組。

　　3）Short初始化方法：

　　通過建構函式初始化，建構函式如下：

//建構函式方法重載  public Short(String s) throws NumberFormatException {      this.value = parseShort(s, 10);  }  //建構函式方法重載  public Short(short value) {      this.value = value;  }

　　通過調用轉換的方法，該系列方法如下：

public static short parseShort(String s, int radix)      throws NumberFormatException {      int i = Integer.parseInt(s, radix);      if (i < MIN_VALUE || i > MAX_VALUE)          throw new NumberFormatException(              "Value out of range. Value:\"" + s + "\" Radix:" + radix);      return (short)i;  }  public static short parseShort(String s) throws NumberFormatException {      return parseShort(s, 10);  }  public static Short valueOf(String s, int radix)      throws NumberFormatException {      return valueOf(parseShort(s, radix));  }  public static Short valueOf(String s) throws NumberFormatException {      return valueOf(s, 10);  }  public static Short valueOf(short s) {      final int offset = 128;      int sAsInt = s;      if (sAsInt >= -128 && sAsInt <= 127) { // must cache          return ShortCache.cache[sAsInt + offset];      }      return new Short(s);} 

　　觀察代碼之間的調用關係。第一個方法返回short類型，第五個方法通過取緩衝獲得Short對象。

　　初始化例子：

short  s_1 = 1;  String str_1 = "1";  Short s1 = new Short(str_1);  Short s2 = new Short(s_1);  Short s3 = s_1;  Short s4 = Short.parseShort(str_1);  Short s5 = Short.valueOf(str_1);  s1 == s2;//fasle  s1 == s3;//fasle  s2 == s3;//fasle  s4 == s3;//true  s5 == s3;//true

　　結論：同Byte.class分析，short類型自動裝箱會去擷取緩衝的對象（-128~127）；使用建構函式初始化new，是一個新的對象，不從緩衝裡去擷取對象。

　　4）其他方法

//解碼，將short範圍內的二進位，八進位，十六進位轉換為十進位  public static Short decode(String nm) throws NumberFormatException {      int i = Integer.decode(nm);      if (i < MIN_VALUE || i > MAX_VALUE)          throw new NumberFormatException(                  "Value " + i + " out of range from input " + nm);      return valueOf((short)i);  }    public static String toString(short s) {      return Integer.toString((int)s, 10);  }  public String toString() {      return Integer.toString((int)value);  }    @Override  public int hashCode() {      return Short.hashCode(value);  }  public static int hashCode(short value) {      return (int)value;  }  public boolean equals(Object obj) {      if (obj instanceof Short) {          return value == ((Short)obj).shortValue();      }      return false;  }    public static int toUnsignedInt(short x) {      return ((int) x) & 0xffff;  }  public static long toUnsignedLong(short x) {      return ((long) x) & 0xffffL;  }  //Returns the value obtained by reversing the order of the bytes in the two‘s   //complement representation of the specified {@code short} value.  public static short reverseBytes(short i) {      return (short) (((i & 0xFF00) >> 8) | (i << 8));  }  

　　e.g：

short  s_1 = 1;  short s_2 = -1;  String str_2 = "0x21";  Short s6 = Short.decode(str_2);//33  Out.println(s6.toString());//33  Out.println(Short.toString(s6.shortValue()));//33  Out.println(s6.hashCode());//33  Out.println(Short.toUnsignedInt(s_1));//1  Out.println(Short.toUnsignedInt(s_2));//65535  Out.println(Short.toUnsignedLong(s_1));//1  Out.println(Short.toUnsignedLong(s_2));//65535  Out.println(s4.equals(s1));//true  //高位低位反轉 正數  Short s7 = 2;  Short s8 = Short.reverseBytes(s7);  Out.println(s8);//512  //負數  short s_3 = (short)-0B000000000000011;//符號位直接使用符號替代，聲明使用原碼，運算時候使用補碼，根據運算結果得出補碼，再轉為原碼  short s_4 = (short)-0B000001000000001;  Out.println(s_4 == Short.reverseBytes(s_3));//true 

　　5）屬性：

Out.println("MAX:" + Short.MAX_VALUE);  Out.println("MIN:" + Short.MIN_VALUE);  Out.println("BYTES:" + Short.BYTES);  Out.println("bit size:" + Short.SIZE);  Out.println("primitive type:" + Short.TYPE);    MAX:32767  MIN:-32768  BYTES:2  bit size:16  primitive type:short 

　　

JDK源碼分析：Short.java