Example of expression evaluation

This is a quite simple expression evaluator of additions and multiplications using JSqlParser. The ExpressionDeParser is used to traverse and interpret the parse tree.

import java.util.Stack;
import net.sf.jsqlparser.JSQLParserException;
import net.sf.jsqlparser.expression.Expression;
import net.sf.jsqlparser.expression.LongValue;
import net.sf.jsqlparser.expression.operators.arithmetic.Addition;
import net.sf.jsqlparser.expression.operators.arithmetic.Multiplication;
import net.sf.jsqlparser.parser.CCJSqlParserUtil;
import net.sf.jsqlparser.util.deparser.ExpressionDeParser;

public class SimpleEvaluateExpr {
    
    public static void main( String[] args ) throws JSQLParserException {
	evaluate("4+5*6");
	evaluate("4*5+6");
	evaluate("4*(5+6)");
	evaluate("4*(5+6)*(2+3)");
    }

    static void evaluate(String expr) throws JSQLParserException {
	final Stack<Long> stack = new Stack<Long>();
	System.out.println("expr=" + expr);
	Expression parseExpression = CCJSqlParserUtil.parseExpression(expr);
	ExpressionDeParser deparser = new ExpressionDeParser() {
	    @Override
	    public void visit(Addition addition) {
		super.visit(addition); 
		
		long sum1 = stack.pop();
		long sum2 = stack.pop();
		
		stack.push(sum1 + sum2);
	    }

	    @Override
	    public void visit(Multiplication multiplication) {
		super.visit(multiplication); 
		
		long fac1 = stack.pop();
		long fac2 = stack.pop();
		
		stack.push(fac1 * fac2);
	    }

	    @Override
	    public void visit(LongValue longValue) {
		super.visit(longValue); 
		stack.push(longValue.getValue());
	    }
	};
	StringBuilder b = new StringBuilder();
	deparser.setBuffer(b);
	parseExpression.accept(deparser);
	
	System.out.println(expr + " = " + stack.pop() );
    }
}

And this is the result output:

expr=4+5*6
4+5*6 = 34
expr=4*5+6
4*5+6 = 26
expr=4*(5+6)
4*(5+6) = 44
expr=4*(5+6)*(2+3)
4*(5+6)*(2+3) = 220