BAEL-855 stm (#1855)

* BAEL-855 code for the STM article

* BAEL-855 method ordering

* BAEL-855 Better test case

* BAEL-855 formatting

* BAEL-855 rename

* BAEL-855 change to expected

* Merge branch 'master' of https://github.com/eugenp/tutorials into BAEL-855_stm

# Conflicts:
#	libraries/pom.xml

libraries/src/main/java/com/baeldung/stm/Account.java

@@ -0,0 +1,50 @@
+package com.baeldung.stm;
+
+import org.multiverse.api.StmUtils;
+import org.multiverse.api.callables.TxnCallable;
+import org.multiverse.api.references.TxnInteger;
+import org.multiverse.api.references.TxnLong;
+
+public class Account {
+
+    private final TxnLong lastUpdate;
+    private final TxnInteger balance;
+
+    public Account(final int balance) {
+        this.lastUpdate = StmUtils.newTxnLong(System.currentTimeMillis());
+        this.balance = StmUtils.newTxnInteger(balance);
+    }
+
+    public Integer getBalance() {
+        return balance.atomicGet();
+    }
+
+    public void adjustBy(final int amount) {
+        adjustBy(amount, System.currentTimeMillis());
+    }
+
+    public void adjustBy(final int amount, final long date) {
+        StmUtils.atomic(() -> {
+            balance.increment(amount);
+            lastUpdate.set(date);
+
+            if (balance.get() < 0) {
+                throw new IllegalArgumentException("Not enough money");
+            }
+        });
+    }
+
+    public void transferTo(final Account other, final int amount) {
+        StmUtils.atomic(() -> {
+            final long date = System.currentTimeMillis();
+            adjustBy(-amount, date);
+            other.adjustBy(amount, date);
+        });
+    }
+
+    @Override
+    public String toString() {
+        return StmUtils.atomic((TxnCallable<String>)
+                txn -> "Balance: " + balance.get(txn) + " lastUpdateDate: " + lastUpdate.get(txn));
+    }
+}