编写一个程序，将 d:\java 目录下的所有.java 文件复制到 d:\jad 目录下，并 目录下，并 将原来文件的扩展名从 将原来文件的扩展名从.java 改为.ja

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这个主要是用到了File.listFile()的参数FilenameFilter()这个接口的accept()方法，该方法作用是根据过滤条件查找对应的File数组。

package com.testfilecopy;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FilenameFilter;
import java.io.IOException;

public class FileCopy {
	public static void main(String[] args) throws IOException {
		String src = "d:/java";
		File file = new File(src);
		if (!file.exists()) {
			throw new FileNotFoundException("目录不存在");
		}
		File[] files = file.listFiles(new FilenameFilter() {

			@Override
			public boolean accept(File dir, String name) {
				return name.endsWith(".java");
			}
		});
		System.out.println(files.length);
		File deskdir = new File("d:/jad");
		if (!deskdir.exists()) {
			deskdir.mkdir();
		}
		for (File file2 : files) {
			FileInputStream fis = new FileInputStream(file2);
			String destFileName = file2.getName().replace(".java", ".jad");
			System.out.println(destFileName);
			FileOutputStream fos = new FileOutputStream(new File(deskdir,destFileName));
			copy(fis, fos);
			fis.close();
			fos.close();
			System.out.println("复制完成");
		}
	}

	private static void copy(FileInputStream fis, FileOutputStream fos)
			throws IOException {
		int len = 0;
		byte[] bytes = new byte[1024];
		while ((len = fis.read(bytes)) != -1) {
			fos.write(bytes, 0, len);
		}

	}
}