This instruction gets value from a non static field of the object on the top of the stack. field-spec is composed of two parts, a classname and field name (f.e. foo/bar/ClassName/fieldName). descriptor is the Java type descriptor of the field.
This instruction gets value from a static field of the object on the top of the stack. field-spec is composed of two parts, a classname and field name (f.e. foo/bar/ClassName/fieldName). descriptor is the Java type descriptor of the field.