Project project = CreateTestProjectWithCustomField();
      
// Set arithmetic formula for extended attribute
ExtendedAttributeDefinition attr = project.getExtendedAttributes().get(0);
attr.setAlias("Arithmetic Expression");
attr.setFormula("(1+3*(2+ -5)+8/2)^3");

// Display extended attribute value
Task task = project.getRootTask().getChildren().getById(1);
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());