antlr4 接触

1. 配置IDE(可选）

2. 加减法示例

编写expr.g4

grammar AddMinus;

expr: Minus Number     #minusNum
     | expr op=('+'|'-') expr #regular
     | Number                     #single
     ;
Number:[0-9]+;
Minus:'-';
WS : [ 	

]+ ->skip ;
Add:'+';

生成文件

实现listener 完成遍历

public static class AddMinusListener extends AddMinusBaseListener{
        private Stack<Integer> stack = new Stack<>();

        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void enterMinusNum(AddMinusParser.MinusNumContext ctx) {
            System.out.println("enter minus: " + ctx.getText());
            System.out.println(ctx);

        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void exitMinusNum(AddMinusParser.MinusNumContext ctx) {
            stack.push(Integer.valueOf(ctx.getText()));
        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void enterRegular(AddMinusParser.RegularContext ctx) {
            System.out.println("enter regular text: " + ctx.getText());
        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void exitRegular(AddMinusParser.RegularContext ctx) {
            if( ctx.op.getText().equals("+")){
                stack.push(stack.pop() + stack.pop());
            }else if( ctx.op.getText().equals("-")){
                Integer peek = stack.pop();
                stack.push(stack.pop() - peek);
            }

            
        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void enterSingle(AddMinusParser.SingleContext ctx) { }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void exitSingle(AddMinusParser.SingleContext ctx) {

            stack.push(Integer.valueOf(ctx.getText()));
        }

        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void enterEveryRule(ParserRuleContext ctx) {

        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void exitEveryRule(ParserRuleContext ctx) {

        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void visitTerminal(TerminalNode node) {


        }
        /**
         * {@inheritDoc}
         *
         * <p>The default implementation does nothing.</p>
         */
        @Override public void visitErrorNode(ErrorNode node) { }

        public Integer getResult(){
            if (stack.size() == 1){
                return stack.peek();
            }
            return 0;
        }
    }

测试代码如下：

        CharStream stream = CharStreams.fromString("2+3-4");
        AddMinusLexer lexer = new AddMinusLexer(stream);
        CommonTokenStream tokenStream = new CommonTokenStream(lexer);
        AddMinusParser parser = new AddMinusParser(tokenStream);
        //parser.setBuildParseTree(true);

        AddMinusParser.ExprContext ctx = parser.expr();
        System.out.println(ctx.toStringTree());
        System.out.println("------------------ up string tree-------");
        ParseTreeWalker walker = new ParseTreeWalker();
        AddMinusListener listener = new AddMinusListener();
        walker.walk(listener,ctx);
        System.out.println(listener.getResult());