Add chain of responsibility design pattern (#56)

Author: mperor

DesignPatterns/README.md

@@ -9,6 +9,7 @@ with practical examples and best practices for using design patterns to create r
 
 ### Behavioral Design Patterns 💪
 
+- [Chain of Responsibility](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility) 🔗
 - [Command](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command) 📝
 - [Execute Around Method (EAM)](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/eam) ⭕
 - [Observer](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/observer) 👀

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/Banknote.java

@@ -0,0 +1,13 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+enum Banknote {
+    $10,
+    $20,
+    $50,
+    $100,
+    $200;
+
+    int getValue() {
+        return Integer.parseInt(this.name().substring(1));
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/BanknotePocket.java

@@ -0,0 +1,17 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+import java.util.EnumMap;
+import java.util.Map;
+
+class BanknotePocket {
+
+    private final Map<Banknote, Integer> noteToAmount = new EnumMap<>(Banknote.class);
+
+    void add(Banknote note, Integer amount) {
+        noteToAmount.put(note, amount);
+    }
+
+    Integer get(Banknote note) {
+        return noteToAmount.getOrDefault(note, 0);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/Dollar100WithdrawalChain.java

@@ -0,0 +1,8 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+class Dollar100WithdrawalChain extends WithdrawalChain {
+
+    Dollar100WithdrawalChain(int amount) {
+        super(Banknote.$100, amount);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/Dollar10WithdrawalChain.java

@@ -0,0 +1,8 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+class Dollar10WithdrawalChain extends WithdrawalChain {
+
+    Dollar10WithdrawalChain(int amount) {
+        super(Banknote.$10, amount);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/Dollar200WithdrawalChain.java

@@ -0,0 +1,9 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+class Dollar200WithdrawalChain extends WithdrawalChain {
+
+    Dollar200WithdrawalChain(int amount) {
+        super(Banknote.$200, amount);
+    }
+
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/Dollar20WithdrawalChain.java

@@ -0,0 +1,8 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+class Dollar20WithdrawalChain extends WithdrawalChain {
+
+    Dollar20WithdrawalChain(int amount) {
+        super(Banknote.$20, amount);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/Dollar50WithdrawalChain.java

@@ -0,0 +1,8 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+class Dollar50WithdrawalChain extends WithdrawalChain {
+
+    Dollar50WithdrawalChain(int amount) {
+        super(Banknote.$50, amount);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/WithdrawalChain.java

@@ -0,0 +1,36 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+abstract class WithdrawalChain {
+
+    protected final Banknote banknote;
+    protected int banknoteAmount;
+    protected WithdrawalChain nextChain;
+
+    WithdrawalChain(Banknote banknote, int amount) {
+        this.banknote = banknote;
+        this.banknoteAmount = amount;
+    }
+
+    BanknotePocket withdraw(int currency) {
+        int banknoteValue = banknote.getValue();
+        int restValue = currency;
+        int banknoteCounter = 0;
+
+        while (restValue - banknoteValue >= 0 && banknoteAmount > 0) {
+            restValue -= banknoteValue;
+            banknoteCounter++;
+        }
+
+        BanknotePocket pocket = nextChain == null
+                ? new BanknotePocket()
+                : nextChain.withdraw(restValue);
+
+        pocket.add(banknote, banknoteCounter);
+        return pocket;
+    }
+
+    WithdrawalChain next(WithdrawalChain next) {
+        nextChain = next;
+        return next;
+    }
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility/WithdrawalChainTest.java

@@ -0,0 +1,24 @@
+package pl.mperor.lab.java.design.pattern.behavioral.chain.of.responsibility;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class WithdrawalChainTest {
+
+    @Test
+    public void testWithdrawBanknotes() {
+        WithdrawalChain parentChain = new Dollar200WithdrawalChain(2);
+        parentChain.next(new Dollar100WithdrawalChain(2))
+                .next(new Dollar50WithdrawalChain(2))
+                .next(new Dollar20WithdrawalChain(2))
+                .next(new Dollar10WithdrawalChain(2));
+
+        BanknotePocket pocket = parentChain.withdraw(360);
+
+        Assertions.assertEquals(1, pocket.get(Banknote.$200));
+        Assertions.assertEquals(1, pocket.get(Banknote.$100));
+        Assertions.assertEquals(1, pocket.get(Banknote.$50));
+        Assertions.assertEquals(0, pocket.get(Banknote.$20));
+        Assertions.assertEquals(1, pocket.get(Banknote.$10));
+    }
+}