string as boolean

Question

I'm making a spreadsheet in Java.

I'd like to make a copy of the Microsoft Excel function ISLOGICAL. It checks whether a value is a logical value (TRUE or FALSE), and returns TRUE or FALSE.

All cells are arrays of string. This is what I have now:

public static String islogical(String[] value){
        String err = "#ERROR!";
        if (value.length != 1){
            return err;
        }

        boolean a = false;

        try{
            a = Boolean.parseBoolean(value[0]);
        }
        catch(IllegalArgumentException e){return err;}

        String ans = "FALSE";

        if(a){
            ans = "TRUE";
            return ans;
        }
        else{
            return ans;
        }

    }

I don't understand why, if my string value = "8>3", that it doesn't give me back true. All inputs, except the string = true, gives back false.

Java does not have a built in expression evaluation mechanism, it sounds like you'll need to write a Domain Specific Language. — Elliott Frisch, Jan 16 '14 at 21:09
Look here http://stackoverflow.com/questions/1762878/how-to-check-if-string-value-is-boolean-type-in-java — marek.kapowicki, Jan 16 '14 at 21:12

score 1 · Answer 1 · edited Jun 20 '20 at 09:12

I don't understand why, if my 'string value = "8>3"', that it doesn't give me back 'true'

That happens because parseBoolean() does not evaluate expressions.

From the Javadoc:

Parses the string argument as a boolean. The boolean returned represents the value true if the string argument is not null and is equal, ignoring case, to the string "true".

Example: Boolean.parseBoolean("True") returns true.

Example: Boolean.parseBoolean("yes") returns false.

score 1 · Answer 2 · answered Jan 16 '14 at 21:10

Boolean.parseBoolean() will return the boolean representation of a string. So "True" returns true, every thign else returns false.

What you want is to evaluate the string - check out https://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

public static String islogical(String[] value){
    String err = "#ERROR!";
    if (value.length != 1){
        return err;
    }

    boolean a = false;

    try{
        a = engine.eval(value[0]);
    }
    catch(IllegalArgumentException e){return err;}

    String ans = "FALSE";

    if(a){
        ans = "TRUE";
        return ans;
    }
    else{
        return ans;
    }

}

score 0 · Answer 3 · edited May 23 '17 at 10:25

0

Have you tried using the eval method? Here's an example from Is there an eval() function in Java?:

    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("js");        
    Object result = engine.eval("3+4");

edited May 23 '17 at 10:25

Community

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answered Jan 16 '14 at 21:13

user3204117

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Alexey Lebedev · Answer 4 · 2014-01-18T12:34:32.523

The parameters for function evaluation must have simple data types, like numbers, booleans, strings, etc. All subexpressions must be calculated before you make a call for your function.

The expression “=ISLOGICAL(8>3)” must be evaluated in the following order:

Calculation of “8>3” subexpression. The result is a boolean value TRUE. The expression now looks like =ISLOGICAL(TRUE);
Function ISLOGICAL evaluation on the TRUE argument. The result is TRUE.

If your expression is =ISLOGICAL(“8>3”) then your function correctly returns FALSE, because the "8>3” has string data type, not boolean. The best way for evaluation of excel-like expressions is the use of reverse-polish notation. Please follow wiki for details.

string as boolean

4 Answers4