在java中解析数学表达式的好库是什么？
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What's a good library for parsing mathematical expressions in java?
提问by CodeFusionMobile
I'm an Android Developer and as part of my next app I will need to evaluate a large variety of user created mathematical expressions and equations. I am looking for a good java library that is lightweight and can evaluate mathematical expressions using user defined variables and constants, trig and exponential functions, etc.
我是一名 Android 开发人员，作为我的下一个应用程序的一部分，我需要评估大量用户创建的数学表达式和方程。我正在寻找一个很好的 Java 库，它是轻量级的，可以使用用户定义的变量和常量、三角函数和指数函数等来评估数学表达式。
I've looked around and Jepseems to be popular, but I would like to hear more suggestions, especially from people who have used these libraries before.
我环顾四周，Jep似乎很受欢迎，但我想听听更多建议，尤其是以前使用过这些库的人的建议。
回答by gpampara
回答by Lawrence Dol
I wrote a simple but capable Math Expression Evaluatora while back, which is free and open-source. It's main advantage is being fast and tiny - both are a good thing with hand-held devices. If it meets your need you are welcome to use it.
不久前，我编写了一个简单但功能强大的Math Expression Evaluator，它是免费且开源的。它的主要优点是快速和小巧 - 两者对于手持设备来说都是一件好事。如果它满足您的需要，欢迎您使用。
Primary Features:
主要特点：
- Basic math operators, with inferred precedence (^ * × · / ÷ % + -).
- Explicit precedence with parenthesis.
- Implicit multiplication of bracketed subexpressions.
- Correct right-associativity of exponentials (power operator).
- Direct support for hexadecimal numbers prefixed by 0x.
- Constants and variables.
- Extensible operators.
- Extensible functions.
- 20 KiB footprint.
- 基本数学运算符，具有推断优先级 (^ * × · / ÷ % + -)。
- 带括号的显式优先级。
- 括号内的子表达式的隐式乘法。
- 修正指数的右结合性（幂运算符）。
- 直接支持以 0x 为前缀的十六进制数字。
- 常量和变量。
- 可扩展的运算符。
- 可扩展的功能。
- 20 KiB 占用空间。
Example
例子
MathEval math=new MathEval();
math.setVariable("Top", 5);
math.setVariable("Left", 20);
math.setVariable("Bottom",15);
math.setVariable("Right", 60);
System.out.println("Middle: "+math.evaluate("floor((Right+1-Left)/2)"));
回答by CodeFusionMobile
This doesn't exactly fit my initial conditions, but I found a wonderful parser written in C++. I'm trying to figure out Android's Native code support to see if I can use it. It's exactly what I need.
这并不完全符合我的初始条件，但我发现了一个用 C++ 编写的很棒的解析器。我正在尝试弄清楚 Android 的本机代码支持，看看我是否可以使用它。这正是我所需要的。
Here's the documentation for the project.
http://www.codeproject.com/KB/recipes/MathieuMathParser.aspx
这是该项目的文档。
http://www.codeproject.com/KB/recipes/MathieuMathParser.aspx
回答by John O
回答by Mohit Gupta
Try https://code.google.com/p/expressionoasis/. It is an extensible Expression Evaluation framework and will meet such requirements.
试试https://code.google.com/p/expressionoasis/。它是一个可扩展的表达式评估框架，将满足此类要求。
