8032056: Create demo to illustrate new practices of the default methods usage

Reviewed-by: briangoetz, rfield, psandoz
Contributed-by: taras.ledkov@oracle.com

src/share/sample/lambda/DefaultMethods/ArrayIterator.java

+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *   - Neither the name of Oracle nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * The code sample illustrates the usage of default methods in the JDK 8. Most
+ * implementations of {@link Iterator} don't provide a useful
+ * {@link Iterator#remove()} method, however,
+ * they still have to implement this method to throw
+ * an UnsupportedOperationException. With the default method, the same
+ * default behavior in interface Iterator itself can be provided.
+ */
+public class ArrayIterator {
+
+    /** Close the constructor because ArrayIterator is part of the utility
+     * class.
+     */
+    protected ArrayIterator() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Returns an iterator that goes over the elements in the array.
+     *
+     * @param <E> type of an array element
+     * @param array source array to iterate over it
+     * @return an iterator that goes over the elements in the array
+     */
+    public static <E> Iterator<E> iterator(final E[] array) {
+        return new Iterator<E>() {
+            /**
+             * Index of the current position
+             *
+             */
+            private int index = 0;
+
+            /**
+             * Returns the next element in the iteration
+             *
+             * @return the next element in the iteration
+             * @throws NoSuchElementException if the iteration has no more
+             * elements
+             */
+            @Override
+            public boolean hasNext() {
+                return (index < array.length);
+            }
+
+            /**
+             * Returns {@code true} if the iteration has more elements. (In
+             * other words, returns {@code true} if {@link #next} returns
+             * an element, rather than throwing an exception.)
+             *
+             * @return {@code true} if the iteration has more elements
+             */
+            @Override
+            public E next() {
+                if (!hasNext()) {
+                    throw new NoSuchElementException();
+                }
+                return array[index++];
+            }
+
+            /**
+             * This method does not need to be overwritten in JDK 8.
+             */
+            //@Override
+            //public void remove() {
+            //    throw UnsupportedOperationException(
+            //            "Arrays don't support remove.")
+            //}
+        };
+    }
+
+    /**
+     * Sample usage of the ArrayIterator
+     *
+     * @param args command-line arguments
+     */
+    public static void main(final String[] args) {
+        Iterator<String> it = ArrayIterator.iterator(
+                new String[]{"one", "two", "three"});
+
+        while (it.hasNext()) {
+            System.out.println(it.next());
+        }
+    }
+}

src/share/sample/lambda/DefaultMethods/DiamondInheritance.java

+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *   - Neither the name of Oracle nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * This sample diamond interface inheritance with <b>default methods</b>.
+ * If there's not already a unique method implementation to inherit,
+ * you must provide it. The inheritance diagram is similar to the following:
+ * <pre>
+ *                   Animal
+ *                    /   \
+ *                 Horse   Bird
+ *                    \   /
+ *                   Pegasus
+ * </pre>
+ *
+ * Both {@link Horse} and {@link Bird} interfaces implements the <code>go</code>
+ * method. The {@link Pegasus} class have to overrides the
+ * <code>go</code> method.
+ *
+ * The new syntax of super-call is used here:
+ * <pre>
+ *     &lt;interface_name&gt;.super.&lt;method&gt;(...);
+ *     For example:  Horse.super.go();
+ * </pre> So, Pegasus moves like a horse.
+ */
+public class DiamondInheritance {
+
+    /**
+     * Base interface to illustrate the diamond inheritance.
+     *
+     * @see DiamondInheritance
+     */
+    public interface Animal {
+
+        /**
+         * Return string representation of the "go" action for concrete animal
+         *
+         * @return string representation of the "go" action for concrete animal
+         */
+        String go();
+    }
+
+    /**
+     * Interface to illustrate the diamond inheritance.
+     *
+     * @see DiamondInheritance
+     */
+    public interface Horse extends Animal {
+
+        /**
+         * Return string representation of the "go" action for horse
+         *
+         * @return string representation of the "go" action for horse
+         */
+        @Override
+        default String go() {
+            return this.getClass().getSimpleName() + " walks on four legs";
+        }
+    }
+
+    /**
+     * Interface to illustrate the diamond inheritance.
+     *
+     * @see DiamondInheritance
+     */
+    public interface Bird extends Animal {
+
+        /**
+         * Return string representation of the "go" action for bird
+         *
+         * @return string representation of the "go" action for bird
+         */
+        @Override
+        default String go() {
+            return this.getClass().getSimpleName() + " walks on two legs";
+        }
+
+        /**
+         * Return string representation of the "fly" action for bird
+         *
+         * @return string representation of the "fly" action for bird
+         */
+        default String fly() {
+            return "I can fly";
+        }
+    }
+
+    /**
+     * Class to illustrate the diamond inheritance. Pegasus must mix horse and
+     * bird behavior.
+     *
+     * @see DiamondInheritance
+     */
+    public static class Pegasus implements Horse, Bird {
+
+        /**
+         * Return string representation of the "go" action for the fictitious
+         * creature Pegasus
+         *
+         * @return string representation of the "go" action for the fictitious
+         * creature Pegasus
+         */
+        @Override
+        public String go() {
+            return Horse.super.go();
+        }
+    }
+
+    /**
+     * Illustrate the behavior of the {@link Pegasus} class
+     *
+     * @param args command line arguments
+     */
+    public static void main(final String[] args) {
+        System.out.println(new Pegasus().go());
+    }
+}

src/share/sample/lambda/DefaultMethods/Inheritance.java

+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *   - Neither the name of Oracle nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * The sample illustrates rules to resolve conflicts between inheritance
+ * candidates with <b>default methods</b>. There are two simple rules:
+ * <ul>
+ * <li>Class wins. If the superclass has a concrete or abstract declaration of
+ * this method, then it is preferred over all defaults.</li>
+ * <li>Subtype wins. If an interface extends another interface, and both provide
+ * a default, then the more specific interface wins. </li>
+ * </ul>
+ */
+public class Inheritance {
+
+    /**
+     * The behavior of an creature that can swim
+     */
+    public interface Swimable {
+
+        /**
+         * Return string representation of the swim action for a creature that
+         * can swim
+         *
+         * @return string representation of the swim action for a creature
+         * that can swim
+         */
+        default String swim() {
+            return "I can swim.";
+        }
+    }
+
+    /**
+     * The abstract class that overrides {@link #swim} method
+     */
+    public abstract static class Fish implements Swimable {
+
+        /**
+         * Return string representation of the swim action for a fish
+         *
+         * @return string representation of the swim action for a fish
+         */
+        @Override
+        public String swim() {
+            return this.getClass().getSimpleName() + " swims under water";
+        }
+    }
+
+    /**
+     * This class is used for the illustration rule of 1. See the source code
+     * of the {@link #main} method.
+     * <pre>
+     *      System.out.println(new Tuna().swim()); //"Tuna swims under water" output is suspected here
+     * </pre>
+     */
+    public static class Tuna extends Fish implements Swimable {
+    }
+
+    /**
+     * The behavior of an creature that can dive: the interface that overrides
+     * {@link #swim} method (subtype of {@link Swimable})
+     */
+    public interface Diveable extends Swimable {
+
+        /**
+         * Return string representation of the swim action for a creature that
+         * can dive
+         *
+         * @return string representation of the swim action for a creature
+         * that can dive
+         */
+        @Override
+        default String swim() {
+            return "I can swim on the surface of the water.";
+        }
+
+        /**
+         * Return string representation of the dive action for a creature that
+         * can dive
+         *
+         * @return string representation of the dive action for a creature
+         * that can dive
+         */
+        default String dive() {
+            return "I can dive.";
+        }
+    }
+
+    /**
+     * This class is used for the illustration of rule 2. See the source code
+     * of the {@link #main} method
+     * <pre>
+     *      //"I can swim on the surface of the water." output is suspected here
+     *      System.out.println(new Duck().swim());
+     * </pre>
+     */
+    public static class Duck implements Swimable, Diveable {
+    }
+
+    /**
+     * Illustrate behavior of the classes: {@link Tuna} and {@link Duck}
+     *
+     * @param args command line arguments
+     */
+    public static void main(final String[] args) {
+        // Illustrates rule 1. The Fish.swim() implementation wins
+        //"Tuna swims under water" is output
+        System.out.println(new Tuna().swim());
+
+        // Illustrates rule 2. The Diveable.swim() implementation wins
+        //"I can swim on the surface of the water." is output
+        System.out.println(new Duck().swim());
+    }
+}

src/share/sample/lambda/DefaultMethods/MixIn.java

+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *   - Neither the name of Oracle nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+import java.io.IOException;
+import java.lang.reflect.Field;
+
+/**
+ * The example illustrates how to use the default method for mixin.
+ * @see BuildType
+ * @see Debuggable
+ */
+public class MixIn {
+
+    /**
+     * Implement this interface for a class that must be in debug print
+     */
+    public interface Debuggable {
+
+        /**
+         * Print the class name and all fields to a string. Uses reflection to
+         * obtain and access fields of this object.
+         *
+         * @return the string formatted like the following: <pre>
+         * State of the: &lt;Class Name&gt;
+         * &lt;member name&gt; : &lt;value&gt;
+         * ...
+         * </pre>
+         */
+        default String toDebugString() {
+            StringBuilder sb = new StringBuilder();
+            sb.append("State of the: ").append(
+                    this.getClass().getSimpleName()).append("\n");
+            for (Class cls = this.getClass();
+                    cls != null;
+                    cls = cls.getSuperclass()) {
+                for (Field f : cls.getDeclaredFields()) {
+                    try {
+                        f.setAccessible(true);
+                        sb.append(f.getName()).append(" : ").
+                                append(f.get(this)).append("\n");
+                    } catch (IllegalAccessException e) {
+                    }
+                }
+            }
+            return sb.toString();
+        }
+    }
+
+    /**
+     * Sample exception class to demonstrate mixin. This enum inherits the
+     * behavior of the {@link Debuggable}
+     */
+    public static enum BuildType implements Debuggable {
+
+        BUILD(0, "-build"),
+        PLAN(0, "-plan"),
+        EXCLUDE(1, "-exclude"),
+        TOTAL(2, "-total");
+
+        private final int compareOrder;
+        private final String pathSuffix;
+
+        private BuildType(int compareOrder, String pathSuffix) {
+            this.compareOrder = compareOrder;
+            this.pathSuffix = pathSuffix;
+        }
+
+        public int getCompareOrder() {
+            return compareOrder;
+        }
+
+        public String getPathSuffix() {
+            return pathSuffix;
+        }
+    }
+
+    /**
+     * Illustrate the behavior of the MixClass
+     *
+     * @param args command-line arguments
+     * @throws java.io.IOException internal demo error
+     */
+    public static void main(final String[] args) throws IOException {
+        System.out.println(BuildType.BUILD.toDebugString());
+    }
+}

src/share/sample/lambda/DefaultMethods/Reflection.java

+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *   - Neither the name of Oracle nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.stream.Stream;
+
+/**
+ * The code sample illustrates changes in the reflection API linked
+ * <b>default methods</b>. Since Java SE 8, a new method is added into the class
+ * <b><code>java.lang.reflect.Method</code></b>, with which you can reflectively
+ * determine whether or not a default method provided by an interface
+ * (<b><code>Method.isDefault()</code></b>).
+ */
+public class Reflection {
+
+    /**
+     * Base interface to illustrate the new reflection API.
+     *
+     * @see Dog
+     */
+    public interface Animal {
+
+        /**
+         * Return string representation of the eat action for Animal
+         *
+         * @return string representation of the eat action for Animal
+         */
+        default String eat() {
+            return this.getClass().getSimpleName()
+                    + " eats like an ordinary animal";
+        }
+
+        /**
+         * Return string representation of the sleep action for Animal
+         *
+         * @return string representation of the sleep action for Animal
+         */
+        default String sleep() {
+            return this.getClass().getSimpleName()
+                    + " sleeps like an ordinary animal";
+        }
+
+        /**
+         * Return string representation of the go action for Animal
+         *
+         * @return string representation of the go action for Animal
+         */
+        String go();
+    }
+
+    /**
+     * Dog class to illustrate the new reflection API. You can see that:
+     * <ul>
+     * <li> the {@link #go} and {@link #sleep} methods are not default.
+     * {@link #go} is not the default implementation and the {@link #sleep}
+     * method implementation wins as subtype (according with {@link Inheritance}
+     * rule. 2) </li>
+     * <li> the {@link #eat} is a simple default method that is not overridden
+     * in this class.
+     * </li>
+     * </ul>
+     */
+    public static class Dog implements Animal {
+
+        /**
+         * Return string representation of the go action for Dog
+         *
+         * @return string representation of the go action for Dog
+         */
+        @Override
+        public String go() {
+            return "Dog walks on four legs";
+        }
+
+        /**
+         * Return string representation of the sleep action for Dog
+         *
+         * @return string representation of the sleep action for Dog
+         */
+        @Override
+        public String sleep() {
+            return "Dog sleeps";
+        }
+    }
+
+    /**
+     * Illustrate the usage of the method java.lang.reflect.Method.isDefault()
+     *
+     * @param args command-line arguments
+     * @throws NoSuchMethodException internal demo error
+     */
+    public static void main(final String[] args) throws NoSuchMethodException {
+        Dog dog = new Dog();
+        Stream.of(Dog.class.getMethod("eat"), Dog.class.getMethod("go"), Dog.class.getMethod("sleep"))
+                .forEach((m) -> {
+                    System.out.println("Method name:   " + m.getName());
+                    System.out.println("    isDefault: " + m.isDefault());
+                    System.out.print("    invoke:    ");
+                    try {
+                        m.invoke(dog);
+                    } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException ex) {
+                    }
+                    System.out.println();
+                });
+    }
+}

src/share/sample/lambda/DefaultMethods/SimplestUsage.java

+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   - Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   - Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ *   - Neither the name of Oracle nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * The sample illustrates the simplest use case of the <b>default methods</b>.
+ */
+public class SimplestUsage {
+
+    /**
+     * The Animal interface provides the default implementation
+     * of the {@link #eat} method.
+     */
+    public interface Animal {
+
+        /**
+         * Return string representation of the eat action for Animal
+         *
+         * @return string representation of the eat action for Animal
+         */
+        default String eat() {
+            return this.getClass().getSimpleName()
+                    + " eats like an ordinary animal";
+        }
+    }
+
+    /**
+     * The Dog class doesn't have its own implementation of the {@link #eat}
+     * method and uses the default implementation.
+     */
+    public static class Dog implements Animal {
+    }
+
+    /**
+     * The Mosquito class implements {@link #eat} method, its own implementation
+     * overrides the default implementation.
+     *
+     */
+    public static class Mosquito implements Animal {
+
+        /**
+         * Return string representation of the eat action for Mosquito
+         *
+         * @return string representation of the eat action for Mosquito
+         */
+        @Override
+        public String eat() {
+            return "Mosquito consumes blood";
+        }
+    }
+
+    /**
+     * Illustrate behavior of the classes: {@link Dog} and {@link Mosquito}
+     *
+     * @param args command-line arguments
+     */
+    public static void main(String[] args) {
+        // "Dog eats like an ordinary animal" is output
+        System.out.println(new Dog().eat());
+
+        // "Mosquito consumes blood" is output
+        System.out.println(new Mosquito().eat());
+    }
+}