Java 中的 Java.io.Reader 类
这是一个用于读取字符流的抽象类。子类必须实现的唯一方法是 read(char[]、int、int)和 close()。然而,大多数子类将覆盖这里定义的一些方法,以便提供更高的效率、额外的功能或两者兼而有之。 施工人员:
- 受保护的读取器():创建一个新的字符流读取器,其关键部分将在读取器本身上同步。
- 受保护的读取器(对象锁):创建一个新的字符流读取器,其关键部分将在给定的对象上同步。
方法:
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抽象 void close() : 关闭流并释放与之关联的任何系统资源。一旦流被关闭,进一步的 read()、ready()、mark()、reset()或 skip()调用将引发 IOException。关闭以前关闭的流没有效果。
java Syntax :public abstract void close() throws IOException Throws: IOException
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空标记(int readAheadLimit) : 标记溪流中的当前位置。对 reset()的后续调用将尝试将流重新定位到这一点。并非所有字符输入流都支持 mark()操作。
java Syntax :public void mark(int readAheadLimit) throws IOException Parameters: readAheadLimit - Limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail. Throws: IOException
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布尔型 markSupported() : 告知此流是否支持 mark()操作。默认实现总是返回 false。子类应该重写此方法。
java Syntax :public boolean markSupported() Returns: true if and only if this stream supports the mark operation.
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int read() : 读取单个字符。此方法将一直阻塞,直到某个字符可用、出现输入/输出错误或到达流的末尾。 想要支持高效单字符输入的子类应该覆盖这个方法。
java Syntax :public int read() throws IOException Returns: The character read, as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream has been reached Throws: IOException
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int read(char[] cbuf) : 将字符读入数组。此方法将一直阻塞,直到有一些输入可用、出现输入/输出错误或到达流的末尾。
java Syntax :public int read(char[] cbuf) throws IOException Parameters: cbuf - Destination buffer Returns: The number of characters read, or -1 if the end of the stream has been reached Throws: IOException
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抽象 int read(char[] cbuf,int off,int len) : 将字符读入数组的一部分。此方法将一直阻塞,直到有一些输入可用、出现输入/输出错误或到达流的末尾。
java Syntax :public abstract int read(char[] cbuf, int off, int len) throws IOException Parameters: cbuf - Destination buffer off - Offset at which to start storing characters len - Maximum number of characters to read Returns: The number of characters read, or -1 if the end of the stream has been reached Throws: IOException
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int read(CharBuffer 目标):尝试将字符读入指定的字符缓冲区。缓冲区按原样用作字符存储库:所做的唯一更改是 put 操作的结果。不执行缓冲区的翻转或倒回。
java Syntax :public int read(CharBuffer target) throws IOException Parameters: target - the buffer to read characters into Returns: The number of characters added to the buffer, or -1 if this source of characters is at its end Throws: IOException NullPointerException ReadOnlyBufferException
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布尔就绪():告知该流是否准备好被读取。
java Syntax :public boolean ready() throws IOException Returns: True if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block. Throws: IOException
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无效重置():重置流。如果流已被标记,则尝试在标记处重新定位它。如果流没有被标记,那么尝试以适合特定流的方式重置它,例如通过将它重新定位到它的起点。并非所有字符输入流都支持 reset()操作,有些支持 reset(),但不支持 mark()。
java Syntax :public void reset() throws IOException Throws: IOException
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长跳过(长 n) : 跳过字符。此方法将一直阻塞,直到某些字符可用、出现输入/输出错误或到达流的末尾。
java Syntax :public long skip(long n) throws IOException Parameters: n - The number of characters to skip Returns: The number of characters actually skipped Throws: IllegalArgumentException - If n is negative. IOException
//Java program demonstrating Reader methods
import java.io.*;
import java.nio.CharBuffer;
import java.util.Arrays;
class ReaderDemo
{
public static void main(String[] args) throws IOException
{
Reader r = new FileReader("file.txt");
PrintStream out = System.out;
char c[] = new char[10];
CharBuffer cf = CharBuffer.wrap(c);
//illustrating markSupported()
if(r.markSupported()) {
//illustrating mark()
r.mark(100);
out.println("mark method is supported");
}
//skipping 5 characters
r.skip(5);
//checking whether this stream is ready to be read.
if(r.ready())
{
//illustrating read(char[] cbuf,int off,int len)
r.read(c,0,10);
out.println(Arrays.toString(c));
//illustrating read(CharBuffer target )
r.read(cf);
out.println(Arrays.toString(cf.array()));
//illustrating read()
out.println((char)r.read());
}
//closing the stream
r.close();
}
}
输出:
[f, g, h, i, g, k, l, m, n, o]
[p, q, r, s, t, u, v, w, x, y]
z
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