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Java example source code file (AbstractIteratorTest.java)

This example Java source code file (AbstractIteratorTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractiterator, illegalstateexception, integer, iterator, nosuchelementexception, object, override, runtimeexception, should, somecheckedexception, someuncheckedexception, suppresswarnings, testcase, util

The AbstractIteratorTest.java Java example source code

/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.base;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.testing.GcFinalization;

import junit.framework.TestCase;

import java.lang.ref.WeakReference;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Unit test for {@code AbstractIterator}.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible(emulated = true)
// TODO(cpovirk): why is this slow (>1m/test) under GWT when fully optimized?
public class AbstractIteratorTest extends TestCase {

  public void testDefaultBehaviorOfNextAndHasNext() {

    // This sample AbstractIterator returns 0 on the first call, 1 on the
    // second, then signals that it's reached the end of the data
    Iterator<Integer> iter = new AbstractIterator() {
      private int rep;
      @Override public Integer computeNext() {
        switch (rep++) {
          case 0:
            return 0;
          case 1:
            return 1;
          case 2:
            return endOfData();
          default:
            fail("Should not have been invoked again");
            return null;
        }
      }
    };

    assertTrue(iter.hasNext());
    assertEquals(0, (int) iter.next());

    // verify idempotence of hasNext()
    assertTrue(iter.hasNext());
    assertTrue(iter.hasNext());
    assertTrue(iter.hasNext());
    assertEquals(1, (int) iter.next());

    assertFalse(iter.hasNext());

    // Make sure computeNext() doesn't get invoked again
    assertFalse(iter.hasNext());

    try {
      iter.next();
      fail("no exception thrown");
    } catch (NoSuchElementException expected) {
    }
  }

  public void testSneakyThrow() throws Exception {
    Iterator<Integer> iter = new AbstractIterator() {
      boolean haveBeenCalled;
      @Override public Integer computeNext() {
        if (haveBeenCalled) {
          fail("Should not have been called again");
        } else {
          haveBeenCalled = true;
          sneakyThrow(new SomeCheckedException());
        }
        return null; // never reached
      }
    };

    // The first time, the sneakily-thrown exception comes out
    try {
      iter.hasNext();
      fail("No exception thrown");
    } catch (Exception e) {
      if (!(e instanceof SomeCheckedException)) {
        throw e;
      }
    }

    // But the second time, AbstractIterator itself throws an ISE
    try {
      iter.hasNext();
      fail("No exception thrown");
    } catch (IllegalStateException expected) {
    }
  }

  public void testException() {
    final SomeUncheckedException exception = new SomeUncheckedException();
    Iterator<Integer> iter = new AbstractIterator() {
      @Override public Integer computeNext() {
        throw exception;
      }
    };

    // It should pass through untouched
    try {
      iter.hasNext();
      fail("No exception thrown");
    } catch (SomeUncheckedException e) {
      assertSame(exception, e);
    }
  }

  public void testExceptionAfterEndOfData() {
    Iterator<Integer> iter =
        new AbstractIterator<Integer>() {
          @Override
          public Integer computeNext() {
            endOfData();
            throw new SomeUncheckedException();
          }
        };
    try {
      iter.hasNext();
      fail("No exception thrown");
    } catch (SomeUncheckedException expected) {
    }
  }

  public void testCantRemove() {
    Iterator<Integer> iter =
        new AbstractIterator<Integer>() {
          boolean haveBeenCalled;

          @Override
          public Integer computeNext() {
            if (haveBeenCalled) {
              endOfData();
            }
            haveBeenCalled = true;
            return 0;
          }
        };

    assertEquals(0, (int) iter.next());

    try {
      iter.remove();
      fail("No exception thrown");
    } catch (UnsupportedOperationException expected) {
    }
  }

  @GwtIncompatible // weak references
  public void testFreesNextReference() {
    Iterator<Object> itr = new AbstractIterator() {
      @Override public Object computeNext() {
        return new Object();
      }
    };
    WeakReference<Object> ref = new WeakReference(itr.next());
    GcFinalization.awaitClear(ref);
  }

  public void testReentrantHasNext() {
    Iterator<Integer> iter =
        new AbstractIterator<Integer>() {
          @Override
          protected Integer computeNext() {
            boolean unused = hasNext();
            return null;
          }
        };
    try {
      iter.hasNext();
      fail();
    } catch (IllegalStateException expected) {
    }
  }

  // Technically we should test other reentrant scenarios (4 combinations of
  // hasNext/next), but we'll cop out for now, knowing that
  // next() both start by invoking hasNext() anyway.

  /**
   * Throws a undeclared checked exception.
   */
  private static void sneakyThrow(Throwable t) {
    class SneakyThrower<T extends Throwable> {
      @SuppressWarnings("unchecked") // intentionally unsafe for test
      void throwIt(Throwable t) throws T {
        throw (T) t;
      }
    }
    new SneakyThrower<Error>().throwIt(t);
  }

  private static class SomeCheckedException extends Exception {
  }

  private static class SomeUncheckedException extends RuntimeException {
  }
}

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