Transactions

Author: g1patil

src/main/java/ood/design/Transactions.java

@@ -0,0 +1,102 @@
+package ood.design;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Stack;
+
+public class Transactions {
+
+    private static class Transaction {
+        Map<String, Integer> store;
+        Map<String, Integer> originalStore;
+
+        Transaction(Map<String, Integer> store, Map<String, Integer> originalStore) {
+            this.store = store;
+            this.originalStore = originalStore;
+        }
+    }
+
+    private Map<String, Integer> store = new HashMap<>();
+    private Map<String, Integer> originalStore;
+    private Stack<Transaction> transactions = new Stack<>();
+
+    public void set(String key, int value) {
+        if (!transactions.empty()) {
+            transactions.peek().store.put(key, value);
+        } else {
+            store.put(key, value);
+        }
+    }
+
+    public int get(String key) {
+        if (!transactions.empty()) {
+            Map<String, Integer> transaction = transactions.peek().store;
+            if (transaction.containsKey(key)) {
+                return transaction.get(key);
+            }
+        }
+        return store.get(key);
+    }
+
+    public void delete(String key) {
+        if (!transactions.empty()) {
+            transactions.peek().store.remove(key);
+        } else {
+            store.remove(key);
+        }
+    }
+
+    public void begin() {
+        Map<String, Integer> storeCopy;
+        if(!transactions.isEmpty()){
+            storeCopy = new HashMap<>(transactions.peek().store);
+            transactions.peek().originalStore = new HashMap<>(transactions.peek().store);
+        } else {
+            this.originalStore = new HashMap<>(store);
+            storeCopy = new HashMap<>(store);
+        }
+        transactions.push(new Transaction(new HashMap<>(storeCopy), new HashMap<>(storeCopy)));
+    }
+
+    public void commit() {
+        if (transactions.empty()) {
+            System.out.println("No transaction to commit");
+            return;
+        }
+        Transaction currentTransaction = transactions.pop();
+        if (!transactions.empty()) {
+            transactions.peek().store = currentTransaction.store;
+        } else this.store = currentTransaction.store;
+    }
+
+    public void rollback() {
+        if (transactions.empty()) {
+            this.store = this.originalStore;
+            return;
+        } else {
+            transactions.peek().store = transactions.peek().originalStore;
+        }
+    }
+
+    public static void main(String[] args){
+        Transactions transactions = new Transactions();
+        transactions.set("jivan",1);
+        transactions.set("jivan",2);
+
+        transactions.begin();
+        transactions.set("jivan",3);
+            System.out.println("starting n2");
+            transactions.begin();
+            transactions.set("jivan",4);
+                    transactions.begin();
+                    transactions.set("jivan",5);
+                    transactions.commit();
+                    transactions.rollback();
+            transactions.set("jivan",6);
+            transactions.commit();
+            transactions.rollback();
+        transactions.commit();
+        System.out.println(transactions.get("jivan"));
+
+    }
+}