反射机制

最新推荐文章于 2023-06-10 09:00:00 发布

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最新推荐文章于 2023-06-10 09:00:00 发布

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分类专栏： JavaSe 文章标签：面试 J# C C++ C#

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本文介绍了一个使用Java反射机制打印类的各种特性的程序示例。该程序可以读取用户输入的类名，然后利用反射API获取并展示该类的构造器、方法及字段等详细信息。

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面试研发工程师易考

写道CoreJAVA中的反射机制

import java.util.*;
import java.lang.reflect.*;

/**
* This program uses reflection to print all features of a class.
* @version 1.1 2004-02-21
* @author Cay Horstmann
*/
public class ReflectionTest
{
public static void main(String[] args)
{
// read class name from command line args or user input
String name;
if (args.length > 0) name = args[0];
else
{
Scanner in = new Scanner(System.in);
System.out.println("Enter class name (e.g. java.util.Date): ");
name = in.next();
}

try
{
// print class name and superclass name (if != Object)
Class cl = Class.forName(name);
Class supercl = cl.getSuperclass();
String modifiers = Modifier.toString(cl.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print("class " + name);
if (supercl != null && supercl != Object.class) System.out.print(" extends "
+ supercl.getName());

System.out.print("\n{\n");
printConstructors(cl);
System.out.println();
printMethods(cl);
System.out.println();
printFields(cl);
System.out.println("}");
}
catch (ClassNotFoundException e)
{
e.printStackTrace();
}
System.exit(0);
}

/**
* Prints all constructors of a class
* @param cl a class
*/
public static void printConstructors(Class cl)
{
Constructor[] constructors = cl.getDeclaredConstructors();

for (Constructor c : constructors)
{
String name = c.getName();
System.out.print(" ");
String modifiers = Modifier.toString(c.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print(name + "(");

// print parameter types
Class[] paramTypes = c.getParameterTypes();
for (int j = 0; j < paramTypes.length; j++)
{
if (j > 0) System.out.print(", ");
System.out.print(paramTypes[j].getName());
}
System.out.println(");");
}
}

/**
* Prints all methods of a class
* @param cl a class
*/
public static void printMethods(Class cl)
{
Method[] methods = cl.getDeclaredMethods();

for (Method m : methods)
{
Class retType = m.getReturnType();
String name = m.getName();

System.out.print(" ");
// print modifiers, return type and method name
String modifiers = Modifier.toString(m.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print(retType.getName() + " " + name + "(");

// print parameter types
Class[] paramTypes = m.getParameterTypes();
for (int j = 0; j < paramTypes.length; j++)
{
if (j > 0) System.out.print(", ");
System.out.print(paramTypes[j].getName());
}
System.out.println(");");
}
}

/**
* Prints all fields of a class
* @param cl a class
*/
public static void printFields(Class cl)
{
Field[] fields = cl.getDeclaredFields();

for (Field f : fields)
{
Class type = f.getType();
String name = f.getName();
System.out.print(" ");
String modifiers = Modifier.toString(f.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.println(type.getName() + " " + name + ";");
}
}
}