IOS那些想当然的事

IOS里面有些看起来是那么回事，想起来也是那么回事，结果不是那么回事的事。

1.crash？##

代码片段1

  NSString *string = @"123";
  [string release];
  string = @"456";//crash?

代码片段2

  NSObject *object = [[NSObject alloc] init];
  [object release];
  [object doSomething];//crash?

代码片段3

  - (void)setupSomething {
      self.object = [[NSObject alloc] init];
      [self.object release];
      [self doSomething];   
  }

  - (void)doSomething {
          [self.object doSomething];//crash？
  }

2.equal？##

  NSString *str1 = @"123";
  NSString *str2 = @"123";
  BOOL eq1 = (str1 == str2); //NO?
  BOOL eq2 = [Str1 isEqual:str2];//YES?
  BOOL eq3 = [str1 isEqualToString:str2];//YES?

3.MD5？##

MD5加密？