add monitor design pattern (#1640)

* add monitor design pattern .

* add extra line and change compiler version to 11 in pom.xml.

* encapsulate getBalance method .

* update puml file .

* export uml as png .

* duplicate codes eliminated .

* update tag

* change the format of pom.xml

* using logger to print

* change AtomicRefrence to type inference var

* explanations added !

* Update monitor/README.md

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

* Update monitor/README.md

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

* Update monitor/src/main/java/com/iluwatar/monitor/Main.java

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

* Update monitor/src/main/java/com/iluwatar/monitor/Main.java

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

* Update monitor/src/main/java/com/iluwatar/monitor/Main.java

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

* Update monitor/src/main/java/com/iluwatar/monitor/Main.java

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

* e.printStackTrace have changed to logger to prints standard output (STD OUT) .

* add programmatic example .

* Delete mvnw

* mvnw.cmd deleted .

* added mvnw from master

* AddUnitTest

* Add language to readme.md

Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>
Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>
Co-authored-by: Subhrodip Mohanta <subhromo@cisco.com>
Co-authored-by: Subhrodip Mohanta <contact@subho.xyz>

monitor/src/main/java/com/iluwatar/monitor/Bank.java

@@ -0,0 +1,37 @@
+package com.iluwatar.monitor;
+
+import java.util.Arrays;
+import java.util.logging.Logger;
+
+// Bank class implements the Monitor pattern
+public class Bank {
+
+    private int[] accounts;
+    Logger logger;
+
+    public Bank(int accountNum, int baseAmount, Logger logger) {
+        this.logger = logger;
+        accounts = new int[accountNum];
+        Arrays.fill(accounts, baseAmount);
+    }
+
+    public synchronized void transfer(int accountA, int accountB, int amount) {
+        if (accounts[accountA] >= amount) {
+            accounts[accountB] += amount;
+            accounts[accountA] -= amount;
+            logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
+        }
+    }
+
+    public synchronized int getBalance() {
+        int balance = 0;
+        for (int account : accounts) {
+            balance += account;
+        }
+        return balance;
+    }
+
+    public int[] getAccounts() {
+        return accounts;
+    }
+}

monitor/src/main/java/com/iluwatar/monitor/Main.java

@@ -0,0 +1,60 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.monitor;
+
+import java.util.*;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.logging.Logger;
+
+/**
+ * <p>The Monitor pattern is used in concurrent algorithms to achieve mutual exclusion.</p>
+ *
+ * <p>Bank is a simple class that transfers money from an account to another account using
+ * {@link Bank#transfer}. It can also return the balance of the bank account stored in the bank.</p>
+ *
+ * <p>Main class uses ThreadPool to run threads that do transactions on the bank accounts.</p>
+ */
+
+public class Main {
+
+    public static void main(String[] args) {
+        Logger logger = Logger.getLogger("monitor");
+        var bank = new Bank(4, 1000, logger);
+        Runnable runnable = () -> {
+            try {
+                Thread.sleep((long) (Math.random() * 1000));
+                Random random = new Random();
+                for (int i = 0; i < 1000000; i++)
+                    bank.transfer(random.nextInt(4), random.nextInt(4), (int) (Math.random() * 1000));
+            } catch (InterruptedException e) {
+                logger.info(e.getMessage());
+            }
+        };
+        ExecutorService executorService = Executors.newFixedThreadPool(5);
+        for (int i = 0; i < 5; i++) {
+            executorService.execute(runnable);
+        }
+    }
+}

monitor/src/main/test/java/com/iluwater/java/BankTest.java

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+package com.iluwater.java;
+
+import com.iluwatar.monitor.Bank;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assumptions.*;
+
+import java.util.logging.Logger;
+
+public class BankTest {
+
+    private static Bank bank;
+    private static final int ACCOUNT_NUM = 4;
+    private static final int BASE_AMOUNT = 1000;
+    private static final Logger LOGGER = Logger.getLogger("monitor");
+
+    @BeforeAll
+    public static void Setup() {
+        bank = new Bank(ACCOUNT_NUM, BASE_AMOUNT, LOGGER);
+    }
+
+    @Test
+    public void GetAccountHaveNotBeNull() {
+        assertNotNull(bank.getAccounts());
+    }
+
+    @Test
+    public void LengthOfAccountsHaveToEqualsToAccountNumConstant() {
+        assumeTrue(bank.getAccounts() != null);
+        assertEquals(ACCOUNT_NUM, bank.getAccounts().length);
+    }
+
+    @Test
+    public void TransferMethodHaveToTransferAmountFromAnAccountToOtherAccount() {
+        bank.transfer(0, 1, 1000);
+        int accounts[] = bank.getAccounts();
+        assertEquals(0, accounts[0]);
+        assertEquals(2000, 2000);
+    }
+
+    @Test
+    public void BalanceHaveToBeOK() {
+        assertEquals(4000, bank.getBalance());
+    }
+
+
+    @AfterAll
+    public static void TearDown() {
+        bank = null;
+    }
+
+}