multiple bounds example

Author: tobyweston

src/main/java/s4j/java/chapter14/MultipleBounds.java

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+/*
+ * Copyright (c) 2015-2017 Toby Weston
+ *
+ * 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 s4j.java.chapter14;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class MultipleBounds {
+
+	// sets two upper bounds to the generic type A
+	public static <A extends Animal & Comparable<Animal>> void sort(List<A> list) {
+		Collections.sort(list);
+	}
+
+	public static void main(String... args) {
+
+		List<Lion> enclosure = new ArrayList<>();
+		enclosure.add(new Lion());
+		enclosure.add(new Lion());
+		sort(enclosure);
+
+		List<Animal> zoo = new ArrayList<>();
+		zoo.add(new Lion());
+		zoo.add(new Lion());
+		zoo.add(new Zebra());
+		sort(zoo);
+	}
+
+
+	static class Animal implements Comparable<Animal> {
+		@Override
+		public int compareTo(Animal o) {
+			return 0;
+		}
+	}
+
+	static class Lion extends Animal { }
+	static class Zebra extends Animal { }
+
+}

src/main/scala/s4j/scala/chapter14/MultipleBounds.scala

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+/*
+ * Copyright (c) 2015-2017 Toby Weston
+ *
+ * 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 s4j.scala.chapter14
+
+class MultipleBounds {
+
+  // we can't set two upper bounds like we can in Java but we can say the bound type
+  // must also extend certain traits
+  def sort[A <: Lion with Comparable[Animal]](list: List[A]) = { }
+
+  def main(args: String*) {
+
+    var enclosure = List[Lion]()
+    enclosure = new Lion +: enclosure
+    enclosure = new Lion +: enclosure
+    // sort[Lion, Animal](enclosure)      // compiler error
+    sort(enclosure)                       // must remove the type hints
+
+//    var zoo = List[Animal]()
+//    zoo = new Zebra +: zoo
+//    zoo = new Lion +: zoo
+//    zoo = new Lion +: zoo
+//    sort(zoo)
+  }
+
+  class Animal extends Comparable[Animal] {
+    def compareTo(o: Animal): Int = 0
+  }
+  class Lion extends Animal
+  class Zebra extends Animal
+}