Java.io.PushbackReader Java中的类

Java 中的 io.PushbackReader 类

Java.io.PushbackReader是一个字符流读取器类，它允许将字符推回流中。

宣言：

public class PushbackReader
   extends FilterReader

构造函数：

PushbackReader(Reader push) :创建一个新的 Pushback Reader – “push” 带有一个字符Pushback 缓冲区。
PushbackReader(Reader push, int size) ：使用特定大小的 Pushback 缓冲区创建一个新的 Pushback Reader。

PushbackReader 类的方法：

read() : Java.io.PushbackReader.read()读取单个字符。
句法：

public int read()
Parameters :
-----------
Return : 
reads single character from the Pushback buffer 
else, -1 i.e. when end of file is reached.
Exception :
->  IOException : If I/O error occurs.

read(char[] carray, int offset, int maxlen) : Java.io.PushbackReader.read(char[] carray, int offset, int maxlen)读取字符数组的某些部分
句法：

public int read(char[] carray, int offset, int maxlen)
Parameters :
carray : destination buffer to be read into
offset : starting position of the carray
maxlen : maximum no. of characters to be read
Return : 
reads some portion of the character array
else, -1 i.e. when end of file is reached.
Exception :
->  IOException : If I/O error occurs.

close() : Java.io.PushbackReader.close()关闭 PushbackReader 并将与此流相关的系统资源释放到垃圾收集器。
句法：
```
public void close()
Parameters :
------
Return : 
void
Exception :
->  IOException : If I/O error occurs.
```
mark(int arg) : Java.io.PushbackReader.mark(int arg)标记 PushbackReader 的当前位置。对于 PushbackReader，此方法总是抛出异常。
句法：
```
public void mark(int arg)
Parameters :
arg : integer specifying the read limit of the Stream
Return : 
void
```

skip(long char) : Java.io.PushbackReader.skip(long char)跳过并丢弃'char'号。 PushbackReader 数据中的字符数。
句法：

public long skip(long char)
Parameters : 
char : no. of bytes of PushbackReader data to skip.
Return : 
no. of bytes to be skipped
Exception: 
-> IOException : in case I/O error occurs

reset() : Java.io.PushbackReader.reset()由 mark() 方法调用。它将 PushbackReader 重新定位到标记的位置。对于 PushbackReader，此方法总是抛出异常。
句法：
```
public void reset()
Parameters :
----
Return : 
void
Exception :
->  IOException : If I/O error occurs.
```
markSupported() : Java.io.PushbackReader.markSupported()判断此流是否支持 mark() 操作，但它不支持。
句法：
```
public boolean markSupported()
Parameters :
-------
Return : 
true if PushbackReader supports the mark() method  else,false
```

ready() : Java.io.PushbackReader.ready()告诉流是否准备好被读取
句法：

public boolean ready()
Parameters :
-------
Return : 
true if the stream is ready to be read else,false

unread(int char) : Java.io.PushbackReader.unread(int char)将单个字符推送到 Pushback 缓冲区。在此方法返回后，要读取的下一个字符将具有 (char)char 值。
句法：
```
public void unread(int char)
Parameters :
char : int value of the character to be pushed back
Return : 
void
Exception :
->  IOException : If I/O error occurs or Pushback buffer is full.
```

unread(char[] carray) : Java.io.PushbackReader.unread(char[] carray)将一个字符数组推送到 Pushback 缓冲区。被推送的数组的索引将从 0 开始。
句法：

public void unread(char[] carray)
Parameters :
carray : character array to be pushed back
Return : 
void
Exception :
->  IOException : If I/O error occurs or Pushback buffer is full.

解释 PushbackReader 方法的Java代码：read(char[] carray)、close()、markSupported()、read()、mark()、ready()、skip()、unread()

// Java program illustrating the working of PushbackReader
// read(char[] carray), close(), markSupported()
// read(), mark(), ready(), skip(), unread()
  
import java.io.*;
public class NewClass
{
    public static void main(String[] args) throws IOException
    {
        try
        {
            // Initializing a StringReader and PushbackReader
            String s = "GeeksForGeeks";
  
            StringReader str_reader = new StringReader(s);
            PushbackReader geek_pushReader1 = new PushbackReader(str_reader);
            PushbackReader geek_pushReader2 = new PushbackReader(str_reader);
  
            // Use of ready() method :
            System.out.println("Is stream1 ready : " + geek_pushReader1.ready());
            System.out.println("Is stream2 ready : " + geek_pushReader2.ready());
  
            // Use of read() :
            System.out.println("\nWe have used skip() method in 1 : ");
            System.out.print("\nUse of read() in 1 : ");
            for (int i = 0; i < 6; i++)
            {
                char c = (char) geek_pushReader1.read();
                System.out.print(c);
  
                // Use of skip() :
                geek_pushReader1.skip(1);
            }
            System.out.println("");
  
            // USing read() :
            char[] carray = new char[20];
            System.out.println("Using read() in 2 : " + geek_pushReader2.read(carray));
  
  
            // USe of markSupported() :
   System.out.println("\nIs mark supported in 1  : " + geek_pushReader1.markSupported());
  
            geek_pushReader2.unread('F');
  
            // read the next char, which is the one we unread
            char c3 = (char) geek_pushReader2.read();
            System.out.println("USe of unread() : " + c3);
  
            // USe of mark() :
            geek_pushReader1.mark(5);
  
            // Use of close() :
            geek_pushReader1.close();
  
        }
        catch (IOException excpt)
        {
            System.out.println("mark not supported in 1");
  
        }
    }
}

输出：

Is stream1 ready : true
Is stream2 ready : true

We have used skip() method in 1 : 

Use of read() in 1 : GesoGe
Using read() in 2 : 1

Is mark supported in 1 : false
USe of unread() : F
mark not supported in 1