Java 中的 Reader mark(int)方法，示例
原文:https://www . geesforgeks . org/reader-markint-method-in-Java-with-examples/
Java 中 Reader 类的 mark() 方法用于在调用 reset()后，将流标记为流读取将从其开始的检查点。Reader 类的所有子类都不支持此方法。
语法:
public void mark(int readAheadLimit)
参数:该方法接受一个强制参数 readAheadLimit ，它是在保留标记的同时可以读取的字符数的限制。读取这么多字符后，尝试重置流可能会失败。
返回值:此方法不返回值。
异常:如果在不支持输入输出或 mark()方法时出现一些错误，此方法将引发 IOException。
下面的方法说明了 mark()方法的工作原理:
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:
GeeksForGe
eks??
程序二:
// 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:
GeeksForGe
e
参考:https://docs . Oracle . com/javase/9/docs/API/Java/io/reader . html # mark-int-
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