java 文档删除不了file.delete();

File file = new File(EMP_DATA_FILE);
File file2 = new File("D:/eclipse-jee-mars-R-win32-x86_64/项目/HRMIS/records-new.txt");
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(file));
} catch (FileNotFoundException e2) {
// TODO Auto-generated catch block
e2.printStackTrace();
}
PrintWriter writer = null;
try {
writer = new PrintWriter(file2);
} catch (FileNotFoundException e2) {
// TODO Auto-generated catch block
e2.printStackTrace();
}
String line;
try {
while ((line = reader.readLine()) != null) {
// 判断条件，根据自己的情况书写，会删除所有符合条件的行
if (line.startsWith(payroll)) {
// 读取后面的几行,废弃
continue;
}
writer.println(line);
writer.flush();
}
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
reader.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
writer.close();

    // 删除老文件
    file.delete();
    file2.renameTo(file);
    System.out.print("\nRecord deleted.\n");

String cmd = "del "+ EMP_DATA_FILE ;
    Runtime run = Runtime.getRuntime(); 
    try { 
    Process p = run.exec("cmd /c "+cmd); //cmd为String，其内容为对应系统的删除命令，例如：在win下，应该写成：String cmd = "del "+你的文件路径以及文件名; 
    p.waitFor(); 
    } catch (Exception e) { 
    e.printStackTrace(); 
    }
    为什么把这段代码放在了这方法的开头就可以了，但该段程序并未删除文档，好像是把文档的各种流关闭了，然后再执行delete方法就可以删除了，求大神们解答下为什么啊？？？？？？？？，File的delete删除。到底要关闭那些流啊？？？？？