Project project = CreateTestProjectWithCustomField();
Task task = project.getRootTask().getChildren().getById(1);

ExtendedAttributeDefinition numberDefinition = ExtendedAttributeDefinition.createTaskDefinition(ExtendedAttributeTask.Number1, null);
project.getExtendedAttributes().add(numberDefinition);

ExtendedAttribute numberAttribute = numberDefinition.createExtendedAttribute();
task.getExtendedAttributes().add(numberAttribute);

// Set ProjDateDiff formula and print extended attribute value
numberDefinition.setFormula("ProjDateDiff(\"03/23/2015\",\"03/18/2015\")");
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());
        
numberDefinition.setFormula("ProjDateDiff(\"03/23/2015\",\"03/25/2015\")");
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());

ExtendedAttributeDefinition dateDefinition = ExtendedAttributeDefinition.createTaskDefinition(ExtendedAttributeTask.Date1, null);
project.getExtendedAttributes().add(dateDefinition);
ExtendedAttribute dateAttribute = dateDefinition.createExtendedAttribute();
task.getExtendedAttributes().add(dateAttribute);

ExtendedAttributeDefinition durationDefinition = ExtendedAttributeDefinition.createTaskDefinition(ExtendedAttributeTask.Duration4, "Custom duration field");
project.getExtendedAttributes().add(durationDefinition);
ExtendedAttribute durationAttribute = durationDefinition.createExtendedAttribute();
task.getExtendedAttributes().add(durationAttribute);

ExtendedAttributeDefinition textDefinition = ExtendedAttributeDefinition.createTaskDefinition(ExtendedAttributeTask.Text5, "Custom text field");
project.getExtendedAttributes().add(textDefinition);
ExtendedAttribute textAttribute = textDefinition.createExtendedAttribute();
task.getExtendedAttributes().add(textAttribute);

// Set ProjDateSub formula and print extended attribute value
dateDefinition.setFormula("ProjDateSub(\"3/19/2015\", \"1d\")");
System.out.println(dateAttribute.getDateValue());

// We can set ProjDurConv formula to duration-valued attribute as well as to text-valued attribute.

// Set ProjDurConv formula to duration-valued extended attribute and print its value.
durationDefinition.setFormula("ProjDurConv([Duration], pjHours)");
System.out.println(durationAttribute.getDurationValue());

// Set ProjDurConv formula to text-valued extended attribute and print its value.
textDefinition.setFormula("ProjDurConv([Duration], pjHours)");
System.out.println(task.getExtendedAttributes().get(0).getTextValue());

textDefinition.setFormula("ProjDurConv([Duration], pjWeeks)");
System.out.println(task.getExtendedAttributes().get(0).getTextValue());

// Set Second formula and print entended attribute value
numberDefinition.setFormula("Second(\"4/21/2015 2:53:41 AM\")");
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());

// Set Weekday formula and print entended attribute value
numberDefinition.setFormula("Weekday(\"24/3/2015\", 1)");
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());
        
numberDefinition.setFormula("Weekday(\"24/3/2015\", 2)");
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());
        
numberDefinition.setFormula("Weekday(\"24/3/2015\", 3)");
System.out.println(task.getExtendedAttributes().get(0).getNumericValue());