题目：**18.30 (找出单词)

编写一个程序，递归地找出某个目录下的所有文件中某个单词出现的次数。从命令行如下传递参数：

java Exercise18_30 dirName word

• 习题思路

1. （读取路径方法）和18.28题差不多，把找到文件后变量计数+1改成调用读取文件单词在文件内出现的次数即可（调用读取文件方法）。Java语言程序设计基础篇_编程练习题*18.28 (非递归目录大小)-CSDN博客
2. （读取文件方法）传入文件和单词，逐行读取文件，如果找到单词，则计数变量+1.
3. （main方法）读取传入的路径和单词，调用读取路径方法。

• 代码示例 

编程练习题18_30WordCount.java

package chapter_18;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class 编程练习题18_30WordCount {
	public static void main(String[] args) throws FileNotFoundException{
		if(args.length != 2) {
			System.out.println("Usage: java 编程练习题18_30WordCount dirName word");
			System.exit(0);
		}
		String path = args[0];
		String word = args[1];
		
		File file = new File(path);
		int count = readPath(file, word);
		System.out.println("The string "+word+" appears a total of "+count+" times.");
	}
	public static int readPath(File file,String word) throws FileNotFoundException{
		int count = 0;
		ArrayList<File> files = new ArrayList<File>();
		files.add(file);
		while(!files.isEmpty()) {
			ArrayList<File> newList = new ArrayList<File>();
			for(File f : files) {
				if(f.isFile())
					count+=readFile(f, word);
				else {
					File[] fileList = f.listFiles();
					if(fileList != null) {
						for(File f2:fileList){
							if(f2.isDirectory())
								newList.add(f2);
							else count += readFile(f2, word);
						}
					}
				}
			}
			files = newList;
		}
		return count;
	}
	public static int readFile(File file,String word)throws FileNotFoundException {
		int count = 0;
		try(Scanner input = new Scanner(file)){
			while(input.hasNextLine()) {
				String line = input.nextLine();
				if(line.contains(word))
					count++;
			}
		}
		return count;
		
	}

}

• 输出结果 

javac 编程练习题18_30WordCount.java

java chapter_18/编程练习题18_30WordCount C:/Users/Lenovo/eclipse-workspace/JavaFX/src public