Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved L14 (Chapter 21) Generics 2

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Bounded Generic Type public static void main(String[] args ) { Rectangle rectangle = new Rectangle(2, 2); Circle9 circle = new Circle9(2); System.out.println("Same area? " + equalArea(rectangle, circle)); } public static boolean equalArea(E object1, E object2) { return object1.findArea() == object2.findArea(); }

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Raw Type and Backward Compatibility // raw type GenericStack stack = new GenericStack(); This is roughly equivalent to GenericStack stack = new GenericStack ();

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Raw Type is Unsafe Max.max("Welcome", 23); // Max.java: Find a maximum object public class Max { /** Return the maximum between two objects */ public static Comparable max(Comparable o1, Comparable o2) { if (o1.compareTo(o2) > 0) return o1; else return o2; } Runtime Error:

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Make it Safe Max.max("Welcome", 23); // Max1.java: Find a maximum object public class Max1 { /** Return the maximum between two objects */ public static > E max(E o1, E o2) { if (o1.compareTo(o2) > 0) return o1; else return o2; }

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Wildcards WildCardDemo1 Why wildcards are necessary? See this example. ? unbounded wildcard ? Extends T bounded wildcard ? Super T lower bound wildcard: WildCardDemo2WildCardDemo3

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Generic Types and Wildcard Types

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved Important Facts It is important to note that a generic class is shared by all its instances regardless of its actual generic type. GenericStack stack1 = new GenericStack (); GenericStack stack2 = new GenericStack (); Although GenericStack and GenericStack are two types, but there is only one class GenericStack loaded into the JVM.