Java Java.io.PushbackReader用法及代碼示例

java.io.PushbackReader 是一個字符流讀取器類，它允許將字符推回流中。

聲明：

public class PushbackReader
   extends FilterReader

構造函數：

• PushbackReader(閱讀器推送)：創建一個新的推回讀取器 - “push” 並帶有字符推回緩衝區。
• PushbackReader(讀卡器推送，int大小)：創建一個具有特定大小的推回緩衝區的新推回讀取器。

PushbackReader類的方法：

• read():java.io.PushbackReader.read()讀取單個字符。
  Syntax :

  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.

• 讀取(char[] carray，int 偏移量，int maxlen)：java.io.PushbackReader.read(char[] carray, int offset, int maxlen)讀取字符數組的某些部分
  Syntax :

  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()關閉 PushbackReader 並將與此流關聯的係統資源釋放到垃圾Collector。
  Syntax :

  public void close()
  Parameters :
  ------
  Return : 
  void
  Exception :
  ->  IOException : If I/O error occurs.

• 標記(int arg)：java.io.PushbackReader.mark(int arg)標記 PushbackReader 的當前位置。對於 PushbackReader，此方法總是拋出異常。
  Syntax :

  public void mark(int arg)
  Parameters :
  arg : integer specifying the read limit of the Stream
  Return : 
  void

• 跳過(長字符)：java.io.PushbackReader.skip(長字符)跳過並丟棄‘char’號。 PushbackReader 數據中的字符數。
  Syntax :

  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()方法調用。它將 PushbackReader 重新定位到標記位置。對於 PushbackReader，此方法總是拋出異常。
  Syntax :

  public void reset()
  Parameters :
  ----
  Return : 
  void
  Exception :
  ->  IOException : If I/O error occurs.
  

• markSupported():java.io.PushbackReader.markSupported()告知此流是否支持 mark() 操作，但它不支持。
  Syntax :

  public boolean markSupported()
  Parameters :
  -------
  Return : 
  true if PushbackReader supports the mark() method  else,false

• ready():java.io.PushbackReader.ready()告知流是否已準備好讀取
  Syntax :

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

• 未讀(int char)：java.io.PushbackReader.unread(int char)將單個字符推入推回緩衝區。在此方法返回後，要讀取的下一個字符將具有 (char)char 值。

  用法:

  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.
  

• 未讀(char[] carray)：java.io.PushbackReader.unread(char[] carray)將字符數組推送到 Pushback 緩衝區。被壓入的數組的索引從 0 開始。
  Syntax :

  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.
  

解釋PushbackReader方法的Java代碼：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"); 
  
        } 
    } 
} 

輸出：

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