Examining Classes - Java Tutorial 5.0 英文版

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Trail: The Reflection API

Lesson: Examining Classes

If you are writing a class browser, you need a way to get information about classes at runtime. For example, you might want to display the names of the class fields, methods, and constructors. Or, you might want to show which interfaces are implemented by a class. To get this information you need to get the Classobject that reflects the class.
For each class, the Java Runtime Environment (JRE) maintains an immutable Class object that contains information about the class. A Class object represents, or reflects, the class. With the reflection API, you can invoke methods on a Class object which return Constructor, Method, and Fieldobjects. You can use these objects to get information about the corresponding constructors, methods, and fields defined in the class.
Class objects also represent interfaces. You invoke Class methods to find out about an interface's modifiers, methods, and public constants. Not all of the Class methods are appropriate when a Class object reflects an interface. For example, it doesn't make sense to invoke getConstructors when the Class object represents an interface. The section Examining Interfaces explains which Class methods you may use to get information about interfaces.

Retrieving Class Objects

First things first. Before you can find out anything about a class, you must first retrieve its corresponding Class object.

Getting the Class Name

It's easy to find out the name of a Class object. All you have to do is invoke the getName method.

Discovering Class Modifiers

This section shows you the methods you need to call to find out what modifiers a particular class has.

Finding Superclasses

In this section you'll learn how to retrieve all of the Class objects for the ancestors of a given class.

Identifying the Interfaces Implemented by a Class

If you want to find out what interfaces a class implements, then check out this section.

Examining Interfaces

In this section you'll learn how to tell if a Class object represents an interface or a class. You'll also get some tips on how to get more information about an interface.

Identifying Class Fields

This section shows you how to discover what fields belong to a class, and how to find out more about these fields by accessing Field objects.

Discovering Class Constructors

This section, which introduces the Constructor class, explains how to get information about a class's contructors.

Obtaining Method Information

To find out about a class's methods, you need to retrieve the corresponding Method objects. This section shows you how to do this.

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