Java Reader mark(int)方法及示例

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Java Reader mark(int)方法及示例

Java中Reader类的mark()方法是用来标记流的检查点，一旦调用reset()，流的读取将从这里开始。不是所有的Reader类的子类都支持这个方法。

语法。

public void mark(int readAheadLimit)

参数。该方法接受一个强制性参数readAheadLimit，它是在保留标记的情况下可以读取的字符数的限制。在读取这么多的字符后，试图重置流可能会失败。

返回值。该方法不返回任何值。

异常。如果在输入输出时发生一些错误或者mark()方法不被支持，该方法会抛出IOException。

下面的方法说明了mark()方法的工作。

程序 1:

// Java program to demonstrate// Reader mark() method  import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          try {              String str = "GeeksForGeeks";              // Create a Reader instance            Reader reader                = new StringReader(str);              // Get the character            // to be read from the stream            int ch;              // Read the first 10 characters            // to this reader using read() method            // This will put the str in the stream            // till it is read by the reader            for (int i = 0; i < 10; i++) {                ch = reader.read();                System.out.print((char)ch);            }              System.out.println();              // mark the stream for            // 5 characters using mark()            reader.mark(5);              // reset the stream position            reader.reset();              // Read the 5 characters from marked position            // to this reader using read() method            for (int i = 0; i < 5; i++) {                ch = reader.read();                System.out.print((char)ch);            }        }        catch (Exception e) {            System.out.println(e);        }    }}

输出:

GeeksForGeeks??

程序2。

// Java program to demonstrate// Reader mark() method  import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          try {            String str = "GeeksForGeeks";              // Create a Reader instance            Reader reader                = new StringReader(str);              // Get the character            // to be read from the stream            int ch;              // Read the first 10 characters            // to this reader using read() method            // This will put the str in the stream            // till it is read by the reader            for (int i = 0; i < 10; i++) {                ch = reader.read();                System.out.print((char)ch);            }              System.out.println();              // mark the stream for            // 10 characters using mark()            reader.mark(10);              // reset the stream position            reader.reset();              // Read the 1 characters from marked position            // to this reader using read() method            for (int i = 0; i < 1; i++) {                ch = reader.read();                System.out.print((char)ch);            }        }        catch (Exception e) {            System.out.println(e);        }    }}

输出: