Showing how to avoid exposing common package private interface in an …

…API with the help of an internal class Evaluator which encapsulates all the polymorphic calls into various bets.

src/cz/kamosh/betExample/BettingAgency.java

@@ -21,22 +21,38 @@ public double getCurrentCashAmount() {
     }
 
     public double evaluateBet(double amount, DrawableBetResult expectedResult, DrawableRandomBet checkDrawableBet) {
-        return innerEvaluateBet(amount, expectedResult, checkDrawableBet);
+        class EvalDrawableBet extends Evaluate<DrawableRandomBet> {
+            @Override
+            protected InnerBetResult betResult(DrawableRandomBet b) {
+                return b.checkBet().getInnerBetResult();
+            }
+        }
+        return new EvalDrawableBet().innerEvaluateBet(amount, expectedResult, checkDrawableBet);
     }
 
     public double evaluateBet(double amount, WinLostBetResult expectedResult, WinLostTimeBasedBet checkWinLooseBet) {
-        return innerEvaluateBet(amount, expectedResult, checkWinLooseBet);
-    }
-
-    private double innerEvaluateBet(double amount, BetResult betResult, Bet checkBet) {
-        if(amount < 0) {
-            throw new IllegalArgumentException("Cannot bet negative money");
+        class EvalWinLostBet extends Evaluate<WinLostTimeBasedBet> {
+            @Override
+            protected InnerBetResult betResult(WinLostTimeBasedBet b) {
+                return b.checkBet().getInnerBetResult();
+            }
         }
-        cash += amount;
-        if (checkBet.checkBet().getInnerBetResult() == betResult.getInnerBetResult()) {
-            cash -= amount * BETTING_ODD;
-            return amount * BETTING_ODD; // User won
+        return new EvalWinLostBet().innerEvaluateBet(amount, expectedResult, checkWinLooseBet);
+    }
+
+    private abstract class Evaluate<BET> {
+        public double innerEvaluateBet(double amount, BetResult betResult, BET checkBet) {
+            if(amount < 0) {
+                throw new IllegalArgumentException("Cannot bet negative money");
+            }
+            cash += amount;
+            if (betResult(checkBet) == betResult.getInnerBetResult()) {
+                cash -= amount * BETTING_ODD;
+                return amount * BETTING_ODD; // User won
+            }
+            return 0;
         }
-        return 0;
+
+        protected abstract InnerBetResult betResult(BET b);
     }
 }

src/cz/kamosh/betExample/DrawableBet.java

@@ -3,9 +3,8 @@
 /**
  * You may introduce a new  type of drawable bet by implementing this interface.
  */
-public interface DrawableBet extends Bet<DrawableBetResult> {
+public interface DrawableBet {
 
-    @Override
     public DrawableBetResult checkBet();
 
 }

src/cz/kamosh/betExample/DrawableRandomBet.java

@@ -5,10 +5,9 @@
 /**
  * This is basic implementation of drawable bet based on random numbers.
  */
-public final class DrawableRandomBet implements Bet<DrawableBetResult> {    
+public final class DrawableRandomBet  {    
     private static Random rnd = new Random(System.currentTimeMillis());
 
-    @Override
     public DrawableBetResult checkBet() {
         switch(rnd.nextInt(3)) {
             case 0:

src/cz/kamosh/betExample/WinLostBet.java

@@ -3,9 +3,8 @@
 /**
  * You may introduce a new type of win/lost bet by implementing this interface.
  */
-public interface WinLostBet extends Bet<WinLostBetResult>{
+public interface WinLostBet {
 
-    @Override
     public WinLostBetResult checkBet();
 
 }

src/cz/kamosh/betExample/WinLostTimeBasedBet.java

@@ -3,9 +3,8 @@
 /** 
  * This is basic implementation of win/lost bet based on current time.
  */
-public final class WinLostTimeBasedBet implements Bet<WinLostBetResult> {    
+public final class WinLostTimeBasedBet {    
 
-    @Override
     public WinLostBetResult checkBet() {
         if(System.currentTimeMillis() % 2 == 0) {
             return WinLostBetResult.WIN;