Class GenericsExamples

java.lang.Object

net.jrodolfo.java_evolution.java05.GenericsExamples

public class GenericsExamples
extends Object

Demonstrates generics, introduced in Java 5.

Before generics, collections usually stored Object values. Callers had to cast values back to the expected type, so type mistakes could survive until runtime. Generics move that check into the type system.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	GenericsExamples.LanguageFeature	Language-level feature used by the wildcard example.
static interface	GenericsExamples.NamedFeature	First capability required by the multiple-bound example.
static class	GenericsExamples.PlatformFeature	Platform-level feature used by the wildcard example.
static interface	GenericsExamples.PrioritizedFeature	Second capability required by the multiple-bound example.
static class	GenericsExamples.RankedFeature	Concrete type that satisfies both bounds.
static interface	GenericsExamples.ReleaseFeature	Base type for the bounded wildcard example.

Constructor Summary

Constructors

Constructor	Description
GenericsExamples()

Method Summary

Modifier and Type	Method	Description
<T extends GenericsExamples.NamedFeature & GenericsExamples.PrioritizedFeature> String	describePrioritizedFeature(T feature)	Describes a value whose type parameter has multiple bounds.
<T> T	first(List<T> values)	Returns the first element from a typed list without a cast.
String	firstRawValue(List rawValues)	Shows the old raw-list shape that generics were designed to replace.
int	totalImportance(Iterable<? extends GenericsExamples.ReleaseFeature> features)	Reads feature importance from any iterable producer of GenericsExamples.ReleaseFeature values or subtypes.
List<String>	typedNames(List<String> names)	Creates a typed list of names.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

GenericsExamples

public GenericsExamples()

Method Details

typedNames

public List<String> typedNames(List<String> names)

Creates a typed list of names.

Parameters:

names - names to copy

Returns:

a new list whose element type is known to the compiler

first

public <T> T first(List<T> values)

Returns the first element from a typed list without a cast.

Type Parameters:

T - the list element type

Parameters:

values - values to inspect

Returns:

the first value

firstRawValue

public String firstRawValue(List rawValues)

Shows the old raw-list shape that generics were designed to replace.

Parameters:

rawValues - raw values without an element type

Returns:

the first value cast to String

totalImportance

public int totalImportance(Iterable<? extends GenericsExamples.ReleaseFeature> features)

Reads feature importance from any iterable producer of GenericsExamples.ReleaseFeature values or subtypes.

The ? extends ReleaseFeature wildcard says this method only reads feature values. That makes the API flexible: callers can pass Iterable<LanguageFeature> or Iterable<PlatformFeature> without copying those values into a less specific collection first.

Parameters:

features - features to inspect

Returns:

total importance score

describePrioritizedFeature

public <T extends GenericsExamples.NamedFeature & GenericsExamples.PrioritizedFeature>
String describePrioritizedFeature(T feature)

Describes a value whose type parameter has multiple bounds.

<T extends NamedFeature & PrioritizedFeature> is a multiple-bound type parameter. It lets the method require both capabilities without inventing a separate combined interface. This is one place where Java exposes an intersection-type-style constraint in normal source code.

Type Parameters:

T - type that satisfies both bounds

Parameters:

feature - feature that has both a name and a priority

Returns:

human-readable feature description