Java Reader mark()用法及代碼示例

Reader類mark()方法

• mark() 方法可在java.io包。
• mark() 方法用於設置此流中的當前位置。當我們調用 reset() 方法時，它會將流重置為 mark() 方法最近設置的位置。
• mark() 方法是一個非靜態方法，它隻能通過類對象訪問，如果我們嘗試使用類名訪問方法，那麽我們將得到一個錯誤。
• mark() 方法可能會在標記流時拋出異常。
  IOException: 獲取任何輸入/輸出錯誤或不支持 seek() 方法時可能會拋出此異常。

用法:

    public void mark(int r_limit);

參數：

• int r_limit– 表示在標記失效之前可以讀取的字符數的限製。

返回值：

該方法的返回類型是void，它什麽都不返回。

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();
            }
        }
    }
}

輸出

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:!