diff --git a/hw-04/.gitignore b/hw-04/.gitignore
new file mode 100644
index 0000000..6a6df0f
--- /dev/null
+++ b/hw-04/.gitignore
@@ -0,0 +1,61 @@
+# Emacs/vim
+
+*~
+*.swp
+
+# VSCode
+
+.vscode
+.classpath
+.project
+.settings/
+
+
+# MacOS
+
+.DS_Store
+
+# CS56 specific: Secrets files
+
+localhost.json
+heroku.json
+
+# Maven (from: https://github.com/github/gitignore/blob/master/Maven.gitignore)
+
+target/
+pom.xml.tag
+pom.xml.releaseBackup
+pom.xml.versionsBackup
+pom.xml.next
+release.properties
+dependency-reduced-pom.xml
+buildNumber.properties
+.mvn/timing.properties
+# https://github.com/takari/maven-wrapper#usage-without-binary-jar
+.mvn/wrapper/maven-wrapper.jar
+
+# Java (from: https://github.com/github/gitignore/blob/master/Java.gitignore)
+
+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
diff --git a/hw-04/artifacts/result.pdf b/hw-04/artifacts/result.pdf
new file mode 100644
index 0000000..bdb9ea7
Binary files /dev/null and b/hw-04/artifacts/result.pdf differ
diff --git a/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-42-20.png b/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-42-20.png
new file mode 100644
index 0000000..f0ed90c
Binary files /dev/null and b/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-42-20.png differ
diff --git a/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-43-01.png b/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-43-01.png
new file mode 100644
index 0000000..75d361b
Binary files /dev/null and b/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-43-01.png differ
diff --git a/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-51-48.png b/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-51-48.png
new file mode 100644
index 0000000..97109ce
Binary files /dev/null and b/hw-04/artifacts/screenshots/Screenshot from 2026-08-20 17-51-48.png differ
diff --git a/hw-04/concurrency/pom.xml b/hw-04/concurrency/pom.xml
new file mode 100644
index 0000000..e28074e
--- /dev/null
+++ b/hw-04/concurrency/pom.xml
@@ -0,0 +1,18 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.example</groupId>
+  <artifactId>concurrency</artifactId>
+  <packaging>jar</packaging>
+  <version>1.0-SNAPSHOT</version>
+  <name>concurrency</name>
+  <url>http://maven.apache.org</url>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>
diff --git a/hw-04/concurrency/src/main/java/com/example/DeadLock.java b/hw-04/concurrency/src/main/java/com/example/DeadLock.java
new file mode 100644
index 0000000..3382c06
--- /dev/null
+++ b/hw-04/concurrency/src/main/java/com/example/DeadLock.java
@@ -0,0 +1,47 @@
+package com.example;
+
+import com.example.util.ThreadUtils;
+
+public class DeadLock {
+
+  private static final Object LOCK_A = new Object();
+  private static final Object LOCK_B = new Object();
+
+  public static void main(String[] args) {
+
+    Thread thread1 =
+        new Thread(
+            () -> {
+              synchronized (LOCK_A) {
+                System.out.println("Thread 1: получил LOCK_A");
+
+                ThreadUtils.sleep(100);
+
+                System.out.println("Thread 1: пытается получить LOCK_B");
+
+                synchronized (LOCK_B) {
+                  System.out.println("Thread 1: получил LOCK_B");
+                }
+              }
+            });
+
+    Thread thread2 =
+        new Thread(
+            () -> {
+              synchronized (LOCK_B) {
+                System.out.println("Thread 2: получил LOCK_B");
+
+                ThreadUtils.sleep(100);
+
+                System.out.println("Thread 2: пытается получить LOCK_A");
+
+                synchronized (LOCK_A) {
+                  System.out.println("Thread 2: получил LOCK_A");
+                }
+              }
+            });
+
+    thread1.start();
+    thread2.start();
+  }
+}
diff --git a/hw-04/concurrency/src/main/java/com/example/LiveLock.java b/hw-04/concurrency/src/main/java/com/example/LiveLock.java
new file mode 100644
index 0000000..678748d
--- /dev/null
+++ b/hw-04/concurrency/src/main/java/com/example/LiveLock.java
@@ -0,0 +1,36 @@
+package com.example;
+
+import com.example.util.ThreadUtils;
+
+public class LiveLock {
+
+  private static boolean thread1WantsToPass = true;
+  private static boolean thread2WantsToPass = true;
+
+  public static void main(String[] args) {
+    Thread thread1 =
+        new Thread(
+            () -> {
+              while (thread1WantsToPass) {
+                System.out.println("Поток 1: Я уступаю дорогу Потоку 2...");
+                ThreadUtils.sleep(100);
+              }
+
+              System.out.println("Поток 1 прошел!");
+            });
+
+    Thread thread2 =
+        new Thread(
+            () -> {
+              while (thread2WantsToPass) {
+                System.out.println("Поток 2: Я уступаю дорогу Потоку 1...");
+                ThreadUtils.sleep(100);
+              }
+
+              System.out.println("Поток 2 прошел!");
+            });
+
+    thread1.start();
+    thread2.start();
+  }
+}
diff --git a/hw-04/concurrency/src/main/java/com/example/ThreadUtils.java b/hw-04/concurrency/src/main/java/com/example/ThreadUtils.java
new file mode 100644
index 0000000..018fa9f
--- /dev/null
+++ b/hw-04/concurrency/src/main/java/com/example/ThreadUtils.java
@@ -0,0 +1,12 @@
+package com.example.util;
+
+public class ThreadUtils {
+
+  public static void sleep(long millis) {
+    try {
+      Thread.sleep(millis);
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+    }
+  }
+}
diff --git a/hw-04/concurrency/src/main/java/com/example/TwoThreads.java b/hw-04/concurrency/src/main/java/com/example/TwoThreads.java
new file mode 100644
index 0000000..fbaf02b
--- /dev/null
+++ b/hw-04/concurrency/src/main/java/com/example/TwoThreads.java
@@ -0,0 +1,55 @@
+package com.example;
+
+public class TwoThreads {
+
+  private static final Object lock = new Object();
+  private static boolean turnOne = true;
+
+  public static void main(String[] args) {
+
+    Thread thread1 =
+        new Thread(
+            () -> {
+              while (true) {
+                synchronized (lock) {
+                  while (!turnOne) {
+                    try {
+                      lock.wait();
+                    } catch (InterruptedException e) {
+                      Thread.currentThread().interrupt();
+                      return;
+                    }
+                  }
+
+                  System.out.print("1");
+                  turnOne = false;
+                  lock.notifyAll();
+                }
+              }
+            });
+
+    Thread thread2 =
+        new Thread(
+            () -> {
+              while (true) {
+                synchronized (lock) {
+                  while (turnOne) {
+                    try {
+                      lock.wait();
+                    } catch (InterruptedException e) {
+                      Thread.currentThread().interrupt();
+                      return;
+                    }
+                  }
+
+                  System.out.print("2");
+                  turnOne = true;
+                  lock.notifyAll();
+                }
+              }
+            });
+
+    thread1.start();
+    thread2.start();
+  }
+}