Unsafe.putBoolean和Unsafe.puByte是native实现

putBoolean和putByte也是通过宏SET_FIELD模板出的函数

#define SET_FIELD(obj, offset, type_name, x) \
  oop p = JNIHandles::resolve(obj); \
  *(type_name*)index_oop_from_field_offset_long(p, offset) = truncate_##type_name(x)

unsafe.cpp中定义宏做truncate
#define truncate_jboolean(x) ((x) & 1)
#define truncate_jbyte(x) (x)
#define truncate_jshort(x) (x)
#define truncate_jchar(x) (x)
#define truncate_jint(x) (x)
#define truncate_jlong(x) (x)
#define truncate_jfloat(x) (x)
#define truncate_jdouble(x) (x)

综上：unsafe.Put*不会对值做修改
------------------------------------------------------------------------------------
getBoolean和getByte也是通过宏GET_FIELD模板出的函数

#define GET_FIELD(obj, offset, type_name, v) \
  oop p = JNIHandles::resolve(obj); \
  type_name v = *(type_name*)index_oop_from_field_offset_long(p, offset)

综上，unsafe.Get*不会对值做修改
------------------------------------------------------------------------------------
验证：
unsafe.putByte(foo, addr, (byte)2); // 设置为: 2
System.out.println(unsafe.getByte(foo, addr)); // 打印getByte: 2
System.out.println(unsafe.getBoolean(foo, addr)); // 打印getBoolean: true

unsafe.putByte(foo, addr, (byte)1); // 设置为: 1
System.out.println(unsafe.getByte(foo, addr)); // 打印getByte: 1
System.out.println(unsafe.getBoolean(foo, addr)); // 打印getBoolean: true
------------------------------------------------------------------------------------
疑问：
if(foo.flag)判断，使用getfield    Field flag:"Z"，执行逻辑等于：0 ！= flag
if(foo.getFlag())判断，使用invokevirtual    Method getFlag:"()Z"，执行逻辑等于： 0 != （(flag) & 1）

求大神帮忙解答

--------------------------
附getFlag jasm码：
public Method getFlag:"()Z"
    stack 1 locals 1
{
        aload_0;
        getfield    Field flag:"Z";
        ireturn;
}



https://gist.github.com/qudongfang/49635d86882c03e49cff2b0f7d833805

我替换成2和3,都只能打印出一个Hello Java为什么呢？下面是AsmTools反编译代码
super public class Foo
        version 52:0
{

static Field boolValue:Z;

public Method "<init>":"()V"
        stack 1 locals 1
{
                aload_0;
                invokespecial Method java/lang/Object."<init>":"()V";
                return;
}

public static Method main:"([Ljava/lang/String;)V"
        stack 2 locals 1
{
                iconst_2;
                putstatic Field boolValue:"Z";
                getstatic Field boolValue:"Z";
                ifeq L18;
                getstatic Field java/lang/System.out:"Ljava/io/PrintStream;";
                ldc String "Hello, Java!";
                invokevirtual Method java/io/PrintStream.println:"(Ljava/lang/String;)V";
        L18: stack_frame_type same;
                getstatic Field boolValue:"Z";
                iconst_1;
                if_icmpne L33;
                getstatic Field java/lang/System.out:"Ljava/io/PrintStream;";
                ldc String "Hello, JVM!";
                invokevirtual Method java/io/PrintStream.println:"(Ljava/lang/String;)V";
        L33: stack_frame_type same;
                return;
}

} // end Class Foo