Java 中的 Java . io . pubackinputstream 类
原文:https://www . geesforgeks . org/Java-io-pubackinputstream-class-Java/
推回用于输入流，允许读取一个字节，然后将其返回(即“推回”)到流中。推回输入流类实现了这个想法。它提供了一种在不中断输入流的情况下“窥视”输入流的机制。 它扩展了 FilterInputStream。
字段:
-
受保护字节[] buf :这是推回缓冲区。 受保护的 int 位置–这是推回缓冲区内的位置，下一个字节将从该位置读取。 protected InputStream in – This is the input stream to be filtered.
施工人员:
- 推回输入流(输入流 in): 这将创建一个流对象，允许向输入流返回一个字节。 PushbackInputStream(InputStream in, int numBytes):* This creates a stream that has a pushback buffer that is numBytes long. This allows multiple bytes to be returned to the input stream.
方法:
-
int available(): 返回可以从此输入流读取(或跳过)的字节数的估计值，而不会被此输入流的方法的下一次调用阻塞。下一次调用可能是同一个线程或另一个线程。单次读取或跳过这么多字节不会阻塞，但可能会读取或跳过更少的字节。
```java Syntax: public int available() Returns: the number of bytes that can be read (or skipped over) from the input stream without blocking. Exception: IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
```
-
void close(): 关闭此输入流并释放与该流相关联的任何系统资源。一旦流被关闭，进一步的 read()、unread()、available()、reset()或 skip()调用将引发 IOException。关闭以前关闭的流没有效果。
```java Syntax: public void close() Returns: NA Exception: IOException - if an I/O error occurs.
```
-
布尔标记支持():测试该输入流是否支持标记和重置方法，但它不支持。
```java Syntax: public boolean markSupported() Returns: false, since this class does not support the mark and reset methods. Exception: NA
```
爪哇语言（一种计算机语言,尤用于创建网站)
```java // Java code illustrating available(), close() // and markSupported() methods
import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.PrintWriter; import java.io.PushbackInputStream;
public class PushbackInputStreamDemo { public static void main(String arg[]) throws IOException { PrintWriter pw = new PrintWriter(System.out, true); String str = "Hey geeks "; byte b[] = str.getBytes(); ByteArrayInputStream bout = new ByteArrayInputStream(b); PushbackInputStream push = new PushbackInputStream(bout);
// checking no. of bytes available pw.println("available bytes: " + push.available());
// checking if mark is supported pw.println("mark supported? :" + push.markSupported());
pw.close(); } } ```
输出:
```java available bytes: 10 mark supported? :false
```
-
int read(): 从此输入流中读取下一个字节的数据。值字节作为 0 到 255 范围内的 int 返回。如果因为已经到达流的末尾而没有字节可用，则返回值-1。此方法会一直阻塞，直到输入数据可用、检测到流的结尾或引发异常。
```java Syntax: public int read() Returns: the next byte of data, or -1 if the end of the stream has been reached. Exception: IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
```
-
int read(byte[] b，int off，int len): 从这个输入流中读取多达 len 个字节的数据到一个字节数组中。此方法首先读取任何推回的字节；此后，如果读取的字节少于 len 字节，则从底层输入流中读取。如果 len 不为零，则该方法阻塞，直到至少有 1 个字节的输入可用；否则，不读取字节，返回 0。
```java Syntax: public int read(byte[] b, int off, int len). Returns: the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached. Exception: NullPointerException - If b is null. IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
```
爪哇语言（一种计算机语言,尤用于创建网站)
```java // Java code illustrating read() method
import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.PrintWriter; import java.io.PushbackInputStream;
public class PushbackInputStreamDemo { public static void main(String arg[]) throws IOException { PrintWriter pw = new PrintWriter(System.out, true); String str = "GeeksforGeeks a computer science portal "; byte b[] = str.getBytes(); ByteArrayInputStream bout = new ByteArrayInputStream(b); PushbackInputStream push = new PushbackInputStream(bout);
int c; while((c=push.read())!=-1) { pw.print((char)c); } pw.println(); push.read(b, 0, 13); for(int i=0; i<13; i++) { pw.print((char)b[i]); } pw.println(); pw.close(); } } ```
输出:
```java GeeksforGeeks a computer science portal GeeksforGeeks
```
-
无效标记(int readlimit): 标记该输入流中的当前位置。 推回输入流的标记方法不做任何事情。
```java Syntax: public void mark(int readlimit) Returns: NA Exception: NA
```
-
void reset(): 将此流重新定位到上次在此输入流上调用 mark 方法时的位置。 类推回输入流的方法重置除了抛出一个 IOException 之外什么都不做。
```java Syntax: public void reset() Returns: NA Exception: IOException - if this method is invoked.
```
爪哇语言（一种计算机语言,尤用于创建网站)
```java // Java code illustrating mark() and reset() method
import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.PrintWriter; import java.io.PushbackInputStream;
public class PushbackInputStreamDemo { public static void main(String arg[]) throws Exception { PrintWriter pw = new PrintWriter(System.out, true); String str = "GeeksforGeeks a computer science portal "; byte b[] = str.getBytes(); ByteArrayInputStream bout = new ByteArrayInputStream(b); PushbackInputStream push = new PushbackInputStream(bout);
int c; while((c=push.read())!=-1) { pw.print((char)c); } pw.println();
// marking the position push.mark(5);
// reseting is not supported throw exception push.reset();
pw.close(); } } ```
输出:
```java GeeksforGeeks a computer science portal Exception in thread "main" java.io.IOException: mark/reset not supported at java.io.PushbackInputStream.reset(PushbackInputStream.java:364) at PushbackInputStreamDemo.main(PushbackInputStreamDemo.java:29)
```
-
void unread(byte[] b): 通过将字节数组复制到推回缓冲区的前面来推回字节数组。此方法返回后，下一个要读取的字节将具有值 b[0]，其后的字节将具有值 b[1]，依此类推。
```java Syntax: public void unread(byte[] b) returns: NA Exception: IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.
```
-
void unread(byte[] b，int off，int len): 通过将字节数组复制到推回缓冲区的前面来推回字节数组。此方法返回后，下一个要读取的字节将具有值 b[0]，其后的字节将具有值 b[1]，依此类推。
```java Syntax: public void unread(byte[] b,int off,int len) Returns: NA Exception: IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.
```
爪哇语言（一种计算机语言,尤用于创建网站)
```java // Java code illustrating unread() method
import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.PrintWriter; import java.io.PushbackInputStream;
public class PushbackInputStreamDemo { public static void main(String arg[]) throws Exception { PrintWriter pw = new PrintWriter(System.out, true); String str = "GeeksforGeeks a computer science portal "; byte b[] = str.getBytes(); ByteArrayInputStream bout = new ByteArrayInputStream(b); PushbackInputStream push = new PushbackInputStream(bout);
int c; while((c=push.read())!=-1) { pw.print((char)c); } pw.println();
// unread method push.unread(b); push.unread(b, 0, 6);
while((c=push.read())!=-1) { pw.print((char)c); } pw.println(); pw.close(); } } ```
输出:
```java GeeksforGeeks a computer science portal orGeeks a computer science portal
```
-
void unread(int b): 通过将一个字节复制到推回缓冲区的前面来推回该字节。此方法返回后，下一个要读取的字节将具有值(字节)b.
```java Syntax: public void unread(int b) Returns: NA Exception: IOException - If there is not enough room in the pushback buffer for the byte, or this input stream has been closed by invoking its close() method.
```
Java 语言（一种计算机语言,尤用于创建网站)
```java // java code illustrating unread() method
import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.PrintWriter; import java.io.PushbackInputStream;
public class PushbackInputStreamDemo { public static void main(String arg[]) throws Exception { PrintWriter pw = new PrintWriter(System.out, true); String str = "GeeksforGeeks a computer science portal "; byte b[] = str.getBytes(); ByteArrayInputStream bout = new ByteArrayInputStream(b); PushbackInputStream push = new PushbackInputStream(bout);
// unread method push.unread('A'); b[1] = (byte)push.read(); pw.println((char)b[1]); } } ```
输出:
```java A
```
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