Chapter3 of antlr4----convert initialized Java short arrays to strings(like {1,2,3} to "\u0001\u0002\u0003")

ArrayInit.g4

/** Grammars always start with a grammar header. This grammar is called
 *  ArrayInit and must match the filename: ArrayInit.g4
 */
grammar ArrayInit;

/** A rule called init that matches comma-separated values between {...}. */
init  : '{' value (',' value)* '}' ;  // must match at least one value

/** A value can be either a nested array/struct or a simple integer (INT) */
value : init
      | INT
      ;

// parser rules start with lowercase letters, lexer rules with uppercase
INT :   [0-9]+ ;             // Define token INT as one or more digits
WS  :   [ \t\r\n]+ -> skip ; // Define whitespace rule, toss it out

ShortToUnicodeString.java

/**
 * Created by yingdai on 2017/1/26.
 * In English, the translation is a series of “X goes to Y” rules.
 * 1. Translate { to ".
 * 2. Translate } to ".
 * 3. Translate integers to four-digit hexadecimal strings prefixed with \u.
 */
public class ShortToUnicodeString extends ArrayInitBaseListener{
    public void enterInit(ArrayInitParser.InitContext ctx) {
        System.out.print('"'); }
    /** Translate } to " */
    @Override
    public void exitInit(ArrayInitParser.InitContext ctx) {
        System.out.print('"'); }

    /** Translate integers to 4-digit hexadecimal strings prefixed with \\u */
    @Override
    public void enterValue(ArrayInitParser.ValueContext ctx) {
        // Assumes no nested array initializers
        int value = Integer.valueOf(ctx.INT().getText());
        System.out.printf("\\u%04x", value);
    }
}

Test.java

import org.antlr.v4.runtime.*;

import org.antlr.v4.runtime.tree.*;

public class Test {
        public static void main(String[] args) throws Exception {
            // create a CharStream that reads from standard input
            ANTLRInputStream input = new ANTLRInputStream(System.in); // create a lexer that feeds off of input CharStream
            ArrayInitLexer lexer = new ArrayInitLexer(input); // create a buffer of tokens pulled from the lexer
            CommonTokenStream tokens = new CommonTokenStream(lexer); // create a parser that feeds off the tokens buffer
            ArrayInitParser parser = new ArrayInitParser(tokens);
            ParseTree tree = parser.init(); // begin parsing at init rule
            System.out.println(tree.toStringTree(parser)); // print LISP-style tree }
        }
}
/*
➾ $ javac ArrayInit*.java Test.java
➾ $ java Test
➾ {1,{2,3},4} ➾EOF
❮ (init { (value 1) , (value (init { (value 2) , (value 3) })) , (value 4) })
*/

Translate.java

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;

public class Translate {
    public static void main(String[] args) throws Exception{
        ANTLRInputStream input = new ANTLRInputStream(System.in);
        ArrayInitLexer lexer = new ArrayInitLexer(input);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        ArrayInitParser parser = new ArrayInitParser(tokens);
        ParseTree tree = parser.init();
        ParseTreeWalker walker = new ParseTreeWalker();
        walker.walk(new ShortToUnicodeString(), tree);
        System.out.println();
    }
}

/* commands:
parse tree dialog box:
➾ $ grun ArrayInit init -gui
➾ $ {1,{2,3},4}
➾ $ EOF
================
➾ $ antlr4 ArrayInit.g4 # Generate parser and lexer using antlr4 alias
➾ $ javac ArrayInit*.java Translate.java
➾ $ java Translate
➾ {99, 3, 451} ➾EOF
❮ "\u0063\u0003\u01c3"
*/