blocks|key|579494|text|这取决于你想要求值的表达式有多复杂，但对于简单的表达式，java有一个工作得很好的javascript引擎：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|579495|import+javax.script.*;
public+class+EvalScript+{
public+static+void+main(String[]+args)+throws+Exception+{
++++//+create+a+script+engine+manager
++++ScriptEngineManager+factory+=+new+ScriptEngineManager();
++++//+create+a+JavaScript+engine
++++ScriptEngine+engine+=+factory.getEngineByName("JavaScript");
++++//+evaluate+JavaScript+code+from+String
++++Object+obj+=+engine.eval("1%2B2");
++++System.out.println(+obj+);
++++}
}|code-block|syntax|javascript|579496|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

It depends how complex are the expressions you want to eval but for simple ones, java has a javascript engine that works pretty well: 

<pre><code>import javax.script.*;
public class EvalScript {
public static void main(String[] args) throws Exception {
 // create a script engine manager
 ScriptEngineManager factory = new ScriptEngineManager();
 // create a JavaScript engine
 ScriptEngine engine = factory.getEngineByName("JavaScript");
 // evaluate JavaScript code from String
 Object obj = engine.eval("1+2");
 System.out.println( obj );
 }
}
</code></pre>

blocks|key|795575|text|还有一个基于Dijkstra's+Shunting+Yard的表达式求值器exp4j。它可以在Apache+License+2.0下免费获得和重新分发，大小只有大约25KB，并且非常容易使用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|795576|Calculable+calc+=+new+ExpressionBuilder("3+*+sin(y)+-+2+/+(x+-+2)")
++++++++.withVariable("x",+varX)
++++++++.withVariable("y",+varY)
++++++++.build()
double+result1=calc.calculate();|code-block|syntax|javascript|795577|当使用较新的API版本时，如0.4.8|795578|Expression+calc+=+new+ExpressionBuilder("3+*+sin(y)+-+2+/+(x+-+2)")
++++.variable("x",+x)
++++.variable("y",+y)
++++.build();
double+result1+=+calc.evaluate();|795579|还有一个在exp4j中使用定制函数的工具。|795580|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Shunting-yard_algorithm|1|http://projects.congrace.de/exp4j|2^0|6|O|6|O|0|11|5|1|0|0|E|5|0|0|5|5|2|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]|$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1F|8|@]|D|@$9|1G|A|1H|1|1I]]|E|$]]|$1|Q|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]|10|$5|T|U|V|E|$W|Z]]]]

There's also <a href="http://projects.congrace.de/exp4j" rel="noreferrer">exp4j</a>, an expression evaluator based on <a href="https://en.wikipedia.org/wiki/Shunting-yard_algorithm" rel="noreferrer"><code>Dijkstra's Shunting Yard</code></a>. It's freely available and redistributable under the Apache License 2.0, only about 25KB in size, and quite easy to use:

<pre><code>Calculable calc = new ExpressionBuilder("3 * sin(y) - 2 / (x - 2)")
 .withVariable("x", varX)
 .withVariable("y", varY)
 .build()
double result1=calc.calculate();
</code></pre>

When using a newer API version like <code>0.4.8</code>:

<pre><code>Expression calc = new ExpressionBuilder("3 * sin(y) - 2 / (x - 2)")
 .variable("x", x)
 .variable("y", y)
 .build();
double result1 = calc.evaluate();
</code></pre>

There's also a facility to use custom functions in <a href="http://projects.congrace.de/exp4j" rel="noreferrer">exp4j</a>.

blocks|key|579610|text|很好的数学解析器，包含了广泛的数学集合--+mXparser+--请看下面的例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|579611|示例1：|579612|import+org.mariuszgromada.math.mxparser.*;
...
...
Argument+x+=+new+Argument("x+=+pi");
Expression+e+=+new+Expression("sin(x+%2B+pi)/2+%2B+1",+x);
mXparser.consolePrintln("Res+1:+"+%2B+e.getExpressionString()+%2B+"+=+"+%2B+e.calculate());
x.setArgumentValue(2);
mXparser.consolePrintln("Res+2:+"+%2B+e.getExpressionString()+%2B+"+=+"+%2B+e.calculate());|code-block|syntax|javascript|579613|结果：|579614|[mXparser-v.4.0.0]+Res+1:+sin(x+%2B+pi)/2+%2B+1+=+1.0
[mXparser-v.4.0.0]+Res+2:+sin(x+%2B+pi)/2+%2B+1+=+0.545351286587159|579615|示例2：|579616|import+org.mariuszgromada.math.mxparser.*;
...
...
Function+f+=+new+Function("f(x)+=+sin(x+%2B+pi)/2+%2B+1");
Expression+e+=+new+Expression("f(pi)",+f);
mXparser.consolePrintln("Res:+"+%2B+e.getExpressionString()+%2B+"+=+"+%2B+e.calculate());|579617|579618|[mXparser-v.4.0.0]+Res:+f(pi)+=+1.0|579619|为了更好地理解，请关注mXparser+tutorial和mXparser+math+collection。|579620|最近发现-如果您想尝试语法(并查看高级用例)，您可以下载由mXparser提供支持的Scalar+Calculator+app。|579621|诚挚的问候|579622|entityMap|0|LINK|mutability|MUTABLE|url|http://mathparser.org/|1|http://mathparser.org/mxparser-tutorial/|2|http://mathparser.org/mxparser-math-collection/|3|https://scalarmath.org/|4|https://play.google.com/store/apps/details?id=org.mathparser.scalar.lite|5|https://play.google.com/store/apps/details?id=org.mathparser.scalar.pro^0|M|8|0|0|0|0|0|0|0|0|0|0|B|H|1|T|O|2|0|16|6|3|1D|A|4|1O|3|5|0|0^^$0|@$1|2|3|4|5|6|7|1J|8|@]|9|@$A|1K|B|1L|1|1M]]|C|$]]|$1|D|3|E|5|6|7|1N|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|1O|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|1P|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|1Q|8|@]|9|@]|C|$I|J]]|$1|O|3|P|5|6|7|1R|8|@]|9|@]|C|$]]|$1|Q|3|R|5|H|7|1S|8|@]|9|@]|C|$I|J]]|$1|S|3|L|5|6|7|1T|8|@]|9|@]|C|$]]|$1|T|3|U|5|H|7|1U|8|@]|9|@]|C|$I|J]]|$1|V|3|W|5|6|7|1V|8|@]|9|@$A|1W|B|1X|1|1Y]|$A|1Z|B|20|1|21]]|C|$]]|$1|X|3|Y|5|6|7|22|8|@]|9|@$A|23|B|24|1|25]|$A|26|B|27|1|28]|$A|29|B|2A|1|2B]]|C|$]]|$1|Z|3|10|5|6|7|2C|8|@]|9|@]|C|$]]|$1|11|3|-4|5|6|7|2D|8|@]|9|@]|C|$]]]|12|$13|$5|14|15|16|C|$17|18]]|19|$5|14|15|16|C|$17|1A]]|1B|$5|14|15|16|C|$17|1C]]|1D|$5|14|15|16|C|$17|1E]]|1F|$5|14|15|16|C|$17|1G]]|1H|$5|14|15|16|C|$17|1I]]]]

Nice math parser containing broad math collection - <a href="http://mathparser.org/" rel="nofollow noreferrer">mXparser</a> - please see the examples:

Example 1:

<pre><code>import org.mariuszgromada.math.mxparser.*;
...
...
Argument x = new Argument("x = pi");
Expression e = new Expression("sin(x + pi)/2 + 1", x);
mXparser.consolePrintln("Res 1: " + e.getExpressionString() + " = " + e.calculate());
x.setArgumentValue(2);
mXparser.consolePrintln("Res 2: " + e.getExpressionString() + " = " + e.calculate());
</code></pre>

Result:

<pre><code>[mXparser-v.4.0.0] Res 1: sin(x + pi)/2 + 1 = 1.0
[mXparser-v.4.0.0] Res 2: sin(x + pi)/2 + 1 = 0.545351286587159
</code></pre>

Example 2:

<pre><code>import org.mariuszgromada.math.mxparser.*;
...
...
Function f = new Function("f(x) = sin(x + pi)/2 + 1");
Expression e = new Expression("f(pi)", f);
mXparser.consolePrintln("Res: " + e.getExpressionString() + " = " + e.calculate());
</code></pre>

Result:

<pre><code>[mXparser-v.4.0.0] Res: f(pi) = 1.0
</code></pre>

For better understanding please follow <a href="http://mathparser.org/mxparser-tutorial/" rel="nofollow noreferrer">mXparser tutorial</a> and <a href="http://mathparser.org/mxparser-math-collection/" rel="nofollow noreferrer">mXparser math collection</a>.

Found recently - in case you would like to try the syntax (and see the advanced use case) you can download the <a href="https://scalarmath.org" rel="nofollow noreferrer">Scalar</a> <a href="https://play.google.com/store/apps/details?id=org.mathparser.scalar.lite" rel="nofollow noreferrer">Calculator</a> <a href="https://play.google.com/store/apps/details?id=org.mathparser.scalar.pro" rel="nofollow noreferrer">app</a> that is powered by mXparser.

Best regards

blocks|key|579715|text|在列表中添加了另一个选项，我编写了Jep+Java，它作为open+source+project+on+sourceforge获得了很大的人气。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|579716|它支持表达式解析的所有基本常见任务。但是如果你想要定制它，它也增加了很多的可扩展性。许多用户都称赞这个库写得特别好，使用起来也很方便。查看sourceforge评论！|579717|下面是一个包含单个变量的简单示例：|579718|import+com.singularsys.jep.Jep;

Jep+jep+=+new+Jep();
jep.addVariable("x",+10);
jep.parse("x%2B1");
Object+result+=+jep.evaluate();
System.out.println("x+%2B+1+=+"+%2B+result);|code-block|syntax|javascript|579719|这将打印"x+%2B1=+11“。您可以更改变量的值，并再次快速计算表达式。|579720|后来，我还在Singular+Systems+website上提供了一个商业许可的库。|579721|entityMap|0|LINK|mutability|MUTABLE|url|https://sourceforge.net/projects/jep/|1|http://www.singularsys.com/jep^0|T|Y|0|0|0|0|0|0|6|O|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|15|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|16|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]]|C|$]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

Adding another option to the list, I wrote Jep Java which gained a lot of popularity as an <a href="https://sourceforge.net/projects/jep/" rel="nofollow noreferrer">open source project on sourceforge</a>. 

It supports all the basic common tasks of expression parsing. But it also adds a lot of extendibility if you want to customize it. A lot of users have praised the library for being especially well written and easy to use. See the sourceforge reviews!

Here is a simple example with a single variable:

<pre><code>import com.singularsys.jep.Jep;

Jep jep = new Jep();
jep.addVariable("x", 10);
jep.parse("x+1");
Object result = jep.evaluate();
System.out.println("x + 1 = " + result);
</code></pre>

This will print "x + 1 = 11". You can change the value of variables and quickly evaluate the expression again. 

I later also made the library available with a commercial license on the <a href="http://www.singularsys.com/jep" rel="nofollow noreferrer">Singular Systems website</a>.

blocks|key|579780|text|我已经发布了一个类似的答案here。我只想说，我已经开发了一个支持数学、布尔和字符串表达式计算的小型库。下面是一个小示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|579781|String+expression+=+"EXP(var)";
ExpressionEvaluator+evaluator+=+new+ExpressionEvaluator();
evaluator.putVariable(new+Variable("var",+VariableType.NUMBER,+new+BigDecimal(20)));

System.out.println("Value+of+exp(var)+:+"+%2B+evaluator.evaluate(expression).getValue());|code-block|syntax|javascript|579782|如果你感兴趣，可以在here上找到。|579783|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/51162257/3608831|1|https://github.com/Skyost/Algogo/wiki/Algogo-Core#evalute-an-expression^0|D|4|0|0|0|A|4|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

I already have posted a similar answer <a href="https://stackoverflow.com/a/51162257/3608831">here</a>. I just wanted to say that I have been worked on a little library that supports math, boolean and string expression evaluation. Here is a small example :

<pre><code>String expression = "EXP(var)";
ExpressionEvaluator evaluator = new ExpressionEvaluator();
evaluator.putVariable(new Variable("var", VariableType.NUMBER, new BigDecimal(20)));

System.out.println("Value of exp(var) : " + evaluator.evaluate(expression).getValue());
</code></pre>

If you are interested, it is available <a href="https://github.com/Skyost/Algogo/wiki/Algogo-Core#evalute-an-expression" rel="nofollow noreferrer">here</a>.

blocks|key|579903|text|您可以查看ParserNG，这是一个完全成熟且速度极快的数学表达式解析器，它在编译-求值阶段工作。编译阶段解析/理解表达式。评估阶段解决了这个问题，而且速度非常快。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|579904|我称它为解析器，但它不止于此。|579905|它评估数学表达式，支持创建和使用变量和常量，支持内置和创建自定义函数，解决二次方程，联立方程组，塔塔格利亚方程(a.x%5E3%2Bb.x%2Bc=0)，通过迭代方式(使用一些后备技术)解决单个变量中的方程，做基本的统计，微积分(包括它自己的实现，它使用一个符号微分器，它用来吐出给定值的导数的数值)，解决数值积分。|style|CODE|579906|它还通过函数类处理矩阵，并支持使用矩阵函数的各种矩阵运算。|579907|这还不是全部。|579908|作为一个例子，下面是解析器执行一些微积分：|579909|MathExpression+expr+=+new+MathExpression("f(x)=x%5E3*ln(x);+diff(f,3,1)");+
System.out.println("result:+"+%2B+expr.solve());

+result:+38.66253179403897|code-block|syntax|javascript|579910|在this+stackoverflow+answer中查看有关它的更多信息|579911|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/gbenroscience/ParserNG|1|https://stackoverflow.com/questions/2969561/how-to-parse-mathematical-expressions-involving-parentheses/55852113#55852113^0|5|8|0|0|0|1K|D|0|0|0|0|0|1|P|1|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@$A|17|B|18|1|19]]|C|$]]|$1|D|3|E|5|6|7|1A|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|1B|8|@$A|1C|B|1D|H|I]]|9|@]|C|$]]|$1|J|3|K|5|6|7|1E|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|1F|8|@]|9|@]|C|$]]|$1|N|3|O|5|6|7|1G|8|@]|9|@]|C|$]]|$1|P|3|Q|5|R|7|1H|8|@]|9|@]|C|$S|T]]|$1|U|3|V|5|6|7|1I|8|@]|9|@$A|1J|B|1K|1|1L]]|C|$]]|$1|W|3|-4|5|6|7|1M|8|@]|9|@]|C|$]]]|X|$Y|$5|Z|10|11|C|$12|13]]|14|$5|Z|10|11|C|$12|15]]]]

You can check out <a href="https://github.com/gbenroscience/ParserNG" rel="nofollow noreferrer">ParserNG</a>, a full fledged and extremely fast math expression parser which works in compile-evaluate phases.
The compile phase parses/understands the expression. The evaluate phase solves it and is extremely fast.

I called it a parser, but it is more than that. 

It evaluates math expressions, supports creation and usage of variables and constants, supports inbuilt and creation of custom functions, solves quadratic equations, simultaneous equations, Tartaglia's equations(<code>a.x^3+b.x+c=0</code>), solves also equations in a single variable by iterative means(using a number of fallback techniques), does basic statistics, differential calculus(includes its own implementation of a symbolic differentiator which it uses to spit out numerical values for derivatives at given values), solves numerical integrals.

It also handles matrices via a Function class and supports various matrix operations using matrix functions.

And that is not even all.

As an example, here is the parser doing some differential calculus:

<pre><code>MathExpression expr = new MathExpression("f(x)=x^3*ln(x); diff(f,3,1)"); 
System.out.println("result: " + expr.solve());

 result: 38.66253179403897
</code></pre>

See more information about it in <a href="https://stackoverflow.com/questions/2969561/how-to-parse-mathematical-expressions-involving-parentheses/55852113#55852113">this stackoverflow answer</a>

In one of my projects I want to add a feature where the user can provide in a formula, for example

<pre><code>sin (x + pi)/2 + 1
</code></pre>

which I use in my Java app

<pre><code>/**
 * The formula provided by the user
 */
private String formula; // = "sin (x + pi)/2 + 1"

/*
 * Evaluates the formula and computes the result by using the
 * given value for x
 */
public double calc(double x) {
 Formula f = new Formula(formula);
 f.setVar("x", x);
 return f.calc();
 // or something similar
}
</code></pre>

How can I evaluate math expressions?

Method for evaluating math expressions in Java

Java

在我的一个项目中，我想添加一个用户可以在公式中提供的功能，例如sin (x + pi)/2 + 1我在Java应用程序中使用它/** * The formula provided by the user */private String formula; // = "sin (x + pi)/2 + 1"/* * Ev...

问在Java中计算数学表达式的方法
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Java中计算数学表达式的方法EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Java中计算数学表达式的方法
EN