MultiKeyMap as O(1) Decision Table

MultiKeyMap excels as an O(1) decision table when using Lists or Maps as key components, enabling instant equality-based lookups across unlimited dimensions with unlimited output parameters.

Equality-Based Matching (Core Strength)

Important: MultiKeyMap performs equality matching on keys (using .equals() and .hashCode()), not relational operations like >, <, >=, or <=. This equality-based approach is what enables O(1) hash table performance.

Best Practice - Hybrid Approach: For decisions requiring both equality matching and relational operations, use MultiKeyMap for the equality-based dimensions and combine with traditional logic for relational criteria:

// Use MultiKeyMap for equality-based criteria (O(1))
MultiKeyMap<Map<String, Object>> equalityRules = new MultiKeyMap<>();
equalityRules.put(baseDecision, "enterprise", "north-america", "credit-card");

// Combine with relational logic for numeric/range criteria
Map<String, Object> decision = equalityRules.get(customerType, region, paymentMethod);
if (decision != null && orderAmount > 10000) {
    decision.put("volumeDiscount", 5.0);  // Add volume-based discount
}
if (decision != null && customerAge < 25) {
    decision.put("youthDiscount", 2.0);   // Add age-based discount  
}

This hybrid approach leverages MultiKeyMap's O(1) performance for categorical/enum-like criteria while handling numeric ranges through efficient conditional logic.

Basic Decision Table Pattern

Business Rules Engine:

// Create decision table with rich structured results
MultiKeyMap<Map<String, Object>> businessRules = new MultiKeyMap<>();

// Define decision dimensions (input criteria)
String customerTier = "enterprise";
String region = "north-america";
String orderVolume = "high";
String paymentMethod = "credit";

// Define rich decision result (multiple outputs)
Map<String, Object> pricingDecision = Map.of(
    "baseDiscount", 15.0,
    "expeditedShipping", true,
    "accountManager", "senior-team",
    "approvalRequired", false,
    "creditTerms", "net-30",
    "volumeBonus", 500.00
);

// Store the decision rule - O(1) insertion
businessRules.put(pricingDecision, customerTier, region, orderVolume, paymentMethod);

// Execute business rule - O(1) lookup, no rule iteration needed!
Map<String, Object> decision = businessRules.get("enterprise", "north-america", "high", "credit");

// Extract multiple decision outputs
double discount = (Double) decision.get("baseDiscount");        // 15.0
boolean expedited = (Boolean) decision.get("expeditedShipping"); // true
String manager = (String) decision.get("accountManager");       // "senior-team"

Decision Table Visualization

The MultiKeyMap acts as a 4-dimensional decision table where each combination of input criteria maps to a rich set of business outputs:

Customer Tier	Region	Order Volume	Payment Method	→ Decision Result
"enterprise"	"north-america"	"high"	"credit"	{baseDiscount: 15.0, expeditedShipping: true, accountManager: "senior-team", approvalRequired: false, creditTerms: "net-30", volumeBonus: 500.00}
"premium"	"europe"	"medium"	"wire"	{baseDiscount: 12.0, expeditedShipping: false, accountManager: "standard-team", approvalRequired: true, creditTerms: "net-15", volumeBonus: 200.00}
"standard"	"asia-pacific"	"low"	"credit"	{baseDiscount: 5.0, expeditedShipping: false, accountManager: "self-service", approvalRequired: true, creditTerms: "prepaid", volumeBonus: 0.00}

Advanced Decision Table with Business Objects

// Decision table with complex business objects as results
MultiKeyMap<Map<String, BusinessObject>> advancedRules = new MultiKeyMap<>();

// Rich business decision with multiple typed objects
Map<String, BusinessObject> dealStructure = Map.of(
    "pricingTier", new PricingTier("enterprise", 15.0, "volume-discount"),
    "servicePlan", new ServicePlan("premium", true, "24x7-support"),
    "accountTeam", new AccountTeam("senior", "john.smith@company.com", "direct-line"),
    "contractTerms", new ContractTerms("annual", "net-30", "auto-renew"),
    "compliance", new ComplianceProfile("sox-compliant", "gdpr-ready", "audit-trail")
);

// Store complex business rule
advancedRules.put(dealStructure, "fortune-500", "financial-services", "multi-year", "enterprise-security");

// Execute complex business decision - still O(1)!
Map<String, BusinessObject> businessDecision = advancedRules.get(
    "fortune-500", "financial-services", "multi-year", "enterprise-security"
);

// Extract strongly-typed business objects
PricingTier pricing = (PricingTier) businessDecision.get("pricingTier");
ServicePlan service = (ServicePlan) businessDecision.get("servicePlan");
AccountTeam team = (AccountTeam) businessDecision.get("accountTeam");
ContractTerms terms = (ContractTerms) businessDecision.get("contractTerms");
ComplianceProfile compliance = (ComplianceProfile) businessDecision.get("compliance");

Type-Safe Decision Table Façade

// Wrap MultiKeyMap in type-safe business interface
public class EnterpriseRulesEngine {
    private final MultiKeyMap<Map<String, BusinessObject>> rules = new MultiKeyMap<>();
    
    public void defineRule(String customerType, String industry, String duration, 
                          String security, Map<String, BusinessObject> decision) {
        rules.put(decision, customerType, industry, duration, security);
    }
    
    public EnterpriseDecision evaluateRule(String customerType, String industry, 
                                         String duration, String security) {
        Map<String, BusinessObject> result = rules.get(customerType, industry, duration, security);
        return result != null ? new EnterpriseDecision(result) : null;
    }
    
    // Type-safe wrapper for decision results
    public static class EnterpriseDecision {
        private final Map<String, BusinessObject> decision;
        
        public EnterpriseDecision(Map<String, BusinessObject> decision) {
            this.decision = decision;
        }
        
        public PricingTier getPricing() { return (PricingTier) decision.get("pricingTier"); }
        public ServicePlan getService() { return (ServicePlan) decision.get("servicePlan"); }
        public AccountTeam getTeam() { return (AccountTeam) decision.get("accountTeam"); }
        public ContractTerms getTerms() { return (ContractTerms) decision.get("contractTerms"); }
        public ComplianceProfile getCompliance() { return (ComplianceProfile) decision.get("compliance"); }
    }
}

Configuration Decision Tables

MultiKeyMap<Properties> configDecisions = new MultiKeyMap<>();

// Environment + Feature + User Role = Configuration Set
List<String> environment = Arrays.asList("prod", "staging");
List<String> features = Arrays.asList("feature-A", "feature-B");
Map<String, String> userAttributes = Map.of("role", "admin", "region", "US");

Properties config = new Properties();
config.setProperty("cache.size", "1000");
config.setProperty("rate.limit", "100");
config.setProperty("debug.enabled", "false");

configDecisions.put(config, environment, features, userAttributes);

// Instant O(1) configuration resolution
Properties resolved = configDecisions.get(
    Arrays.asList("prod", "staging"),
    Arrays.asList("feature-A", "feature-B"),
    Map.of("role", "admin", "region", "US")
);

Decision Table Performance Advantages

• O(1) Rule Execution: Direct hash lookup vs. sequential rule evaluation
• Unlimited Input Dimensions: Scale to any number of decision criteria
• Rich Output Results: Maps/Objects enable unlimited structured decision outputs
• Thread-Safe Decisions: Concurrent rule evaluation for high-throughput systems
• Type-Safe Integration: Façade pattern provides compile-time safety over raw MultiKeyMap

vs. Traditional Rule Engines

Approach	Performance	Flexibility	Memory	Complexity
MultiKeyMap Decision Table	O(1)	Unlimited dimensions	Low	Simple
Traditional Rule Engine	O(n)	Complex pattern matching	High	Complex
IF/ELSE chains	O(n)	Limited scalability	Low	Unmaintainable
Decision Trees	O(log n)	Binary decisions	Medium	Moderate

This pattern transforms MultiKeyMap into a high-performance business rules engine where complex multi-dimensional decisions execute in constant time, regardless of the number of rules stored.

Use Cases

• Pricing Engines: Multi-factor pricing with complex output structures
• Configuration Management: Environment-specific settings with rich metadata
• Access Control: Multi-dimensional permissions with detailed policy results
• Content Routing: Multi-criteria routing with routing metadata
• Business Workflow: State-based decisions with complex next-step information
• Feature Flags: Multi-dimensional feature control with rollout metadata