CODEWITHSUNDEEP
javaparsing
user3204065
user3204065

Reputation: 51

java streamTokenizer parser

I have the following grammar:

gui ::=
    Window String widgets
widgets ::=
    Button STRING ';'|
    radio_button End ';'
radio_button ::=
    Radio String ';'

gui, widgets and radio_button are non-terminal. Others are terminal.

The statement I need to parse is:

Window "test" Radio "r1";

I use streamtokenizer in java to do the parsing. When it comes to widgets, I need to test the first line and then the second line. I use nextToken() to get the tokens of the statement. I want to save a copy of the tokenizer before I parse widgets so that if the first line fails, I can use the copy to parse the second line. How to save the copy?

Thanks a lot. I really appreciate your help.

Upvotes: 0

Views: 413

Answers (1)

laune
laune

Reputation: 31300

The StreamTokenizer has a method pushBack which restores the tokenizer's state so that you can call nextToken() again, without skipping the token not matched on the first try.

if( st.nextToken() == st.TT_WORD && "Button".equals( st.sval ){
    // deal with  Button STRING ';'
} else {
    st.pushBack();
    if( radioButton() ){  // call method to recognize Radio String ';'
        // handle End ;
        // ...
    } else {
        // error handling
    }
}


 boolean radioButton(){
     if( st.nextToken() == st.TT_WORD && "Radio".equals( st.sval ){
         // continue to match  String ';'
         // ...
         return true;
     } else {
         st.pushBack();
         return false;
     }
 }

Upvotes: 1

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