Java.io.StreamTokenizer.pushBack() 方法

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  描述

  java.io.StreamTokenizer.pushBack() 方法将导致标记生成器的nextToken方法的下一个呼叫在Af - Ag型字段中返回的当前值，而不是在NVAL或SVAL字段修改的值。
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  声明

  以下是java.io.StreamTokenizer.pushBack()方法的声明。

   public void pushBack()

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  参数

  N/A
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  返回值

  此方法不返回值。
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  异常

  N/A
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  例子

  以下示例显示java.io.StreamTokenizer.pushBack()方法的用法。

   
  package com.jc2182;
  
  import java.io.*;
  
  public class StreamTokenizerDemo {
     public static void main(String[] args) {
        String text = "Hello. This is a text \n that will be split " 
           + "into tokens. 1 + 1 = 2";
           
        try {
           // create a new file with an ObjectOutputStream
           FileOutputStream out = new FileOutputStream("test.txt");
           ObjectOutputStream oout = new ObjectOutputStream(out);
  
           // write something in the file
           oout.writeUTF(text);
           oout.flush();
  
           // create an ObjectInputStream for the file we created before
           ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));
  
           // create a new tokenizer
           Reader r = new BufferedReader(new InputStreamReader(ois));
           StreamTokenizer st = new StreamTokenizer(r);
  
           // specify that numbers should be parsed
           st.parseNumbers();
  
           // print the stream tokens
           boolean eof = false;
           
           do {
              int token = st.nextToken();
  
              switch (token) {
                 case StreamTokenizer.TT_EOF:
                    System.out.println("End of File encountered.");
                    eof = true;
                    break;
                    
                 case StreamTokenizer.TT_EOL:
                    System.out.println("End of Line encountered.");
                    break;
                    
                 case StreamTokenizer.TT_WORD:
                    System.out.println("Word: " + st.sval);
                    break;
                    
                 case StreamTokenizer.TT_NUMBER:
                    System.out.println("Number: " + st.nval);
                    break;
                    
                 default:
                    System.out.println((char) token + " encountered.");
                    
                    if (token == '!') {
                       eof = true;
                    }
              }
  
              // pushback the last token
              st.pushBack();
  
              token = st.nextToken();
  
              switch (token) {
                 case StreamTokenizer.TT_EOF:
                    System.out.println("End of File encountered.");
                    eof = true;
                    break;
                    
                 case StreamTokenizer.TT_EOL:
                    System.out.println("End of Line encountered.");
                    break;
                    
                 case StreamTokenizer.TT_WORD:
                    System.out.println("Word: " + st.sval);
                    break;
                    
                 case StreamTokenizer.TT_NUMBER:
                    System.out.println("Number: " + st.nval);
                    break;
                    
                 default:
                    System.out.println((char) token + " encountered.");
                    
                    if (token == '!') {
                       eof = true;
                    }
              }
           } while (!eof);
  
        } catch (Exception ex) {
           ex.printStackTrace();
        }
     }
  }
  

  让我们编译并运行以上程序，这将产生以下结果-

   
  Word: AHello.
  Word: AHello.
  Word: This
  Word: This
  Word: is
  Word: is
  Word: a
  Word: a
  Word: text
  Word: text
  Word: that
  Word: that
  Word: will
  Word: will
  Word: be
  Word: be
  Word: split
  Word: split
  Word: into
  Word: into
  Word: tokens.
  Word: tokens.
  Number: 1.0
  Number: 1.0
  + encountered.
  + encountered.
  Number: 1.0
  Number: 1.0
  = encountered.
  = encountered.
  Number: 2.0
  Number: 2.0
  End of File encountered.
  End of File encountered.