Java反射机制-学习笔记1(一)

Java 中，定义一个Class，然后就可以通过new 关键字，将Class 实例化，从而得到一个实例对象；

那么反射，刚好相反，是通过一个Class的实例对象，来得到Class 类的相关信息.

实例1： 通过一个实例对象，获得完整的包名和类名

[java]
package org.zhang.test;

class Demo{

}
public class ReflectTest {
public static void main(String[] args) {
Demo demo = new Demo();
System.out.println(demo.getClass().getName());
}
}
运行结果：org.zhang.test.Demo

实例2：所有类的对象都是Class 的实例

[java]
package org.zhang.test;

class Demo {

}

public class ReflectTest {
public static void main(String[] args){
Class< > c1 = null;
Class< > c2 = null;
Class< > c3 = null;
try {
c1 = Class.forName("org.zhang.test.Demo");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}

c2 = (new Demo()).getClass();
c3 = Demo.class;

assert c1 != null;
System.out.println(c1.getName());
System.out.println(c2.getName());
System.out.println(c3.getName());
}
}

结果：
org.zhang.test.Demo
org.zhang.test.Demo
org.zhang.test.Demo
其中：Class< > 等同于 Class。 定义泛型的时候，如：class User { }

实例3： 通过Class，实例化 类的对象

[java]
package org.zhang.test;
class Person{
private String name;
private int age;

@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}
}

public class ReflectTest {
public static void main(String[] args){
Class< > personClass = null;
Person person = null;
try {
personClass = Class.forName("org.zhang.test.Person");
person = (Person) personClass.newInstance();

} catch (ClassNotFoundException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
} catch (InstantiationException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
} catch (IllegalAccessException e) {
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}

assert person != null;
person.setName("zhangwenan");
person.setAge(25);
System.out.println(person);

}
}

结果：
Person{name='zhangwenan', age=25}

实例4：通过Class 调用不同的构造方法

[java]
package org.zhang.test;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

class Person{
private String name = "no name";
private int age = 0;

public Person(String name) {
this.name = name;
}

public Person(int age) {
this.age = age;
}

public Person(String name, int age) {
this.name = name;
this.age = age;
}

public Person() {
}


@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public in