关于Java中反射机制的深入讲解

public class foo{

  foo(){

   //构造方法

  }

}

public foo method(){

  //...

}

public static void main(string[] args) {

//foo的实例对象，new 就出来了

foo foo1 = new foo();

//如何表示？

//第一种：告诉我们任何一个类都有一个隐含的静态成员变量class

class c1 = foo. class ;

//第二种:已经知道该类的对象通过getclass方法

class c2 = foo1.getclass();

system.out.println(c1 == c2);

//第三种：动态加载

class c3 = null ;

try {

  c3 = class .forname( "cn.zyzpp.reflect.foo" );

} catch (classnotfoundexception e) {

  e.printstacktrace();

}

system.out.println(c2 == c3);

}

//此时c1 c2 c3为class的实例对象

  try {

//  foo foo = (foo)c1.newinstance();

   foo foo = (foo)c3.newinstance();

   foo.print();

  } catch (instantiationexception e) {

   e.printstacktrace();

  } catch (illegalaccessexception e) {

   e.printstacktrace();

  }

public class office {

  public void print() {

  system.out.println( "office" );

  }

}

public class loading {

  public static void main(string[] args) {

  try {

   //在运行时再动态加载类

   //arg[0] 为java执行命令时传的参数

   class <?> a = class .forname(args[ 0 ]);

   office office = (office) a.newinstance();

   office.print();

  } catch (classnotfoundexception e) {

   e.printstacktrace();

  } catch (illegalaccessexception e) {

   e.printstacktrace();

  } catch (instantiationexception e) {

   e.printstacktrace();

  }

  }

}

private void printclassmessage(object obj){

//要获取类的信息，首先获取类的类类型

class clazz = obj.getclass();

//获取类的名称

system.out.println(modifier.tostring(clazz.getmodifiers())+ " " + clazz.getclass().getname()+ " " +clazz.getname()+ "{" );

system.out.println( "----构造方法----" );

//构造方法

constructor[] constructors = clazz.getdeclaredconstructors();

for (constructor constructor: constructors){

  //构造方法修饰符与名字

  system.out.print(modifier.tostring(constructor.getmodifiers())+ " " +constructor.getname()+ "(" );

  //构造函数的所有参数类型

  class [] parametertypes = constructor.getparametertypes();

  for ( class c: parametertypes){

  system.out.print(c.getname()+ ", " );

  }

  system.out.println( "){}" );

}

system.out.println( "----成员变量----" );

//成员变量

field[] fields = clazz.getdeclaredfields();

for (field field: fields){

  system.out.println( " " +modifier.tostring(field.getmodifiers())+ " " +field.gettype().getname() + " " + field.getname()+ ";" );

}

system.out.println( "----成员方法----" );

//method类，方法对象,一个成员方法就是一个method对象

method[] methods = clazz.getdeclaredmethods();

for (method method : methods){

  //获取方法返回类型

  class returntype = method.getreturntype();

  //获取方法上的所有注释

  annotation[] annotations = method.getannotations();

  for (annotation annotation: annotations){

  //打印注释类型

  system.out.println( " @" +annotation.annotationtype().getname()+ " " );

  }

  //打印方法声明

  system.out.print( " " +modifier.tostring(returntype.getmodifiers())+ " " +returntype.getname()+ " " +method.getname()+ "(" );

  //获取方法的所有参数类型

  class <?>[] parametertypes = method.getparametertypes();

  //获取方法的所有参数

  parameter[] parameters = method.getparameters();

  for (parameter parameter: parameters){

  //参数的类型，形参（全是arg123..）

  system.out.print(parameter.gettype().getname()+ " " +parameter.getname()+ ", " );

  }

  system.out.println( ")" );

}

system.out.println( "}" );

}

public class foo{

  public void print(string name, int num) {

  system.out.println( "i am " +name+ " age " +num);

  }

}

class clazz = foo. class ;

method method = clazz.getmethod( "print" , new class []{string. class , int . class });

object o = method.invoke( new foo(), new object[]{ "name" , 20 });

public static void main(string[] args) {

  arraylist<string> stringarraylist = new arraylist<>();

  stringarraylist.add( "hello" );

  arraylist arraylist = new arraylist();

  class c1 = stringarraylist.getclass();

  class c2 = arraylist.getclass();

  system.out.println(c1 == c2);

}

public static void main(string[] args) {

  arraylist<string> stringarraylist = new arraylist<>();

  stringarraylist.add( "hello" );

  arraylist arraylist = new arraylist();

  class c1 = stringarraylist.getclass();

  class c2 = arraylist.getclass();

  system.out.println(c1 == c2);

  try {

   method method = c1.getmethod( "add" ,object. class );

   method.invoke(stringarraylist, 20 );

   system.out.println(stringarraylist.tostring());

  } catch (nosuchmethodexception e) {

   e.printstacktrace();

  } catch (illegalaccessexception e) {

   e.printstacktrace();

  } catch (invocationtargetexception e) {

   e.printstacktrace();

  }

}