antlr4 接触

1. 配置IDE(可选）

2. 加减法示例

编写expr.g4

 1 grammar AddMinus;
 2 
 3 expr: Minus Number     #minusNum
 4      | expr op=('+'|'-') expr #regular
 5      | Number                     #single
 6      ;
 7 Number:[0-9]+;
 8 Minus:'-';
 9 WS : [ \t\n\r]+ ->skip ;
10 Add:'+';

生成文件

实现listener 完成遍历

 1 public static class AddMinusListener extends AddMinusBaseListener{
 2         private Stack<Integer> stack = new Stack<>();
 3 
 4         /**
 5          * {@inheritDoc}
 6          *
 7          * <p>The default implementation does nothing.</p>
 8          */
 9         @Override public void enterMinusNum(AddMinusParser.MinusNumContext ctx) {
10             System.out.println("enter minus: " + ctx.getText());
11             System.out.println(ctx);
12 
13         }
14         /**
15          * {@inheritDoc}
16          *
17          * <p>The default implementation does nothing.</p>
18          */
19         @Override public void exitMinusNum(AddMinusParser.MinusNumContext ctx) {
20             stack.push(Integer.valueOf(ctx.getText()));
21         }
22         /**
23          * {@inheritDoc}
24          *
25          * <p>The default implementation does nothing.</p>
26          */
27         @Override public void enterRegular(AddMinusParser.RegularContext ctx) {
28             System.out.println("enter regular text: " + ctx.getText());
29         }
30         /**
31          * {@inheritDoc}
32          *
33          * <p>The default implementation does nothing.</p>
34          */
35         @Override public void exitRegular(AddMinusParser.RegularContext ctx) {
36             if( ctx.op.getText().equals("+")){
37                 stack.push(stack.pop() + stack.pop());
38             }else if( ctx.op.getText().equals("-")){
39                 Integer peek = stack.pop();
40                 stack.push(stack.pop() - peek);
41             }
42 
43             
44         }
45         /**
46          * {@inheritDoc}
47          *
48          * <p>The default implementation does nothing.</p>
49          */
50         @Override public void enterSingle(AddMinusParser.SingleContext ctx) { }
51         /**
52          * {@inheritDoc}
53          *
54          * <p>The default implementation does nothing.</p>
55          */
56         @Override public void exitSingle(AddMinusParser.SingleContext ctx) {
57 
58             stack.push(Integer.valueOf(ctx.getText()));
59         }
60 
61         /**
62          * {@inheritDoc}
63          *
64          * <p>The default implementation does nothing.</p>
65          */
66         @Override public void enterEveryRule(ParserRuleContext ctx) {
67 
68         }
69         /**
70          * {@inheritDoc}
71          *
72          * <p>The default implementation does nothing.</p>
73          */
74         @Override public void exitEveryRule(ParserRuleContext ctx) {
75 
76         }
77         /**
78          * {@inheritDoc}
79          *
80          * <p>The default implementation does nothing.</p>
81          */
82         @Override public void visitTerminal(TerminalNode node) {
83 
84 
85         }
86         /**
87          * {@inheritDoc}
88          *
89          * <p>The default implementation does nothing.</p>
90          */
91         @Override public void visitErrorNode(ErrorNode node) { }
92 
93         public Integer getResult(){
94             if (stack.size() == 1){
95                 return stack.peek();
96             }
97             return 0;
98         }
99     }

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());

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