Java StreamTokenizer pushBack()用法及代码示例

StreamTokenizer类pushBack()方法

• pushBack() 方法可在java.io包。
• pushBack() 方法用于使此 StreamTokenizer 的下一次调用返回 ttype 字段中的当前值，而不是更新 nval 或 sval 字段值。
• pushBack() 方法是一个非静态方法，它只能通过类对象访问，如果我们尝试使用类名访问方法，那么我们将得到一个错误。
• pushBack() 方法推回时不抛出异常。

用法:

    Public void pushBack();

参数：

• 它不接受任何参数。

返回值：

该方法的返回类型是void，它什么都不返回。

例：

// Java program to demonstrate the example 
// of void pushBack() method of StreamTokenizer

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 {
            // Instantiates FileOutputStream  and ObjectOutputStream 
            FileOutputStream fos_stm = new FileOutputStream("D:\\includehelp.txt");
            ObjectOutputStream obj_out_stm = new ObjectOutputStream(fos_stm);

            // By using writeUTF() method is to
            // write the given string in the file
            obj_out_stm.writeUTF(str);
            obj_out_stm.flush();

            // Instantiates FileOutputStream  and ObjectOutputStream 
            ObjectInputStream obj_in_stm = new ObjectInputStream(new FileInputStream("D:\\includehelp.txt"));

            // Instantiates StreamTokenizer and Reader
            Reader reader = new BufferedReader(new InputStreamReader(obj_in_stm));
            StreamTokenizer st = new StreamTokenizer(reader);

            // Here, we are considering initially 
            // file is not empty
            boolean end_of_file = false;
            do {
                // By using nextToken() method is to
                // parse the next token from the stream
                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.");
                }

                // By using pushBack() method is to
                // push back the last token
                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

@ 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