Lecture 20 Interfaces Last time 1 Explicit array initialization 2 Arrays as arguments 3 Arrays of objects 4 Privacy leaks 5 Array Copying Today 1 2 Interfaces Wrappers CMSC 131 Fall 2007 Jan Plane Adapted from Bonnie Dorr 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 CMSC 131 Fall 2007 Jan Plane Adapted from Bonnie Dorr 1 Polymorphism Using an interface we can create one variable that can reference objects of different types i e UMStudent variable referencing CSMajor CEMajor or PsychMajor This form of generalization is called polymorphism Hallmark of OO languages Allows application of same code to objects of different types Polymorphism A variable that takes on many shapes Interfaces one mechanism Java provides for polymorphism a collection of prototypes method prototypes but no bodies aka abstract methods A class C implements an interface I if C provides implementations of all of I s abstract methods A class implementing an interface can also provide other methods or implement other interfaces CMSC 131 Fall 2007 Jan Plane Adapted from Bonnie Dorr 2 1 Wrappers We may want to treat primitives as though they were objects For example generic routines like PsychoAnalyze 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 CMSC 131 Fall 2007 Jan Plane Adapted from Bonnie Dorr 3 The Integer Wrapper The documentation is on line at http java sun com j2se 1 5 0 docs api Notes Constructors Implements Comparable Documentation says Comparable Integer Comparable in Java 5 0 is a interface Has compareTo method etc CMSC 131 Fall 2007 Jan Plane Adapted from Bonnie Dorr 4 In class Demo Implementing a method using the Integer class Create objects of type Integer using the constructor can be based on int type values or variables Create an array of Integer type object references and those objects of type Integer use the API to access information about the data in the Integer class CMSC 131 Fall 2007 Jan Plane Adapted from Bonnie Dorr 5 2
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