void pushBack

描述

所述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，而不是修改在NVAL或SVAL字段的值。

声明

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

public void pushBack()

参数

NA

返回值

此方法不返回值。

异常

NA

实例

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

package com.tutorialspoint;

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();
      }
   }
}

让我们编译并运行上面的程序，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.