java - Why is upcasting a Class considered an unsafe operation? -

-

class कास्ट करते समय जावा कम्पाइलर एक "अनचाहे डाली" चेतावनी क्यों चालू करता है? ऑब्जेक्ट & gt; से क्लास & lt; ऑब्जेक्ट & gt; को बढ़ाता है? यह कैसे संभवतः असफल हो सकता है?

ऐसा कोई कलाकार केवल सामान्य रूप से सुरक्षित नहीं है सामान्य में , और तथ्य यह है कि यह वर्ग वर्ग के लिए सुरक्षित है। इस तरह से एक वर्ग की कल्पना करें: 

  // हाइफोटीटीकल! क्लास मायक्लास & lt; T & gt; वर्ग & lt; T & gt; {सार्वजनिक टी कुछ अंतर; }   
 अब, यदि प्रश्न में डालने की अनुमति दी गई थी, तो आप  
  MyClass & lt; Integer & gt; MyClassWithInteger = नया MyClass & lt; पूर्णांक & gt; (); MyClassWithInteger.someInstance = someInteger; // यह मान्य MyClass & lt ;? वस्तु & gt; फैली हुई है MyClassWithWildcard = myClassWithInteger; // यह मान्य नहीं है, लेकिन मान लें कि यह था: MyClass & lt; Object & gt; MyClassWithObject = myClassWithWildcard; // यह मान्य होगा, क्योंकि 'कुछ इन्स्टेंस' प्रकार 'ऑब्जेक्ट' का था, यहाँ myClassWithObject.someInstance = "someString"; // यह मान्य है लेकिन अनियंत्रित कलाकारों के माध्यम से, हमने चुपचाप / इस घटना के रूप में एक STRING में चुपचाप किया। तो यह असफल हो जायेगा: पूर्णांक I = myClassWithInteger.someInstance;   
 आपने टिप्पणी में पूछा:  
 
 क्या आप कह रहे हैं कि भाषा लेखकों को कक्षाओं की तरह सुरक्षित वर्गों के लिए विशेष उपचार से बचना चाहिए बोर्ड?   
 हां महत्वपूर्ण मुद्दा यह है कि इस तरह का एक कलाकार सुरक्षित है या नहीं यह सवाल है कि कक्षा के  शब्दों  पर निर्भर करता है सुरक्षा का पता नहीं लगाया जा सकता है  वाक्यविन्यास ।

Comments

Post a Comment

Popular posts from this blog

sql - Postgresql record to array -

-
I need to change back into an array to change lines from the array and filter the records. I am using info_schema._pg_expandarray in a SELECT query to get a line copy value in the array. Looking at the following array: "four" [] {i, i, o, t, b} _pg_expandarray leaves 5 rows with 1 row type record: records (I, 1) (i, 2) (o, 3) (t, 4) I have to filter this result set 't' to exclude record records. How can I do this? Should I convert back to the array? What is a way to filter the array directly? Thanks in advance. If your purpose is to create one set of the above rows, but remove the 't' in the line So, this is the trick: test => Information (i), 'o', 't', 'b' i. N --- --- --- i | 1 mother 2 o | 3b 5 (4 lines) As a side, unless you specifically want to return the index as a second column, then I unnest () information_schema._pg_expandarray () , which does not appear in the document and is probably...
Read more

c++ - Cmake produces file extensions in static library archives -

-
I have recently switched to autotools to cement, since the limiter cross platform is better for development and what I saw When I build a stable library of my C ++ code, all the files inside .cpp.o is a suffix ar income tax PA8 / libgenericTZR.a genericTZR.cpp.o I have seen other libraries made by other tools and they do not do it, I'm not sure this is the realm And there is a bad thing, but how can I create static libraries without cpp file extension? This is my CMake file add_executable (PA8 ISP_Charges.cpp genericTZR.cpp genericTZR.h) set (LIBSRC genericTZR.c genericTZR.h) add_library (genericTZR shared $ {LIBSRC}) add_library (genericTZR shared $$ TARGET_OBJECTS: myObjects & gt;) install add_library (Generic TZR-static static $ {LIBSRC}) set_target_properties (Generic TZR-Static Properties OUTPUT_NAME $ install (TARGETS PA8 DESTINATION BIN) TARGETS GENICTZR GENERICTZR-STATIC DESTINATION lib) Installed (files "$ {PROJECT_BINARY_DIR} /PA8/genericTZR.h...
Read more

Pygame memory leak with transform.flip -

-
Today I came across an interesting issue which, by writing a small side scroller, instead of a sprite sheet, I was planning to use because I lacked a good "packer" for making phantom sheets (and honestly with patience and passion as it is only a test project). Anyway, I showed the animation running on the right of 8 PNG (with transparency). I considered it a good idea to prepare the flipped images to run on the left in the consultant, and the frame is not framed when the game is running (Flip actually consumes a lot of CPU like I Was measured). > To get access to the loop, I get the memory leak self.move_l = [# 8 PNG images with transparency to the right] For the self in IMG. Move_l: self.move_r.append (pygame.transform.flip (img, true, false) error traceback: traceback (most recent Call final): The file "D: \ Python 34 \ _Projects \ efg \ efg.py", in line 196, in the & lt; module & gt; main = master program ((1024, 680)) "D: \ Python ...
Read more