Java StreamTokenizer pushBack()方法与示例

StreamTokenizer类pushBack()方法

  • pushBack()方法在java.io包中可用。

  • pushBack()方法用于使该StreamTokenizer的下一次调用返回ttype字段中的当前值,而不更新nval或sval字段值。

  • pushBack()方法是一种非静态方法,只能通过类对象访问,如果尝试使用类名称访问该方法,则会收到错误消息。

  • pushBack()方法在推回时不会引发异常。

语法:

    Public void pushBack();

参数:

  • 它不接受任何参数。

返回值:

该方法的返回类型为void,不返回任何内容。

示例

// Java程序演示示例 
// pushBack()StreamTokenizer的void方法

import java.io.*;

public class PushBack {
    public static void main(String[] args) {
        String str = "Hi, This is \n a mathematical expression :\n " +
            " 2 * 4 = 8 " + "8 + 5 = 13";

        try {
            //实例化FileOutputStream和ObjectOutputStream- 
            FileOutputStream fos_stm = new FileOutputStream("D:\\includehelp.txt");
            ObjectOutputStream obj_out_stm = new ObjectOutputStream(fos_stm);

            //通过使用writeUTF()方法是
            //将给定的字符串写入文件
            obj_out_stm.writeUTF(str);
            obj_out_stm.flush();

            //实例化FileOutputStream和ObjectOutputStream- 
            ObjectInputStream obj_in_stm = new ObjectInputStream(new FileInputStream("D:\\includehelp.txt"));

            //实例化StreamTokenizer和Reader-
            Reader reader = new BufferedReader(new InputStreamReader(obj_in_stm));
            StreamTokenizer st = new StreamTokenizer(reader);

            //在这里,我们开始考虑 
            //文件不为空
            boolean end_of_file = false;
            do {
                //通过使用nextToken()方法是
                //解析流中的下一个标记
                int token = st.nextToken();

                switch (token) {

                    case StreamTokenizer.TT_EOF:
                        System.out.println("End of File Found");
                        end_of_file = true;
                        break;

                    case StreamTokenizer.TT_EOL:
                        System.out.println("End of Line Found");
                        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 + " Found.");
                }

                //通过使用pushBack()方法是
                //返回最后一个令牌
                st.pushBack();
                token = st.nextToken();

                switch (token) {
                    case StreamTokenizer.TT_EOF:
                        System.out.println("End of File Found");
                        end_of_file = true;
                        break;

                    case StreamTokenizer.TT_EOL:
                        System.out.println("End of Line Found");
                        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 + " Found.");
                }
            } while (!end_of_file);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

输出结果

@ Found.
@ Found.
word: Hi
word: Hi
, Found.
, Found.
word: This
word: This
word: is
word: is
word: a
word: a
word: mathematical
word: mathematical
word: expression
word: expression
: Found.
: Found.
number: 2.0
number: 2.0
* Found.
* Found.
number: 4.0
number: 4.0
= Found.
= Found.
number: 8.0
number: 8.0
number: 8.0
number: 8.0
+ Found.
+ Found.
number: 5.0
number: 5.0
= Found.
= Found.
number: 13.0
number: 13.0
End of File Found
End of File Found