编写一个程序测试大文件随机访问时三种访问模式的效率，三种模式使用类似的程序框架，只是产生文件对象的时候使用不同的模式。产生一个50M的大文件dummy，作为测试的数据文件。-The preparation of a program to test large file random access mode, when the efficiency of the three visits, the three models using the framework of a similar procedure, but have a document object model using a different time. 50M to produce a large file of dummy, as the test data files.