Java中的 PushbackReader read(char, int, int) 方法和示例

Java中PushbackReader类的read(char[], int, int)方法用于将指定长度的字符读入指定偏移量的数组中。此方法阻塞流直到：

• 它从流中获取了一些输入。
• 发生了一些 IOException
• 它在读取时已到达流的末尾。

句法：

public int read(char[] charArray, 
                     int offset, 
                     int length) 

参数：此方法接受三个强制参数：

• charArray是要写入 Stream 的字符数组。
• 偏移量，它是要在数组中写入字符的偏移量索引。
• length是要写入数组的字符数。

返回值：此方法返回一个整数值，它是从流中读取的字符数。如果没有读取任何字符，则返回 -1。

异常：此方法抛出以下异常：

• IOException：如果输入输出时发生错误。
• IndexOutOfBoundsException:如果偏移值不在字符数组范围内

下面的方法说明了 read(char[], int, int) 方法的工作：

方案一：

// Java program to demonstrate
// PushbackReader read(char, int, int) method
  
import java.io.*;
import java.util.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        try {
            // Initializing a StringReader
            // and PushbackReader
            String s = "GeeksForGeeks";
  
            StringReader stringReader
                = new StringReader(s);
            PushbackReader pushbackReader
                = new PushbackReader(stringReader);
  
            // Get the character array
            // to be read from the stream
            char[] charArray = new char[5];
  
            // Get the offset index
            int offset = 0;
  
            // Get the length
            int length = 5;
  
            // Read the charArray
            // to this reader using read() method
            // This will put the str in the stream
            // till it is read by the reader
            pushbackReader
                .read(charArray, offset, length);
  
            // Print the read charArray
            System.out.println(
                Arrays.toString(charArray));
  
            // Close the stream
            pushbackReader.close();
            System.out.println("Stream Closed.");
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出：

[G, e, e, k, s]
Stream Closed.

方案二：

// Java program to demonstrate
// PushbackReader read(char, int, int) method
  
import java.io.*;
import java.util.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        try {
            // Initializing a StringReader
            // and PushbackReader
            String s = "GFG";
  
            StringReader stringReader
                = new StringReader(s);
            PushbackReader pushbackReader
                = new PushbackReader(stringReader);
  
            // Get the character array
            // to be read from the stream
            char[] charArray = new char[5];
  
            // Get the offset index
            int offset = 0;
  
            // Get the length
            int length = 2;
  
            // Read the charArray
            // to this reader using read() method
            // This will put the str in the stream
            // till it is read by the reader
            pushbackReader
                .read(charArray, offset, length);
  
            // Print the read charArray
            System.out.println(
                Arrays.toString(charArray));
  
            // Close the stream
            pushbackReader.close();
            System.out.println("Stream Closed.");
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出：

[G, F,,, ]
Stream Closed.

参考： https://docs.oracle.com/javase/9/docs/api/ Java/io/PushbackReader.html#read-char:A-int-int-