Constants

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It is possible to use global constants in expressions.

Global constants definition

The ConstantsDefinitions singleton class manage a global constants repository shared by all expresssions.

To define a global constant, you just have to add it to the shared global constants repository:

      ConstantsDefinitions globals = ConstantsDefinitions.getInstance();  
      globals.addConstant("myConstant", new Constant(1));        

By default, the type and structure of a constant is set depending on its value^[1] . However, it is possible to specify the type and structure of the constant. For example:

      ConstantsDefinitions globals = ConstantsDefinitions.getInstance();  
      globals.addConstant("myConstant", new Constant(1, ExpressionType.TYPE_FLOAT));        

Note that as for variables, global constants are shared by all expressions.

Usage

When encountering the constant name, an expression will use the value of the constant. For example:

      ConstantsDefinitions globals = ConstantsDefinitions.getInstance();  
      globals.addConstant("myConstant", new Constant(1));     
        
      Equation equation = ExpressionJ.parse("myConstant+2");   
      Objet value =  equation.eval();   

The result of value will be 3.

Local constants

It is possible to define constants local to a code block. For example:

      Equation equation = ExpressionJ.parse("const a = 2; return a + 1");  
      Object result = equation.eval();   
      // the result is 3       

Notes

See Also

• Local constants: This article explains the notion of variables in expressions

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Categories: concepts