Java Reflection API | Java.lang.Class-优快云博客

本文介绍了Java反射API的基本概念，包括其定义、用途及局限性。文章详细解释了反射包中的主要类和接口，并通过示例展示了如何使用Class类来获取运行时类的信息，如构造函数、方法等。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

ref: http://www.studytonight.com/java/reflection-api

Reflection API

reflection means ability of a software to analyze itself. In java, Reflection API provides facility to analyze and change runtime behavior of a class, at runtime

For Example, using reflection at the runtime you can determine what method or modifiers a class supports

What is reflect package ?

java.lang.reflect package encapsulates serveral important interface and classes. These classes and interface define methods which are used for reflection

class　　　　　　　　　　　　description

----------------------------------------------------------------------------------------------------------

Array　　　　　　　　　　　　allow you to dynamically created and manipulate arrays

Constructor　　　　　　　　　gives info abt constructor of a class

Field　　　　　　　　　　　　 provides info abt field

Method　　　　　　　　　　　 procide info abt method

Modifier　　　　　　　　　　　provide info abt class and member access modifier

Proxy　　　　　　　　　　　　 supports dynamic proxy classes

java.lang.Class is another important class used in Reflection API

Uses of Reflection

1. Developing IDE
2. Debugging and Test tools

3. Loading drivers and providing dynamic info

Disadvantages of Reflection

1. Low performance

2. Security risk

3. Violation of OOPs concept

************************* cut**************************

Reflection Class

java.lang.Class

Class is a final class injava.lang package which extends Object class. Instance of this class

represents classes and interfaces in a running java application. It is used to analyze and change dynamic behavior of a class at runtime

Some Important Methods of java.lang.Class class

This class defines several methods using which we can get info about methods, constructors, modifiers and members of a class at runtime

forName()　　　　

1. this method takes fully qualified name of classes or nterfaces as its argument and return instance

of the class associated with it.

2. static Class<?> forName(String className)

class Student{}
class Test
{
 public static void main(String args[])
 {
  Class c = Class.forName("Student");
  System.out.println(c.getName());
 }
}
output: Student

getConstructors() and getDeclaredConstructors()

1. getConstructors() returns array of Constructors object that represent all the public constructors of the invoking object. This method only returns public constructor. getDeclaredConstructors() will return all constructors

Constructor< ?>[] getConstructors();
Constructor< ?>[] getDeclaredConstructors();

Example using getConstructors() and getDeclaredConstructors() method

Class c = Class.forName("Student");
  Constructor< Student>[] ct = c.getConstructors();
  for(int i=0; i< ct.length; i++)
    { System.out.println(ct[i]); }
  Constructor< Student>[] cdt = c.getDeclaredConstructors();
  for(int i=0;i< cdt.length;i++)
    { System.out.println(cdt[i]);}

output:

  public Student()
  public Student()
  Student(java.lang.String)

getMethods() and getDeclaredMethods()
getFields() and getDeclaredFields()
Example using getFields() and getDeclaredFields() method

转载于:https://www.cnblogs.com/morningdew/p/5619385.html