Java PushbackReader mark()用法及代碼示例

PushbackReader類mark()方法

• mark() 方法可在java.io包。
• mark() 方法用於標記此流中的當前位置，此方法在調用期間拋出異常。
• 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：當此流不支持 mark() 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
// PushbackReader

import java.io.*;

public class MarkOfPBR {
    public static void main(String[] args) throws Exception {
        Reader r_stm = null;
        PushbackReader pb_r = null;
        try {
            // Instantiates Reader and PushbackReader
            r_stm = new StringReader("Java World!!!!");
            pb_r = new PushbackReader(r_stm);

            // By using read() method isto 
            // read the character from pb_r
            char ch1 = (char) pb_r.read();
            char ch2 = (char) pb_r.read();
            char ch3 = (char) pb_r.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
            // pb_r
            System.out.println("pb_r.mark(1):");
            pb_r.mark(1);
            char ch4 = (char) pb_r.read();
            char ch5 = (char) pb_r.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("pb_r.reset():");
            pb_r.reset();
            char ch6 = (char) pb_r.read();
            char ch7 = (char) pb_r.read();
            char ch8 = (char) pb_r.read();

            System.out.println("ch4:" + ch6);
            System.out.println("ch5:" + ch7);
            System.out.println("ch6:" + ch8);
        } catch (Exception ex) {
            System.out.println("Mark Not Supported");
        } finally {
            // with the help of this block is to
            // free all necessary resources linked
            // with the stream
            if (r_stm != null) {
                r_stm.close();
                if (pb_r != null) {
                    pb_r.close();
                }
            }
        }
    }
}

輸出

ch1:J
ch2:a
ch3:v
pb_r.mark(1):
Mark Not Supported