Package org.apache.felix.gogo.runtime

Class Expression

  • public class Expression
extends java.lang.Object

    EvalEx - Java Expression Evaluator

    Introduction

    EvalEx is a handy expression evaluator for Java, that allows to evaluate simple mathematical and boolean expressions.
    Key Features:
    • Uses BigDecimal for calculation and result
    • Single class implementation, very compact
    • No dependencies to external libraries
    • Precision and rounding mode can be set
    • Supports variables
    • Standard boolean and mathematical operators
    • Standard basic mathematical and boolean functions
    • Custom functions and operators can be added at runtime

    Examples

      BigDecimal result = null;

  Expression expression = new Expression("1+1/3");
  result = expression.eval():
  expression.setPrecision(2);
  result = expression.eval():

  result = new Expression("(3.4 + -4.1)/2").eval();

  result = new Expression("SQRT(a^2 + b^2").with("a","2.4").and("b","9.253").eval();

  BigDecimal a = new BigDecimal("2.4");
  BigDecimal b = new BigDecimal("9.235");
  result = new Expression("SQRT(a^2 + b^2").with("a",a).and("b",b).eval();

  result = new Expression("2.4/PI").setPrecision(128).setRoundingMode(RoundingMode.UP).eval();

  result = new Expression("random() > 0.5").eval();

  result = new Expression("not(x < 7 || sqrt(max(x,9)) <= 3))").with("x","22.9").eval();

    Supported Operators

    Mathematical Operators
    OperatorDescription
    +Additive operator
    -Subtraction operator
    *Multiplication operator
    /Division operator
    %Remainder operator (Modulo)
    ^Power operator

    Boolean Operators*
    OperatorDescription
    =Equals
    ==Equals
    !=Not equals
    <>Not equals
    <Less than
    <=Less than or equal to
    >Greater than
    >=Greater than or equal to
    &&Boolean and
    ||Boolean or
    *Boolean operators result always in a BigDecimal value of 1 or 0 (zero). Any non-zero value is treated as a _true_ value. Boolean _not_ is implemented by a function.

    Supported Functions

    Function*Description
    NOT(expression)Boolean negation, 1 (means true) if the expression is not zero
    IF(condition,value_if_true,value_if_false)Returns one value if the condition evaluates to true or the other if it evaluates to false
    RANDOM()Produces a random number between 0 and 1
    MIN(e1,e2)Returns the smaller of both expressions
    MAX(e1,e2)Returns the bigger of both expressions
    ABS(expression)Returns the absolute (non-negative) value of the expression
    ROUND(expression,precision)Rounds a value to a certain number of digits, uses the current rounding mode
    FLOOR(expression)Rounds the value down to the nearest integer
    CEILING(expression)Rounds the value up to the nearest integer
    LOG(expression)Returns the natural logarithm (base e) of an expression
    SQRT(expression)Returns the square root of an expression
    SIN(expression)Returns the trigonometric sine of an angle (in degrees)
    COS(expression)Returns the trigonometric cosine of an angle (in degrees)
    TAN(expression)Returns the trigonometric tangens of an angle (in degrees)
    SINH(expression)Returns the hyperbolic sine of a value
    COSH(expression)Returns the hyperbolic cosine of a value
    TANH(expression)Returns the hyperbolic tangens of a value
    RAD(expression)Converts an angle measured in degrees to an approximately equivalent angle measured in radians
    DEG(expression)Converts an angle measured in radians to an approximately equivalent angle measured in degrees
    *Functions names are case insensitive.

    Supported Constants

    ConstantDescription
    PIThe value of PI, exact to 100 digits
    TRUEThe value one
    FALSEThe value zero

    Add Custom Operators

    Custom operators can be added easily, simply create an instance of `Expression.Operator` and add it to the expression. Parameters are the operator string, its precedence and if it is left associative. The operators `eval()` method will be called with the BigDecimal values of the operands. All existing operators can also be overridden.
    For example, add an operator `x >> n`, that moves the decimal point of _x_ _n_ digits to the right: 
     Expression e = new Expression("2.1234 >> 2");

 e.addOperator(e.new Operator(">>", 30, true) {
     @Override
     public BigDecimal eval(BigDecimal v1, BigDecimal v2) {
         return v1.movePointRight(v2.toBigInteger().intValue());
     }
 });

 e.eval(); // returns 212.34

    Add Custom Functions

    Adding custom functions is as easy as adding custom operators. Create an instance of `Expression.Function`and add it to the expression. Parameters are the function name and the count of required parameters. The functions `eval()` method will be called with a list of the BigDecimal parameters. All existing functions can also be overridden.
    For example, add a function `average(a,b,c)`, that will calculate the average value of a, b and c: 
     Expression e = new Expression("2 * average(12,4,8)");

 e.addFunction(e.new Function("average", 3) {
     @Override
     public BigDecimal eval(List<BigDecimal> parameters) {
         BigDecimal sum = parameters.get(0).add(parameters.get(1)).add(parameters.get(2));
         return sum.divide(new BigDecimal(3));
     }
 });

 e.eval(); // returns 16
    The software is licensed under the MIT Open Source license (see LICENSE file).
    • The *power of* operator (^) implementation was copied from [Stack Overflow](http://stackoverflow.com/questions/3579779/how-to-do-a-fractional-power-on-bigdecimal-in-java) Thanks to Gene Marin
    • The SQRT() function implementation was taken from the book [The Java Programmers Guide To numerical Computing](http://www.amazon.de/Java-Number-Cruncher-Programmers-Numerical/dp/0130460419) (Ronald Mak, 2002)

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private java.util.Map<java.lang.String,​java.lang.Object> constants
      All defined variables with name and value.
      private char decimalSeparator
      What character to use for decimal separators.
      private java.lang.String expression
      The original infix expression.
      private java.util.Map<java.lang.String,​Expression.Function> functions
      All defined functions with name and implementation.
      private java.math.MathContext mc
      The MathContext to use for calculations.
      private char minusSign
      What character to use for minus sign (negative values).
      private java.util.Map<java.lang.String,​Expression.Operator> operators
      All defined operators with name and implementation.
      static java.math.BigDecimal PI
      Definition of PI as a constant, can be used in expressions as variable.
      private java.util.List<Expression.Token> rpn
      The cached RPN (Reverse Polish Notation) of the expression.

    • Constructor Summary

      Constructors 
      Constructor Description
      Expression​(java.lang.String expression)
      Creates a new expression instance from an expression string.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      Expression addConstant​(java.lang.String name, java.lang.Object value)
      Sets a constant value.
      Expression.Function addFunction​(Expression.Function function)
      Adds a function to the list of supported functions
      Expression.Operator addOperator​(Expression.Operator operator)
      Adds an operator to the list of supported operators.
      java.lang.Object eval()
      Evaluates the expression.
      java.lang.Object eval​(java.util.Map<java.lang.String,​java.lang.Object> variables)
      Evaluates the expression.
      java.util.Iterator<java.lang.String> getExpressionTokenizer()
      Get an iterator for this expression, allows iterating over an expression token by token.
      private java.util.List<Expression.Token> getRPN()
      Cached access to the RPN notation of this expression, ensures only one calculation of the RPN per expression instance.
      private boolean isNumber​(java.lang.Object obj)  
      private boolean isNumber​(java.lang.String st)
      Is the string a number?
      Expression setPrecision​(int precision)
      Sets the precision for expression evaluation.
      Expression setRoundingMode​(java.math.RoundingMode roundingMode)
      Sets the rounding mode for expression evaluation.
      private java.util.List<Expression.Token> shuntingYard​(java.lang.String expression)
      Implementation of the Shunting Yard algorithm to transform an infix expression to a RPN expression.
      private java.math.BigDecimal toBigDecimal​(java.lang.Object o)  
      private java.math.BigDecimal toBigDecimal​(java.util.Map<java.lang.String,​java.lang.Object> variables, java.lang.Object o)  
      private java.lang.Number toResult​(java.math.BigDecimal r)  
      java.lang.String toRPN()
      Get a string representation of the RPN (Reverse Polish Notation) for this expression.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • PI

        public static final java.math.BigDecimal PI
        Definition of PI as a constant, can be used in expressions as variable.

      • mc

        private java.math.MathContext mc
        The MathContext to use for calculations.

      • expression

        private java.lang.String expression
        The original infix expression.

      • rpn

        private java.util.List<Expression.Token> rpn
        The cached RPN (Reverse Polish Notation) of the expression.

      • operators

        private java.util.Map<java.lang.String,​Expression.Operator> operators
        All defined operators with name and implementation.

      • functions

        private java.util.Map<java.lang.String,​Expression.Function> functions
        All defined functions with name and implementation.

      • constants

        private java.util.Map<java.lang.String,​java.lang.Object> constants
        All defined variables with name and value.

      • decimalSeparator

        private final char decimalSeparator
        What character to use for decimal separators.
        See Also:
        Constant Field Values

      • minusSign

        private final char minusSign
        What character to use for minus sign (negative values).
        See Also:
        Constant Field Values

    • Constructor Detail

      • Expression

        public Expression​(java.lang.String expression)
        Creates a new expression instance from an expression string.
        Parameters:
        expression - The expression. E.g. "2.4*sin(3)/(2-4)" or "sin(y)>0 & max(z, 3)>3"

    • Method Detail

      • isNumber

        private boolean isNumber​(java.lang.String st)
        Is the string a number?
        Parameters:
        st - The string.
        Returns:
        true, if the input string is a number.

      • isNumber

        private boolean isNumber​(java.lang.Object obj)

      • shuntingYard

        private java.util.List<Expression.Token> shuntingYard​(java.lang.String expression)
        Implementation of the Shunting Yard algorithm to transform an infix expression to a RPN expression.
        Parameters:
        expression - The input expression in infx.
        Returns:
        A RPN representation of the expression, with each token as a list member.

      • eval

        public java.lang.Object eval()
        Evaluates the expression.
        Returns:
        The result of the expression.

      • eval

        public java.lang.Object eval​(java.util.Map<java.lang.String,​java.lang.Object> variables)
        Evaluates the expression.
        Parameters:
        variables - the variables
        Returns:
        The result of the expression.

      • toResult

        private java.lang.Number toResult​(java.math.BigDecimal r)

      • toBigDecimal

        private java.math.BigDecimal toBigDecimal​(java.util.Map<java.lang.String,​java.lang.Object> variables,
                                          java.lang.Object o)

      • toBigDecimal

        private java.math.BigDecimal toBigDecimal​(java.lang.Object o)

      • setPrecision

        public Expression setPrecision​(int precision)
        Sets the precision for expression evaluation.
        Parameters:
        precision - The new precision.
        Returns:
        The expression, allows to chain methods.

      • setRoundingMode

        public Expression setRoundingMode​(java.math.RoundingMode roundingMode)
        Sets the rounding mode for expression evaluation.
        Parameters:
        roundingMode - The new rounding mode.
        Returns:
        The expression, allows to chain methods.

      • addOperator

        public Expression.Operator addOperator​(Expression.Operator operator)
        Adds an operator to the list of supported operators.
        Parameters:
        operator - The operator to add.
        Returns:
        The previous operator with that name, or null if there was none.

      • addFunction

        public Expression.Function addFunction​(Expression.Function function)
        Adds a function to the list of supported functions
        Parameters:
        function - The function to add.
        Returns:
        The previous operator with that name, or null if there was none.

      • addConstant

        public Expression addConstant​(java.lang.String name,
                              java.lang.Object value)
        Sets a constant value.
        Parameters:
        name - The constant name.
        value - The constant value.
        Returns:
        The expression, allows to chain methods.

      • getExpressionTokenizer

        public java.util.Iterator<java.lang.String> getExpressionTokenizer()
        Get an iterator for this expression, allows iterating over an expression token by token.
        Returns:
        A new iterator instance for this expression.

      • getRPN

        private java.util.List<Expression.Token> getRPN()
        Cached access to the RPN notation of this expression, ensures only one calculation of the RPN per expression instance. If no cached instance exists, a new one will be created and put to the cache.
        Returns:
        The cached RPN instance.

      • toRPN

        public java.lang.String toRPN()
        Get a string representation of the RPN (Reverse Polish Notation) for this expression.
        Returns:
        A string with the RPN representation for this expression.