Java的表達式計算引擎 Expr4J

Expr4J 是一個Java的表達式計算引擎，可以用來計算例如在 Excel 單元格中的表達式等。

示例代碼：

package org.boris.expr.util;

import java.io.*;
import org.boris.expr.*;
import org.boris.expr.parser.ExprParser;

public class ExprEvaluator
{
    public static void main(String[] args) throws Exception {
        SimpleEvaluationContext context = new SimpleEvaluationContext();
        System.out.println("Expr Evaluator v1.0");
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        while (true) {
            try {
                System.out.print(">");
                String line = br.readLine();
                if (line == null)
                    break;
                Expr e = ExprParser.parse(line);
                Exprs.toUpperCase(e);
                if (e instanceof ExprEvaluatable) {
                    e = ((ExprEvaluatable) e).evaluate(context);
                }
                System.out.println(e);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

package org.boris.expr.util;

import org.boris.expr.BasicEngineProvider;
import org.boris.expr.engine.DependencyEngine;
import org.boris.expr.engine.Range;

public class DependencyExample
{
    public static void main(String[] args) throws Exception {
        DependencyEngine e = new DependencyEngine(new BasicEngineProvider());
        e.set("B1", "=A1*2");
        e.set("A1", "=12*2");
        e.set("C1", "=B1*A1");
        System.out.println(e.getValue(Range.valueOf("B1")));
        System.out.println(e.getValue(Range.valueOf("C1")));
        e.set("A1", "2");
        System.out.println(e.getValue(Range.valueOf("B1")));
        System.out.println(e.getValue(Range.valueOf("C1")));
    }
}

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