在Java/Android中评估包含数学符号的字符串表达式

implementation 'io.apisense:rhino-android:1.1.1'

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import android.util.Log; // 仅适用于Android项目，Java项目可使用System.out.println

public class ExpressionEvaluator {

    private static final String TAG = "ExpressionEvaluator";

    /**
     * 评估一个包含数学符号的字符串表达式。
     *
     * @param expression 待评估的字符串表达式，例如 "5+5", "(10*2)/4", "7.5 + 2.1"
     * @return 表达式的计算结果，以double类型返回
     * @throws UnsupportedOperationException 如果Rhino JavaScript引擎未找到
     * @throws ScriptException 如果表达式评估失败
     * @throws NumberFormatException 如果结果无法转换为double
     */
    public double evaluateMathematicalExpression(String expression) 
            throws UnsupportedOperationException, ScriptException, NumberFormatException {

        Object result = null;
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("rhino");

        if (engine == null) {
            // 如果Rhino引擎未找到，通常意味着依赖未正确配置或环境不支持
            throw new UnsupportedOperationException("JavaScript scripting engine 'rhino' not found. " +
                                                    "Please ensure the Rhino library is correctly added to your project dependencies.");
        }

        try {
            // 使用eval方法评估JavaScript表达式
            result = engine.eval(expression); 
            Log.i(TAG, "Expression: " + expression + ", Raw Result: " + result);

            // 将Object类型的结果转换为double
            // Rhino返回的数值通常是Double类型，但eval()的返回类型是Object
            double val = Double.parseDouble(result.toString());
            Log.i(TAG, "Evaluated Result: " + val);
            return val;

        } catch (ScriptException e) {
            // 捕获脚本执行期间的错误，例如语法错误
            Log.e(TAG, "Error evaluating expression '" + expression + "': " + e.getMessage(), e);
            throw e; // 重新抛出，让调用者处理
        } catch (NumberFormatException e) {
            // 捕获结果转换为double时的错误
            Log.e(TAG, "Error converting result '" + result + "' to double: " + e.getMessage(), e);
            throw e;
        } catch (Exception e) {
            // 捕获其他未知异常
            Log.e(TAG, "An unexpected error occurred: " + e.getMessage(), e);
            throw new RuntimeException("Unexpected error during expression evaluation", e);
        }
    }

    public static void main(String[] args) {
        ExpressionEvaluator evaluator = new ExpressionEvaluator();
        try {
            // 示例用法
            double result1 = evaluator.evaluateMathematicalExpression("5+5"); // 预期 10.0
            System.out.println("Result of '5+5': " + result1);

            double result2 = evaluator.evaluateMathematicalExpression("(10*2)/4 - 1.5"); // 预期 3.5
            System.out.println("Result of '(10*2)/4 - 1.5': " + result2);

            // 尝试一个包含变量的表达式 (Rhino支持，但需注意变量作用域)
            // engine.put("x", 10); // 如果要使用变量，需要先设置
            // double result3 = evaluator.evaluateMathematicalExpression("x * 2");
            // System.out.println("Result of 'x * 2' (x=10): " + result3);

        } catch (UnsupportedOperationException | ScriptException | NumberFormatException e) {
            System.err.println("Evaluation failed: " + e.getMessage());
        }
    }
}