diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..5f81826
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+.idea
+.gradle
+build/
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..a1866fa
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,4 @@
+language: java
+
+jdk:
+- oraclejdk8
\ No newline at end of file
diff --git a/README.md b/README.md
deleted file mode 100644
index e69de29..0000000
diff --git a/build.gradle b/build.gradle
new file mode 100644
index 0000000..2cedd6c
--- /dev/null
+++ b/build.gradle
@@ -0,0 +1,15 @@
+group 'spbau.shevchenko'
+version '1.0-SNAPSHOT'
+
+apply plugin: 'java'
+
+//noinspection GroovyUnusedAssignment
+sourceCompatibility = 1.8
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testCompile group: 'junit', name: 'junit', version: '4.11'
+}
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..ca78035
Binary files /dev/null and b/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..c3a86f7
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,6 @@
+#Thu Mar 02 20:22:38 MSK 2017
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-2.13-all.zip
diff --git a/gradlew b/gradlew
new file mode 100755
index 0000000..27309d9
--- /dev/null
+++ b/gradlew
@@ -0,0 +1,164 @@
+#!/usr/bin/env bash
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn ( ) {
+    echo "$*"
+}
+
+die ( ) {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Split up the JVM_OPTS And GRADLE_OPTS values into an array, following the shell quoting and substitution rules
+function splitJvmOpts() {
+    JVM_OPTS=("$@")
+}
+eval splitJvmOpts $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS
+JVM_OPTS[${#JVM_OPTS[*]}]="-Dorg.gradle.appname=$APP_BASE_NAME"
+
+exec "$JAVACMD" "${JVM_OPTS[@]}" -classpath "$CLASSPATH" org.gradle.wrapper.GradleWrapperMain "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 0000000..832fdb6
--- /dev/null
+++ b/gradlew.bat
@@ -0,0 +1,90 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+if "%@eval[2+2]" == "4" goto 4NT_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+goto execute
+
+:4NT_args
+@rem Get arguments from the 4NT Shell from JP Software
+set CMD_LINE_ARGS=%$
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/settings.gradle b/settings.gradle
new file mode 100644
index 0000000..c9285fe
--- /dev/null
+++ b/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = 'Lazy'
+
diff --git a/src/main/java/ru/spbau/shevchenko/Lazy.java b/src/main/java/ru/spbau/shevchenko/Lazy.java
new file mode 100644
index 0000000..df5d138
--- /dev/null
+++ b/src/main/java/ru/spbau/shevchenko/Lazy.java
@@ -0,0 +1,17 @@
+package ru.spbau.shevchenko;
+
+/**
+ * An object that holds a result of lazy computation.
+ *
+ * It should be the same object on all calls of {@link Lazy#get() ru.spbau.shevchenko.Lazy::get()} method.
+ *
+ * @param <T> type of a result of computation
+ */
+@SuppressWarnings("WeakerAccess")
+public interface Lazy<T> {
+    /**
+     * Method that performs computation.
+     * @return result of computation
+     */
+    T get();
+}
diff --git a/src/main/java/ru/spbau/shevchenko/LazyFactory.java b/src/main/java/ru/spbau/shevchenko/LazyFactory.java
new file mode 100644
index 0000000..8695a55
--- /dev/null
+++ b/src/main/java/ru/spbau/shevchenko/LazyFactory.java
@@ -0,0 +1,44 @@
+package ru.spbau.shevchenko;
+
+import java.util.function.Supplier;
+
+/**
+ * Class ru.spbau.shevchenko.LazyFactory provides factory methods for creating instances of different {@link Lazy} implementations.
+ */
+public class LazyFactory {
+    private LazyFactory(){}
+
+    /**
+     * Returns {@link Lazy} object suitable for use in a single thread.
+     * It's guaranteed, that computation will be done only once.
+     * @param supplier computation to perform
+     * @param <T> type of computation result
+     * @return result of computation
+     */
+    public static <T> Lazy<T> createSingleThreadedLazy(Supplier<T> supplier){
+        return new SingleThreadedLazy<>(supplier);
+    }
+
+    /**
+     * Returns {@link Lazy} object suitable for use in multiple threads.
+     * It's guaranteed, that computation will be done only once.
+     * @param supplier computation to perform.
+     * @param <T> type of computation result
+     * @return result of computation
+     */
+    public static <T> Lazy<T> createMultiThreadedLazy(Supplier<T> supplier){
+        return new MultiThreadedLazy<>(supplier);
+    }
+
+    /**
+     * Returns {@link Lazy} object suitable for use in multiple threads.
+     * No locks on object will be done.
+     * Computation may be performed several times but resulting object will always be the same
+     * @param supplier computation to perform.
+     * @param <T> type of computation result
+     * @return result of computation
+     */
+    public static <T> Lazy<T> createLockFreeLazy(Supplier<T> supplier){
+        return new LockFreeLazy<>(supplier);
+    }
+}
diff --git a/src/main/java/ru/spbau/shevchenko/LockFreeLazy.java b/src/main/java/ru/spbau/shevchenko/LockFreeLazy.java
new file mode 100644
index 0000000..6e5ac8e
--- /dev/null
+++ b/src/main/java/ru/spbau/shevchenko/LockFreeLazy.java
@@ -0,0 +1,42 @@
+package ru.spbau.shevchenko;
+
+import javax.xml.ws.Holder;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+import java.util.function.Supplier;
+
+/**
+ * Lock-free implementation of {@link Lazy} interface suitable when you need to call {@link #get()} in multiple threads.
+ * @param <T> type of a result of computation
+ */
+@SuppressWarnings("WeakerAccess")
+public class LockFreeLazy<T> implements Lazy<T> {
+    private Supplier<T> supplier = null;
+    private volatile Holder<T> result = null;
+
+    @SuppressWarnings("AtomicFieldUpdaterIssues")
+    private static final AtomicReferenceFieldUpdater<LockFreeLazy, Holder> resultUpdater =
+            AtomicReferenceFieldUpdater.newUpdater(LockFreeLazy.class, Holder.class, "result");
+
+    /**
+     * Creates holder for a lazy computation provided by a {@link Supplier} object.
+     * @param supplier computation provider
+     */
+    public LockFreeLazy(Supplier<T> supplier) {
+        this.supplier = supplier;
+    }
+
+
+    /**
+     * Returns result of a computation.
+     * Computation may be performed several times, but this method will always return the same object.
+     * @return result of a computations
+     */
+    @Override
+    public T get() {
+        if (result == null) {
+            final Holder<T> value = new Holder<>(supplier.get());
+            resultUpdater.compareAndSet(this, null, value);
+        }
+        return result.value;
+    }
+}
diff --git a/src/main/java/ru/spbau/shevchenko/MultiThreadedLazy.java b/src/main/java/ru/spbau/shevchenko/MultiThreadedLazy.java
new file mode 100644
index 0000000..ec0c7bc
--- /dev/null
+++ b/src/main/java/ru/spbau/shevchenko/MultiThreadedLazy.java
@@ -0,0 +1,40 @@
+package ru.spbau.shevchenko;
+
+import javax.xml.ws.Holder;
+import java.util.function.Supplier;
+
+/**
+ * Implementation of {@link Lazy} interface suitable when you need to call {@link #get()} in multiple threads.
+ * @param <T> type of a result of computation
+ */
+@SuppressWarnings("WeakerAccess")
+public class MultiThreadedLazy<T> implements Lazy<T> {
+    private Supplier<T> supplier = null;
+    private volatile Holder<T> result = null;
+
+    /**
+     * Creates holder for a lazy computation provided by a {@link Supplier} object.
+     * @param supplier computation provider
+     */
+    public MultiThreadedLazy(Supplier<T> supplier) {
+        this.supplier = supplier;
+    }
+
+    /**
+     * Returns result of a computation.
+     * It's guaranteed that computation will be performed only once.
+     * @return result of a computations
+     */
+    @Override
+    public T get() {
+        if (result == null) {
+            synchronized (this){
+                if (result == null) {
+                    result = new Holder<>(supplier.get());
+                    supplier = null;
+                }
+            }
+        }
+        return result.value;
+    }
+}
diff --git a/src/main/java/ru/spbau/shevchenko/SingleThreadedLazy.java b/src/main/java/ru/spbau/shevchenko/SingleThreadedLazy.java
new file mode 100644
index 0000000..d137f22
--- /dev/null
+++ b/src/main/java/ru/spbau/shevchenko/SingleThreadedLazy.java
@@ -0,0 +1,37 @@
+package ru.spbau.shevchenko;
+
+import javax.xml.ws.Holder;
+import java.util.function.Supplier;
+
+/**
+ * Implementation of {@link Lazy} interface suitable when you only need to call {@link #get()} in single thread.
+ * @param <T> type of a result of computation
+ */
+
+@SuppressWarnings("WeakerAccess")
+public class SingleThreadedLazy<T> implements Lazy<T> {
+    private Supplier<T> supplier = null;
+    private Holder<T> result = null;
+
+    /**
+     * Creates holder for a lazy computation provided by a {@link Supplier} object.
+     * @param supplier computation provider
+     */
+    public SingleThreadedLazy(Supplier<T> supplier) {
+        this.supplier = supplier;
+    }
+
+    /**
+     * Returns result of a computation.
+     * It's guaranteed that computation will be performed only once.
+     * @return result of a computation
+     */
+    @Override
+    public T get() {
+        if (result == null){
+            result = new Holder<>(supplier.get());
+            supplier = null;
+        }
+        return result.value;
+    }
+}
diff --git a/src/main/java/ru/spbau/shevchenko/package-info.java b/src/main/java/ru/spbau/shevchenko/package-info.java
new file mode 100644
index 0000000..ce8438b
--- /dev/null
+++ b/src/main/java/ru/spbau/shevchenko/package-info.java
@@ -0,0 +1,7 @@
+/**
+ * Package with Lazy interface and its implementations.
+ */
+
+package ru.spbau.shevchenko;
+
+
diff --git a/src/test/java/ru/spbau/shevchenko/LazyFactoryTest.java b/src/test/java/ru/spbau/shevchenko/LazyFactoryTest.java
new file mode 100644
index 0000000..682d7db
--- /dev/null
+++ b/src/test/java/ru/spbau/shevchenko/LazyFactoryTest.java
@@ -0,0 +1,96 @@
+package ru.spbau.shevchenko;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Supplier;
+
+import static org.junit.Assert.assertEquals;
+
+
+public class LazyFactoryTest {
+    private static final int THREAD_NUMBER = 10;
+
+    private class NaturalNumbersSupplier implements Supplier<Integer> {
+        private int current = 1;
+        @Override
+        public Integer get() {
+            return current++;
+        }
+    };
+    private static final Supplier<Object> oneTimeNullSupplier = new Supplier<Object>() {
+        private int timesCalled = 0;
+
+        @Override
+        public Object get(){
+            if (timesCalled == 0) {
+                return null;
+            }
+            else {
+                throw new RuntimeException();
+            }
+        }
+    };
+
+
+    @Test
+    public void testSingleThreadedIfSame() throws Exception {
+        testIfSame(LazyFactory.createSingleThreadedLazy(new NaturalNumbersSupplier()), 1);
+    }
+    @Test
+    public void testMultiThreadedIfSame() throws Exception {
+        testIfSame(LazyFactory.createMultiThreadedLazy(new NaturalNumbersSupplier()), 1);
+    }
+    @Test
+    public void testLockFreeIfSame() throws Exception {
+        testIfSame(LazyFactory.createLockFreeLazy(new NaturalNumbersSupplier()), 1);
+    }
+    @Test
+    public void testSingleThreadedOnNull() throws Exception {
+        testOnNull(LazyFactory.createSingleThreadedLazy(oneTimeNullSupplier));
+    }
+    @Test
+    public void testMultiThreadedOnNull() throws Exception {
+        testOnNull(LazyFactory.createMultiThreadedLazy(oneTimeNullSupplier));
+    }
+    @Test
+    public void testLockFreeOnNull() throws Exception {
+        testOnNull(LazyFactory.createLockFreeLazy(oneTimeNullSupplier));
+    }
+
+
+
+    @Test
+    public void testMultiThreadedRaces() throws InterruptedException {
+        testInMultipleThreads(LazyFactory.createMultiThreadedLazy(new NaturalNumbersSupplier()));
+    }
+    @Test
+    public void testLockFreeRaces() throws InterruptedException {
+        testInMultipleThreads(LazyFactory.createLockFreeLazy(new NaturalNumbersSupplier()));
+    }
+
+    private void testInMultipleThreads(Lazy<Integer> oneLazy) throws InterruptedException {
+        final List<Thread> threads = new ArrayList<>();
+        final Runnable runnable = () -> testIfSame(oneLazy, 1);
+        for (int i = 0; i < THREAD_NUMBER; i++) {
+            final Thread thread = new Thread(runnable);
+            thread.start();
+            threads.add(thread);
+        }
+        for (Thread thread : threads) {
+            thread.join();
+        }
+    }
+
+    private void testOnNull(Lazy<Object> nullLazy) {
+        assertEquals(null, nullLazy.get());
+        assertEquals(null, nullLazy.get());
+    }
+    private void testIfSame(Lazy<Integer> lazyOne, Integer expected) {
+        assertEquals(expected, lazyOne.get());
+        assertEquals(expected, lazyOne.get());
+
+    }
+
+}
\ No newline at end of file