Java中的 Reader read(CharBuffer) 方法和示例

Java中Reader类的read(CharBuffer)方法用于将指定的字符读入 CharBuffer 实例。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(CharBuffer charBuffer)

参数：此方法接受一个强制参数charBuffer ，它是要写入 Stream 中的 CharBuffer 实例。

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。
• NullPointerException:如果要填充的 CharBuffer 实例为 null
• ReadOnlyBufferException:如果要填充的 CharBuffer 实例是只读缓冲区

下面的方法说明了 read(CharBuffer) 方法的工作：

方案一：

// Java program to demonstrate
// Reader read(CharBuffer) method
  
import java.io.*;
import java.util.*;
import java.nio.CharBuffer;
  
class GFG {
    public static void main(String[] args)
    {
  
        try {
  
            String str = "GeeksForGeeks";
  
            // Create a Reader instance
            Reader reader
                = new StringReader(str);
  
            // Get the CharBuffer instance
            // to be read from the stream
            CharBuffer charBuffer
                = CharBuffer.allocate(5);
  
            // Read the charBuffer
            // to this reader using read() method
            // This will put the str in the stream
            // till it is read by the reader
            reader.read(charBuffer);
  
            // Print the read charBuffer
            System.out.println(charBuffer
                                   .flip()
                                   .toString());
  
            reader.close();
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出：

Geeks

方案二：

// Java program to demonstrate
// Reader read(CharBuffer) method
  
import java.io.*;
import java.util.*;
import java.nio.CharBuffer;
  
class GFG {
    public static void main(String[] args)
    {
  
        try {
  
            String str = "GeeksForGeeks";
  
            // Create a Reader instance
            Reader reader
                = new StringReader(str);
  
            // Get the CharBuffer instance
            // to be read from the stream
            CharBuffer charBuffer
                = CharBuffer
                      .allocate(
                          str.length());
  
            // Read the charBuffer
            // to this reader using read() method
            // This will put the str in the stream
            // till it is read by the reader
            reader.read(charBuffer);
  
            // Print the read charBuffer
            System.out.println(charBuffer
                                   .flip()
                                   .toString());
  
            reader.close();
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出：

GeeksForGeeks

参考： https://docs.oracle.com/javase/9/docs/api/ Java/io/Reader.html#read-java.nio.CharBuffer-