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slgobinathslgobinath
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ANTLR Hello World Calculator
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‎antlr/antlr-demo/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.javahelps.antlr</groupId>
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<artifactId>antlr-demo</artifactId>
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<version>1.0-SNAPSHOT</version>
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<dependencies>
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<dependency>
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<groupId>org.antlr</groupId>
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<artifactId>antlr4-runtime</artifactId>
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<version>4.7.2</version>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<version>3.8.0</version>
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<configuration>
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<source>11</source>
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<target>11</target>
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</configuration>
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</plugin>
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<plugin>
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<groupId>org.antlr</groupId>
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<artifactId>antlr4-maven-plugin</artifactId>
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<version>4.7.2</version>
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<executions>
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<execution>
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<goals>
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<goal>antlr4</goal>
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</goals>
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<configuration>
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<listener>false</listener>
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<visitor>true</visitor>
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</configuration>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

‎antlr/antlr-demo/src/main/antlr4/com/javahelps/antlrdemo/calculator/Calculator.g4‎

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grammar Calculator;
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operation
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: left=NUMBER operator='+' right=NUMBER
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| left=NUMBER operator='-' right=NUMBER
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| left=NUMBER operator='*' right=NUMBER
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| left=NUMBER operator='/' right=NUMBER
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;
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NUMBER
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: ('0' .. '9') + ('.' ('0' .. '9') +)?
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;
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WS : (' ' | '\t')+ -> channel(HIDDEN);

‎antlr/antlr-demo/src/main/java/com/javahelps/antlrdemo/calculator/Calculator.java‎

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package com.javahelps.antlrdemo.calculator;
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import org.antlr.v4.runtime.CharStream;
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import org.antlr.v4.runtime.CharStreams;
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import org.antlr.v4.runtime.CodePointCharStream;
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import org.antlr.v4.runtime.CommonTokenStream;
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import org.antlr.v4.runtime.tree.ParseTree;
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public class Calculator {
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public static void main(String[] args) {
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Calculator calculator = new Calculator();
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System.out.println(calculator.calculate("2 + 5")); // 7.0
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System.out.println(calculator.calculate("2 * 5")); // 10.0
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System.out.println(calculator.calculate("5 - 3")); // 2.0
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System.out.println(calculator.calculate("5 / 3")); // 1.6666666666666667
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System.out.println(calculator.calculate("5 # 3")); // Error: line 1:2 token recognition error at: '#'
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}
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private Double calculate(String source) {
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CodePointCharStream input = CharStreams.fromString(source);
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return compile(input);
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}
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private Double compile(CharStream source) {
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CalculatorLexer lexer = new CalculatorLexer(source);
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CommonTokenStream tokenStream = new CommonTokenStream(lexer);
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CalculatorParser parser = new CalculatorParser(tokenStream);
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ParseTree tree = parser.operation();
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CalculatorVisitorImpl visitor = new CalculatorVisitorImpl();
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return visitor.visit(tree);
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}
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}

‎antlr/antlr-demo/src/main/java/com/javahelps/antlrdemo/calculator/CalculatorVisitorImpl.java‎

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package com.javahelps.antlrdemo.calculator;
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public class CalculatorVisitorImpl extends CalculatorBaseVisitor<Double> {
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@Override
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public Double visitOperation(CalculatorParser.OperationContext ctx) {
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if (ctx.operator == null) {
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throw new UnsupportedOperationException("An operator of +, -, /, * is required to perform the operation");
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}
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String operator = ctx.operator.getText();
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double left = Double.parseDouble(ctx.left.getText());
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double right = Double.parseDouble(ctx.right.getText());
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switch (operator) {
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case "+":
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return left + right;
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case "-":
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return left - right;
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case "/":
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return left / right;
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case "*":
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return left * right;
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default:
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throw new UnsupportedOperationException("Calculator does not support " + operator);
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}
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}
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}

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