Java 中的 BufferedReader mark()方法，带示例

原文:https://www . geeksforgeeks . org/bufferedeer-mark-method-in-Java-with-examples/

Java 中buffere reader类的 mark() 方法用于标记缓冲区读取器流中的当前位置。在调用了 mark()方法之后，同样的bufferedeeler类的 reset()方法也被调用。reset()方法将位置固定在最后标记的位置，以便可以再次读取相同的字节。

语法:

public void mark(int readAheadLimit) 
                   throws IOException

覆盖:覆盖阅读器类的 mark()方法。

参数:此方法接受整数类型的 readAheadLimit ，表示在标记位置无效之前可以读取的最大字节数限制。

返回值:此方法不返回值。

异常:这个方法可以抛出两种类型的异常。

  • IllegalArgumentException–如果传递的参数 readAheadLimit 小于零，将引发此异常。
  • io 异常–如果出现输入/输出错误，将引发该异常。

下面的程序说明了 IO 包中 BufferedReader 类中的 mark()方法。 程序 1: 假设文件“c:/demo.txt”的存在。

// Java program to illustrate
// BufferedReader mark() method

import java.io.*;

public class GFG {
    public static void main(String[] args)
    {

        // Read the stream 'demo.txt'
        // for containing text "GEEKS"
        FileReader fileReader
            = new FileReader(
                "c:/demo.txt");

        // Convert fileReader to
        // bufferedReader
        BufferedReader buffReader
            = new BufferedReader(
                fileReader);

        // Read and print characters
        // one by one
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());

        // Mark is set on the stream
        buffReader.mark(0);

        System.out.println(
            "Char : "
            + (char)buffReader.read());

        // Reset() is invoked
        buffReader.reset();

        // Read and print characters
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
    }
}

Output:

Char : G
Char : E
Char : E
Char : K
Char : K
Char : S

程序 2: 假设文件“c:/demo.txt”的存在。

// Java program to illustrate
// BufferedReader mark() method

import java.io.*;
public class GFG {
    public static void main(String[] args)
    {

        // Read the stream 'demo.txt'
        // containing text "GEEKSFORGEEKS"
        FileReader fileReader
            = new FileReader(
                "c:/demo.txt");

        // Convert fileReader to
        // bufferedReader
        BufferedReader buffReader
            = new BufferedReader(
                fileReader);

        // Read and print characters
        // one by one
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());

        // Mark is set on the stream
        buffReader.mark(0);

        System.out.println(
            "Char : "
            + (char)buffReader.read());

        // Reset() is invoked
        buffReader.reset();

        // read and print characters
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
        System.out.println(
            "Char : "
            + (char)buffReader.read());
    }
}

Output:

Char : G
Char : E
Char : E
Char : K
Char : S
Char : S
Char : F
Char : O
Char : R

参考文献: https://docs . Oracle . com/javase/10/docs/API/Java/io/bufferedeeler . html # mark(int)

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