java反射机制 一
1、通过无参构造实例化对象
package com.njust.zht.Reflection;
public class Dog {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
private String color;
private int age;
public void wangwang(){
System.out.println("汪汪叫。。");
System.out.println("dog name="+name);
System.out.println("dog color="+color);
System.out.println("dog age="+age);
}
}
package com.njust.zht.Test1;
import com.njust.zht.Reflection.Dog;
public class Test1 {
public static void main(String[] args) throws ClassNotFoundException {
Class<?> demo1=null;
// Class<?> demo2=null;
// Class<?> demo3=null;
demo1=Class.forName("com.njust.zht.Reflection.Dog");
Dog dog=null;
try {
dog=(Dog) demo1.newInstance();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
dog.setName("lili");
dog.setColor("black");
dog.setAge(2);
dog.wangwang();
}
}
汪汪叫。。 dog name=lili dog color=black dog age=2
如果在构造函数的时候加上参数，如：
public Dog(){
}
java.lang.InstantiationException: com.njust.zht.Reflection.Dog at java.lang.Class.newInstance(Unknown Source) at com.njust.zht.Test1.Test1.main(Test1.java:16) Exception in thread "main" java.lang.NullPointerException at com.njust.zht.Test1.Test1.main(Test1.java:24)
所以这种方式不能带有参数的构造函数。
2、通过Class调用其他类中的构造函数 （也可以通过这种方式通过Class创建其他类的对象）
package com.njust.zht.Test1;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import com.njust.zht.Reflection.Dog;
public class Test1 {
public static void main(String[] args) throws ClassNotFoundException, IllegalArgumentException, InvocationTargetException {
Class<?> demo=null;
// Class<?> demo2=null;
// Class<?> demo3=null;
demo=Class.forName("com.njust.zht.Reflection.Dog");
Dog dog1=null;
Dog dog2=null;
Dog dog3=null;
Dog dog4=null;
try {
//获取所有的构造函数
Constructor<?> cons[]=demo.getConstructors();
System.out.println(cons[0]);
System.out.println(cons[1]);
System.out.println(cons[2]);
System.out.println(cons[3]);
dog4=(Dog) cons[0].newInstance("niuniu",15,"red");/************************************/
dog3=(Dog) cons[1].newInstance("lolo",20);
dog2=(Dog) cons[2].newInstance("kity");
dog1=(Dog) cons[3].newInstance();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(dog1);
System.out.println(dog2);
System.out.println(dog3);
System.out.println(dog4);
}
}
上面的标记
/************************************/出如果参数设置不对应就会出错。可以先输出下构造函数里面的参数解决。在我这里是按照参数从多到少的顺序配置的。（本人在此处折腾了几个小时，最后想到输出构造函数的方法解决之）如果设置错误就会有如下的错误：
Exception in thread "main" java.lang.IllegalArgumentException: wrong number of arguments
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at javaGXJS.fanShe.reflect.main(dfgfdgfdg.java:45)