Examples of org.apache.felix.gogo.runtime.Expression

org.apache.felix.gogo.runtime.Expression

rns 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) { {@literal @}Override public BigDecimal eval(List 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)

@author Udo Klimaschewski (http://about.me/udo.klimaschewski)

        variables.put("c", 1l);
        variables.put("d", 2l);
        variables.put("s", " foo ");
        variables.put("t", "bar");


        assertEquals(4l, new Expression("c+=1, d+=2").eval(variables));


        assertEquals(" foo ", new Expression("\" foo \"").eval());
        assertEquals(" foo bar", new Expression("s + t").eval(variables));
        assertEquals(1l, new Expression("s < t").eval(variables));
        assertEquals(1l, new Expression("s > t || t == \"bar\"").eval(variables));


        assertEquals(3l, new Expression("a += 1").eval(variables));
        assertEquals(3l, variables.get("a"));


        assertEquals(30l, new Expression("10 + 20 | 30").eval());


        assertEquals(8l, new Expression("a + b").eval(variables));
        assertEquals(3l, new Expression("if(a < b, a, b)").eval(variables));


        assertEquals(16l, new Expression("2 + 2 << 2").eval());
        assertEquals(8l, new Expression("2 | 2 << 2").eval());
    }

Related Classes of org.apache.felix.gogo.runtime.Expression

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