掌握 Java 语言的字符串处理、文本文件的读写。
编写一个类名为 JavaCodeAnalyzer 的类，实现以下功能：
<1> 该类可以以一个 Java 源程序文件名创建一个对象，如果文件不存在，或扩展名不
是“ .java”，应提示文件错误；
<2> 对该源程序文件进行分析其中的： 代码行数、注释行数和空行数。
<3> 统计并按从多到少输出出现次数最多的 5 个关键字及其出现次数。
<4> 统计分析的结果输出到名为： result.txt 的文本文件中。
<5> 测试时要通过以 Java7 的 String 类的源码测试。(Master the string processing of Java language, read and write text files.
Write a class named JavaCodeAnalyzer to implement the following functions:
<1> this class can create an object with a Java source file name, if the file does not exist, or the extension does not
It is ".Java" and should be prompted for file errors;
<2> analyzes the source file: code line number, number of annotation lines, and empty line number.
<3> statistics and the most frequent occurrences of 5 key words and their occurrences from many to less.
The result of <4> statistical analysis is exported to the text file named result.txt.
<5> test through the Java7 String class source test.)