JDK源码分析：Short.java

　　Short是基本数据类型short的包装类。

　　1）声明部：

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）私有静态内部类

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类加载的时候，加载该内部类，内部类静态模块代码执行，初始化缓存对象数组。

　　3）Short初始化方法：

　　通过构造函数初始化，构造函数如下：

//构造函数方法重载
public Short(String s) throws NumberFormatException {
    this.value = parseShort(s, 10);
}
//构造函数方法重载
public Short(short value) {
    this.value = value;
}

　　通过调用转换的方法，该系列方法如下：

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);
}

　　观察代码之间的调用关系。第一个方法返回short类型，第五个方法通过取缓存获得Short对象。

　　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

　　结论：同Byte.class分析，short类型自动装箱会去获取缓存的对象（-128~127）；使用构造函数初始化new，是一个新的对象，不从缓存里去获取对象。

　　4）其他方法

//解码，将short范围内的二进制，八进制，十六进制转换为十进制
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
//高位低位反转 正数
Short s7 = 2;
Short s8 = Short.reverseBytes(s7);
Out.println(s8);//512
//负数
short s_3 = (short)-0B000000000000011;//符号位直接使用符号替代，声明使用原码，运算时候使用补码，根据运算结果得出补码，再转为原码
short s_4 = (short)-0B000001000000001;
Out.println(s_4 == Short.reverseBytes(s_3));//true

　　5）属性：

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

原文地址：https://www.cnblogs.com/knsbyoo/p/9032471.html