Java Reader mark()用法及代码示例

Reader类mark()方法

• mark() 方法可在java.io包。
• mark() 方法用于设置此流中的当前位置。当我们调用 reset() 方法时，它会将流重置为 mark() 方法最近设置的位置。
• mark() 方法是一个非静态方法，它只能通过类对象访问，如果我们尝试使用类名访问方法，那么我们将得到一个错误。
• mark() 方法可能会在标记流时抛出异常。
  IOException: 获取任何输入/输出错误或不支持 seek() 方法时可能会抛出此异常。

用法:

    public void mark(int r_limit);

参数：

• int r_limit– 表示在标记失效之前可以读取的字符数的限制。

返回值：

该方法的返回类型是void，它什么都不返回。

例：

// Java program to demonstrate the example 
// of void mark(int r_limit) method of Reader

import java.io.*;

public class MarkOfR {
    public static void main(String[] args) throws Exception {
        Reader r_stm = null;

        try {
            // Instantiates Reader
            r_stm = new StringReader("JavaWorld!!!!");

            // By using read() method isto 
            // read the character from r_stm
            char ch1 = (char) r_stm.read();
            char ch2 = (char) r_stm.read();
            char ch3 = (char) r_stm.read();

            System.out.println("ch1:" + ch1);
            System.out.println("ch2:" + ch2);
            System.out.println("ch3:" + ch3);

            // By using mark() method isto
            // set the current position in this
            // r_stm
            System.out.println("r_stm.mark(1):");
            r_stm.mark(1);
            char ch4 = (char) r_stm.read();
            char ch5 = (char) r_stm.read();

            System.out.println("ch4:" + ch4);
            System.out.println("ch5:" + ch5);

            // By using reset() method isto
            // reset the stream to the position 
            // set by the call mark() method
            System.out.println("r_stm.reset():");
            r_stm.reset();
            char ch6 = (char) r_stm.read();
            char ch7 = (char) r_stm.read();
            char ch8 = (char) r_stm.read();
            char ch9 = (char) r_stm.read();
            char ch10 = (char) r_stm.read();
            char ch11 = (char) r_stm.read();
            char ch12 = (char) r_stm.read();

            System.out.println("ch4:" + ch6);
            System.out.println("ch5:" + ch7);
            System.out.println("ch6:" + ch8);
            System.out.println("ch7:" + ch9);
            System.out.println("ch8:" + ch10);
            System.out.println("ch9:" + ch11);
            System.out.println("ch10:" + ch12);

        } catch (Exception ex) {
            System.out.println("Stream Closed Before!!!");
        } finally {
            // with the help of this block is to
            // free all necessary resources linked
            // with the stream
            if (r_stm != null) {
                r_stm.close();
            }
        }
    }
}

输出

ch1:J
ch2:a
ch3:v
r_stm.mark(1):
ch4:a
ch5:W
r_stm.reset():
ch4:a
ch5:W
ch6:o
ch7:r
ch8:l
ch9:d
ch10:!