CIS 270—Application Development II Chapter 18-Generics

Introduction Generic ________ allow the programmer to specify, in a single method declaration, a set of related methods. e.g., one generic method could sort arrays of different types Generic ________ allow the programmer to specify, in a single class declaration, a set of related types. e.g., one generic class could be used to instantiate array objects for an array of Integers, Doubles, Strings, etc. Compile-time type _______ could be enforced so that an array stores elements of the same type. Generics only work with ___________ data types.

Motivation for Generic Methods Separate methods, all called printArray, can be defined to print the elements of any type of array, such as Integer[], Double[], or Character[]. public static void printArray( Integer[] inputArray ) { for ( Integer element : inputArray ) System.out.printf( "%s ", element ); System.out.println(); } // see Fig for complete program It would be convenient to define one printArray method for any array of generic type E[] and have the Java compiler determine the data types of different arrays used in an application.

Generic Methods: Implementation Following is an implementation of a generic method: public static void printArray( E[] inputArray ) { for ( E element : inputArray ) System.out.printf( "%s ", element ); System.out.println(); } The E is an arbitrary type ___________ that serves as a placeholder for an actual argument. The compiler checks the program to set up method calls to printArray for different data types. The compiler also checks for valid operations.

Type Parameters as Return Types See Fig public static > T maximum( T x, T y, T z ) // first T is return type { T max = x; // assume x is the largest if ( y.compareTo( max ) > 0 ) max = y; // y is the largest so far if ( z.compareTo( max ) > 0 ) max = z; // z is the largest return max; // returns the largest object } // end method maximum If primitives are sent to maximum, the compiler _________ them as objects (and compareTo is valid).

Overloading Generic Methods A class can have two different generic methods with the same name, but different method parameters. A generic method can be overloaded by non-generic methods of the same name and number of parameters. The compiler first looks for an exact match of method names and argument types. If an exact match isn’t found, the compiler looks for __________. _________ is the process whereby the compiler replaces type parameters with actual types. Type parameters can have an upper _________.

Generic Classes A generic class is used to describe something in a type-independent manner. You can specify the actual types that should be used in place of the class’s ______ parameter(s). For example, one generic Stack class could be used to create many Stack classes. A stack is a data structure (list of elements) with a ______ (last in, first out) organization. An element is pushed onto the stack and popped off of the stack (like dishes in a stack of dishes). Fig presents a generic Stack class declaration that uses an array of type E to implement the Stack.

Raw Types If a class is instantiated without specifying the type argument, Java will use type Object. Stack objectStack = new Stack( 5 ); instead of Stack doubleStack = new Stack ( 5 ); This ensures ___________ compatibility with earlier versions of Java. A raw type Stack variable can be assigned a generic stack: Stack rawTypeStack = new Stack ( 5 ); A generic type Stack variable can be assigned a raw type, but it is ____________: Stack integerStack = new Stack( 10 );