Java Polymorphism: Wrappers and Interfaces in CMSC 131 Fall 2008 - Prof. Bonnie J. Dorr, Study notes of Computer Science

Download Java Polymorphism: Wrappers and Interfaces in CMSC 131 Fall 2008 - Prof. Bonnie J. Dorr and more Study notes Computer Science in PDF only on Docsity! 1 CMSC 131 Fall 2008 Jan Plane (Adapted from Bonnie Dorr) Lecture Set #14: Polymorphism Introduction 1. Wrappers 2. Interfaces CMSC 131 Fall 2008 Jan Plane (Adapted from Bonnie Dorr) 1 Wrappers
We may want to treat primitives as though they were objects
For example, generic routines can be implemented using interfaces … but they are not usable on primitive types
To overcome this problem, Java provides wrappers for primitive types
Wrappers: classes whose objects contain single values of the “wrapped type”
Wrappers also contain other useful conversion operations (to / from String, etc.)
Wrappers included in java.lang:
Byte
Short
Integer
Long
Float
Double
Character
Boolean 2 CMSC 131 Fall 2008 Jan Plane (Adapted from Bonnie Dorr) 2 The Integer Wrapper
The documentation is on-line at http://java.sun.com/j2se/1.5.0/docs/api/
Notes
Immutable
Constructors
Implements Comparable
Documentation says “Comparable<Integer>”
Comparable in Java 5.0 is a interface
Has compareTo method. CMSC 131 Fall 2008 Jan Plane (Adapted from Bonnie Dorr) 3 Code Re-use
Many operations recur in programming
sorting
max / min (These operations may apply to strings, numbers, etc.)
Desirable: one implementation!
Less coding
Less likely to have typos
Easier maintenance of code