FileDescriptor类valid()方法 (FileDescriptor Class valid() method)

• valid() method is available in java.io package.

  valid()方法在java.io包中可用。

• valid() method is used to check whether this FileDescriptor object is valid or not.

  valid()方法用于检查此FileDescriptor对象是否有效。

• valid() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.

  valid()方法是一个非静态方法，只能通过类对象访问，如果尝试使用类名称访问该方法，则会收到错误消息。

• valid() method does not throw an exception at the time of checking the status of an object.

  在检查对象状态时， valid()方法不会引发异常。

Syntax:

句法：

public boolean valid();

Parameter(s):

参数：

• It does not accept any parameter.

  它不接受任何参数。

Return value:

返回值：

The return type of the method is boolean, it returns true when this FileDescriptor is valid otherwise it returns false.

方法的返回类型为boolean ，如果此FileDescriptor有效，则返回true ，否则返回false 。

Example:

例：

// Java program to demonstrate the example // of boolean valid() method of FileDescriptorimport java.io.*;public class ValidOfFD {
    public static void main(String[] args) throws Exception {
     FileInputStream is_stm = null;  try {
      // Instantiates FileInputStream    is_stm = new FileInputStream("D:\\includehelp.txt");   // By using getFD() method is to get   // the file descriptor   FileDescriptor file_des = is_stm.getFD();   System.out.println("is_stm.getFD(): " + file_des);   // By using valid() method is to check    // whether the file descriptor is valid or   // not   boolean status = file_des.valid();   System.out.println("is_stm.valid(): " + status);  } catch (Exception ex) {
      System.out.println(ex.toString());  } finally {
      // with the help of this block is to   // free all necessary resources linked   // with the stream   if (is_stm != null) {
       is_stm.close();   }  } }}

Output

输出量

is_stm.getFD(): is_stm.valid(): true

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