标签：cert 操作 类对象 orm 1.2 介绍 抽象类 代码 etc
编译器无法优化反射相关的代码，所以导致反射较慢；
stack_flow
Because reflection involves types that are
dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which are called frequently in performance-sensitive applications.
因为反射是动态调用类型(type)，所以jvm优化器无法对其进行优化。因此反射操作拖慢了性能，我盟应该避免在频繁操作且性能敏感的区域使用反射。
如一下简单内部类A，使用两种方式创建三百万次实例并放进数组中，性能差异较大：前者43 ns，后者217 ns：
测试代码：
package reflect;
/**
* @author 杜艮魁
* @date 2018/1/25
*/
public class Run {
private static final int RUNS = 3000000;
public static class A {
}
public static void main(String[] args) throws Exception {
doRegular();
doReflection();
doRegular();
doReflection();//这里貌似给优化了
}
public static void doRegular() throws Exception {
A[] as = new A[RUNS];
long start = System.nanoTime();
for (int i = 0; i < RUNS; i++) {
as[i] = new A();
}
System.out.printf("new A(), %,d ns%n", (System.nanoTime() - start)/RUNS);
}
public static void doReflection() throws Exception {
A[] as = new A[RUNS];
long start = System.nanoTime();
for (int i = 0; i < RUNS; i++) {
as[i] = A.class.newInstance();
}
System.out.printf("A.class.newInstance(), %,d ns%n", (System.nanoTime() - start)/RUNS);
}
}获取“无参构造函数”对象和“有参构造函数”对象
//抽象类和接口都无法实例化；
Class clz=Class.forName("reflect.Ele");
//返回一个无参实例，而且Class的newInstance()方法只有无参的
Ele instrument=(Ele)clz.newInstance();
//有构造参数有参类对象使用反射创建对象的方式
Class clzX=Class.forName("reflect.Handler");
Constructor cons=clzX.getConstructor(int.class);//此方法参数为可变参数，写的是构造函数的参数Class类
Handler objWithParam=(Handler)cons.newInstance(1);
System.out.println(objWithParam.num);标签：cert 操作 类对象 orm 1.2 介绍 抽象类 代码 etc
原文地址：https://www.cnblogs.com/dugk/p/8900813.html
