PushbackReader read() method in Java with Examples

2025年5月8日 | 阅读 4 分钟

在 Java 中，使用 PushbackReader 类的 read() 方法从流中读取单个字符。能够“取消读取”一个字符并在稍后重新处理它，使其可以用于顺序字符读取。此功能在需要前瞻或回溯的标记器或解析器中非常有用。除了 Reader 类的功能之外，PushbackReader 还通过启用一个小缓冲区来保存未读取的字符来扩展流读取。这种方法会阻止流，直到

它已包含一些流输入。
发生了一个 IOException。
它已经读到流的末尾。

语法

参数：上述方法不接受任何参数。

返回值：上面方法返回的值是从流中读取的整数值。可能范围是 0 到 65535。如果没有读取字符，则返回 -1。

异常：如果输入或输出过程中发生错误，上面的函数将引发 IOException。

示例 1

此代码演示了使用 PushbackReader 从字符串中读取字符。通过围绕 StringReader 的 PushbackReader，StringReader 作为底层流。read() 方法打印从流中依次检索的前八个字符的整数ASCII 值和匹配的字符。尽管没有利用 PushbackReader 的“回推”功能，但该应用程序展示了其逐字符读取功能。close() 方法处理沿途的异常，确保 reader 流被有效关闭。

实施

文件名： PushbackReaderExample1.java

import java.io.*; 
import java.util.*; 
public class PushbackReaderExample1
{ 
	public static void main(String[] args) 
	{ 
		try { 
			// Setting up a StringReader 
			// as well as PushbackReader 
			String str = "Hello World"; 
			StringReader stringReader = new StringReader(str); 
			PushbackReader pushbackReader = new PushbackReader(stringReader); 
			// Retrieve the character to be read from the stream. 
			int character; 
			//  Use the read() method to read the first five characters to this reader. 
			// This will insert the str in the stream till the reader reads it. 
			for (int i = 0; i < 8; i++) 
			{ 
				character = pushbackReader.read(); 
				System.out.println("\nThe Integer value " + "of the character read is: " + character); 
				System.out.println("The Actual " + "character read is: " + (char)character); 
			} 
			// Close the stream by using the read() 
			pushbackReader.close(); 
			System.out.println("The Stream is Closed."); 
		} 
		catch (Exception ex) { 
			System.out.println(ex); 
		} 
	} 
}   

输出

The Integer value of the character read is: 72
The Actual character read is: H
The Integer value of the character read is: 101
The Actual character read is: e
The Integer value of the character read is: 108
The Actual character read is: l
The Integer value of the character read is: 108
The Actual character read is: l
The Integer value of the character read is: 111
The Actual character read is: o
The Integer value of the character read is: 32
The Actual character read is:  
The Integer value of the character read is: 87
The Actual character read is: W
The Integer value of the character read is: 111
The Actual character read is: o
The Stream is Closed.

示例 2

该代码使用围绕 StringReader 的 PushbackReader 逐个读取字符串 "Hello World" 中的字符。使用 read() 方法一次检索一个字符，该方法输出匹配的字符和字符的整数（ASCII）值。由于循环读取的字符数等于输入字符串的长度 11 个，因此 reader 可以处理整个流。代码中使用 close() 方法来确保 reader 被正确关闭。然而，这个例子并没有利用 PushbackReader 的“回推”功能。通过处理异常来确保程序的稳定性。

实施

文件名： PushbackReaderExample2.java

import java.io.*; 
import java.util.*; 
public class PushbackReaderExample2
{ 
	public static void main(String[] args) 
	{ 
		try { 
			// Setting up a StringReader 
			// as well as PushbackReader 
			String str = "Hello World"; 
			StringReader stringReader = new StringReader(str); 
			PushbackReader pushbackReader = new PushbackReader(stringReader); 
			// Retrieve the character to be read from the stream. 
			int character; 
			//  Use the read() method to read the characters to this reader. 
			// This will insert the str in the stream till the reader reads it. 
			for (int i = 0; i < 11; i++) 
			{ 
				character = pushbackReader.read(); 
				System.out.println("\nThe Integer value " + "of the character read is: " + character); 
				System.out.println("The Actual " + "character read is: " + (char)character); 
			} 
			// Close the stream by using the read() 
			pushbackReader.close(); 
			System.out.println("The Stream is Closed."); 
		} 
		catch (Exception ex) { 
			System.out.println(ex); 
		} 
	} 
}   

输出

 
The Integer value of the character read is: 72
The Actual character read is: H
The Integer value of the character read is: 101
The Actual character read is: e
The Integer value of the character read is: 108
The Actual character read is: l
The Integer value of the character read is: 108
The Actual character read is: l
The Integer value of the character read is: 111
The Actual character read is: o
The Integer value of the character read is: 32
The Actual character read is:  
The Integer value of the character read is: 87
The Actual character read is: W
The Integer value of the character read is: 111
The Actual character read is: o
The Integer value of the character read is: 114
The Actual character read is: r
The Integer value of the character read is: 108
The Actual character read is: l
The Integer value of the character read is: 100
The Actual character read is: d
The Stream is Closed.

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