RuleBook

gistfile1.txt

RuleBook<String, String> messages = DefaultRuleBook.<String, String>builder()
  .withDefaultResult("?")
  .addRule(rule -> rule.when(code -> code.contains("hello"))
    .then(message -> "Hello World"))
  .addRule(rule -> rule.when(code -> code.contains("goodbye"))
    .then(message -> "Goodbye Cruel World"))
  .build();


RuleBook<Applicant, Double> rates = DefaultRuleBook.<Applicant, Double>builder()
  // default interest rate is 4.5%
  .withDefaultResult(4.5)
  // if they have a credit score below 600 they must pay 4x the default rate and we are done
  .addRule(rule -> rule.when(applicant -> applicant.getCreditScore() < 600)
    .then(rate -> rate * 4)
    .stop())
  // 600-700 pays one point higher
  .addRule(rule -> rule.when(applicant -> applicant.getCreditScore() >= 600 && applicant.getCreditScore() < 700)
    .then(rate -> rate + 1))
  // above 700 + $25k cash on hand gets a 1/4 point reduction
  .addRule(rule -> rule.when(applicant -> applicant.getCreditScore() >= 700 && applicant.getCashOnHand() >= 25000)
    .then(rate -> rate - 0.25))
  // first time home buyers get 20% off of their rate (unless they have a credit score < 600)
  .addRule(rule -> rule.when(applicant -> applicant.isFirstTimeHomeBuyer())
    .then(rate -> rate * 0.80))
  .build();


==================================================================================
Applicant{creditScore=599, cashOnHand=20000.0, firstTimeHomeBuyer=true} -> 18.0% 
Applicant{creditScore=650, cashOnHand=20000.0, firstTimeHomeBuyer=true} -> 4.4% 
Applicant{creditScore=650, cashOnHand=20000.0, firstTimeHomeBuyer=false} -> 5.5% 
Applicant{creditScore=700, cashOnHand=20000.0, firstTimeHomeBuyer=true} -> 3.6% 
Applicant{creditScore=700, cashOnHand=20000.0, firstTimeHomeBuyer=false} -> 4.5% 
Applicant{creditScore=700, cashOnHand=25000.0, firstTimeHomeBuyer=false} -> 4.25% 
Applicant{creditScore=700, cashOnHand=25000.0, firstTimeHomeBuyer=true} -> 3.40% 
==================================================================================