code: /*
   * Copyright (c) 2019 the Eclipse Milo Authors
   *
   * This program and the accompanying materials are made
   * available under the terms of the Eclipse Public License 2.0
   * which is available at https://www.eclipse.org/legal/epl-2.0/
   *
   * SPDX-License-Identifier: EPL-2.0
   */
  
  package org.eclipse.milo.opcua.stack.core.util;
  
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.function.Supplier;
  
  import org.testng.annotations.Test;
  
  import static org.testng.Assert.assertEquals;
  import static org.testng.Assert.assertNull;
  
  public class LazyTest {
  
      @Test
      public void lazyRetainsNonNullValue() {
          Lazy<Object> lazy = new Lazy<>();
  
          Object instance = new Object();
  
          Object o1 = lazy.getOrCompute(() -> instance);
          assertEquals(o1, instance);
  
          Object o2 = lazy.getOrCompute(() -> instance);
          assertEquals(o2, instance);
      }
  
      @Test
      public void lazyRetainsNullValue() {
          Lazy<Object> lazy = new Lazy<>();
  
          Object o1 = lazy.getOrCompute(() -> null);
  
          assertNull(o1);
      }
  
      @Test
      public void lazyOnlyComputesOnce() {
          Lazy<Object> lazy = new Lazy<>();
  
          final Object instance = new Object();
  
          Supplier<Object> supplier = new Supplier<Object>() {
              final AtomicInteger count = new AtomicInteger(0);
  
              @Override
              public Object get() {
                  if (count.incrementAndGet() != 1) {
                      throw new IllegalStateException();
                  } else {
                      return instance;
                  }
              }
          };
  
          Object o1 = lazy.getOrCompute(supplier);
          assertEquals(o1, instance);
  
          Object o2 = lazy.getOrCompute(supplier);
          assertEquals(o2, instance);
      }
  
      @Test
      public void lazyIsResettable() {
          Lazy<Object> lazy = new Lazy<>();
  
          final Object instance1 = new Object();
          final Object instance2 = new Object();
  
          Supplier<Object> supplier = new Supplier<Object>() {
              final AtomicInteger count = new AtomicInteger(0);
  
              @Override
              public Object get() {
                  switch (count.incrementAndGet()) {
                      case 1:
                          return instance1;
                      case 2:
                      default:
                          return instance2;
                  }
              }
          };
  
          Object o1 = lazy.getOrCompute(supplier);
          assertEquals(o1, instance1);
  
          lazy.reset();
  
          Object o2 = lazy.getOrCompute(supplier);
          assertEquals(o2, instance2);
      }
  
  }
  