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