Jep解析字符串数学公式

如果是一般公式，使用Jep很容易实现计算得到结果。

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String str = "6+7+8-9"; 

Jep jep = new Jep(); 
jep.parse(str); 
System.out.println(jep.evaluate()); 

String str = "6+7+8-9";
Jep jep = new Jep();
jep.parse(str);
System.out.println(jep.evaluate());

默认情况下，Jep支持的符号列表如下：

		Double	Complex	String	Vector
Power	^
Boolean Not	!
Unary Plus, Unary Minus	+x, -x
Dot product, cross product	., ^^
Modulus	%
Division	/
Multiplication	*
Addition, Subtraction	+, -			(only +)
Less or Equal, More or Equal	< =, >=
Less Than, Greater Than	< , >
Not Equal, Equal	!=, ==
Boolean And	&&
Boolean Or	||
Assignment	=

但是一般符号满足不了需求，公式中有比如 x++与a>b?c:d之类的公式，默认的解析明显不支持，想要支持，需要拓展。

支持Java风格公式：

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String str = "3>4?1:2"; 

Jep jep = new Jep(); 
jep.setComponents(new StandardConfigurableParser(),new JavaOperatorTable()); 

jep.parse(str); 
System.out.println(jep.evaluate()); 

String str = "3>4?1:2";
Jep jep = new Jep();
jep.setComponents(new StandardConfigurableParser(),new JavaOperatorTable());
jep.parse(str);
System.out.println(jep.evaluate());

上面代码额外支持的操作符如下：

	Standard symbol	Bitwise OperatorTable	Java OperatorTable	Arguments
Bitwise and	&	[align=center][/align]	[align=center][/align]	Integer
Bitwise or	|	[align=center][/align]	[align=center][/align]	Integer
Bitwise xor	^*	[align=center][/align]	[align=center][/align]	Integer
Bitwise complement	~	[align=center][/align]	[align=center][/align]	Integer
Leftshift	<<	[align=center][/align]	[align=center][/align]	Integer
Signed rightshift	>>	[align=center][/align]	[align=center][/align]	Integer
Unsigned rightshift	>>>	[align=center][/align]	[align=center][/align]	Integer
Pre-increment/decrement	++x, --x	[align=center][/align]	[align=center][/align]	Double variable
Post-increment/decrement	x++, x--	[align=center][/align]	[align=center][/align]	Double variable
Conditional	?:	[align=center][/align]	[align=center][/align]	Double
Assignment	+=, -=, *=, /=, %=	[align=center][/align]	[align=center][/align]	Double
Bitwise assignment	& =, |=, ^=, <<=, >>=, >>>=	[align=center][/align]	[align=center][/align]	Integer

公式里一般不会全是常量，需要对公式里的变量赋值：

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String str = "a>b?1:2"; 

Jep jep = new Jep(); 
jep.setComponents(new StandardConfigurableParser(),new JavaOperatorTable()); 

jep.addVariable("a", 3); 

jep.addVariable("b",
4); 
jep.parse(str); 
System.out.println(jep.evaluate()); 

String str = "a>b?1:2";
Jep jep = new Jep();
jep.setComponents(new StandardConfigurableParser(),new JavaOperatorTable());
jep.addVariable("a", 3);
jep.addVariable("b", 4);
jep.parse(str);
System.out.println(jep.evaluate());

有些字符是保留作为默认值的，不能当做变量：

pi	3.1415... The ratio of the circumference of a circle to its diameter (Math.PI )
e	2.718... Euler's constant in double precision (Math.E)
true	The boolean constant (Boolean.TRUE)
false	The boolean constant (Boolean.FALSE)
i	The complex imaginary unit

Jep还支持自定义公式、使用复杂的数学公式.....。由于上面已经满足项目要求，并且这玩意没源码，方法都要一个个试过去，比较耗时，故而没继续试下去。