add threads decrease counter

Author: katrusyavshch

.gitignore

@@ -1,3 +1,4 @@
 .idea/*
 *.iml
 target/*
+

logs/app.log

@@ -0,0 +1,40 @@
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  1, counter value 20
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  1, counter value 19
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 20, counter value 19
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 20, counter value 18
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 19, counter value 18
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 19, counter value 17
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 18, counter value 17
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 18, counter value 16
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 17, counter value 16
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 17, counter value 15
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 16, counter value 15
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 16, counter value 14
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 15, counter value 14
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 15, counter value 13
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 14, counter value 13
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 14, counter value 12
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 13, counter value 12
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 13, counter value 11
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 12, counter value 11
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 12, counter value 10
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 11, counter value 10
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 11, counter value  9
+INFO core.basesyntax.Counter:16  Before decrementing, Thread # 10, counter value  9
+INFO core.basesyntax.Counter:19   After decrementing, Thread # 10, counter value  8
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  9, counter value  8
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  9, counter value  7
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  8, counter value  7
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  8, counter value  6
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  7, counter value  6
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  7, counter value  5
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  6, counter value  5
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  6, counter value  4
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  5, counter value  4
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  5, counter value  3
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  4, counter value  3
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  4, counter value  2
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  3, counter value  2
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  3, counter value  1
+INFO core.basesyntax.Counter:16  Before decrementing, Thread #  2, counter value  1
+INFO core.basesyntax.Counter:19   After decrementing, Thread #  2, counter value  0

src/main/java/core/basesyntax/Counter.java

@@ -6,13 +6,13 @@
 public class Counter {
     private static final Logger logger = LogManager.getLogger(Counter.class);
     private static final String MESSAGE = "%20s, Thread # %2s, counter value %2d";
-    private int value;
+    private volatile int value;
 
     public Counter(int value) {
         this.value = value;
     }
 
-    public void decreaseValue() {
+    public synchronized void decreaseValue() {
         logger.info(String.format(MESSAGE,
                 "Before decrementing", Thread.currentThread().getName(), value));
         value--;