Java 反射经常用法演示样例

Posted 2020-09-22 cxchanpin

<pre name="code" class="java">import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

class Point{
	int x;
	private int y;
	
	public Point(){
		x = 1;
		y = 2;
	}	
	
	public void setX(int x) {
		this.x = x;
	}

	public void setY(int y) {
		this.y = y;
	}

	private Point(int x){
		this();
		this.x = x;
	}
	
	public Point(int x, int y) {
		super();
		this.x = x;
		this.y = y;
	}
	
	public void printPoint(){
		System.out.println("x = " + x + " , y = " + y);
	}
}

public class ReflectTest2 {

	public static void main(String[] args) throws Exception {
		
		//使用第一种方法创建对象
		Class cls1 = Class.forName("Point");
		Constructor con1 = cls1.getConstructor(int.class,int.class);
		Point p1 = (Point) con1.newInstance(5,6);
		p1.printPoint();
		
		//使用另外一种方法创建对象
		Class cls2 = Point.class;
		Point p2 = (Point) cls2.newInstance();//无參构造函数
		p2.printPoint();
		
		//使用第三种方法创建对象
		Class cls3 = p1.getClass();
		//使用p1对象的setX方法将x值改动为10
		Method m1 = cls3.getMethod("setX", int.class);
		m1.invoke(p1, 10);
		p1.printPoint();
		
		/*
		 * Note:
		 * getDeclaredConstructor能够返回指定參数的构造函数，
		 * 而getConstructor仅仅能放回指定參数的public的构造函数 
		 * */		
		Constructor con2 = cls3.getDeclaredConstructor(int.class);
		//訪问私有变量、函数须要设置accessible
		con2.setAccessible(true);
		Point p4 = (Point) con2.newInstance(3);
		p4.printPoint();
		
		//Field f1 = cls3.getField("y");//error
		Field f1 = cls3.getDeclaredField("y");
		f1.setAccessible(true);
		//获取p1的y值
		System.out.println(f1.get(p1));
	}

}