关于反射调用toString方法的问题 - 黑马程序员技术交流社区

/**
*
*/
package com.itheima.test;
import java.io.FileInputStream;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Properties;
/**
* @author Administrator
*
*/
public class ReflectTest{
public static void main(String[] args) throws Exception {
InputStream ips=new FileInputStream("config.properties");//从文件中读取类名
Properties pro=new Properties();
pro.load(ips);
ips.close();
String className=pro.getProperty("className");
//得到构造方法
Constructor constructor=Class.forName(className).getConstructor(int.class,int.class);
//使用构造方法得到对象
ReflectPoint point1=(ReflectPoint)constructor.newInstance(1,2);
ReflectPoint point2=(ReflectPoint)constructor.newInstance(2,3);
//得到类中成员变量x对于的类
Field fieldY=Class.forName(className).getField("y");
//输出对象point1，point2对应的y的值
System.out.println(fieldY.get(point1));
System.out.println(fieldY.get(point2));
//得到类中成员变量x对于的类
//Field fieldX=Class.forName(className).getField("x");
//对于private的变量不能直接用getField来得到成员变量，应该使用getDeclaredField
Field fieldX=Class.forName(className).getDeclaredField("x");
//输出对象point1，point2对应的x的值
//因为x还是private，不能直接读取，要设置权限
fieldX.setAccessible(true);
System.out.println(fieldX.get(point1));
System.out.println(fieldX.get(point2));
//下面更改point1中String类型的值，长度如果大于4，就截断
Field[] fields=Class.forName(className).getFields();
//这里先把toString方法用反射的方式得到
Method toStringMethod=Class.forName(className).getMethod("toString");
toStringMethod.invoke(point1);
for(Field field:fields)
if(field.getType()==String.class)//字节码用==判断
{
String oldValue=(String)field.get(point1);
String newValue=oldValue.substring(0, 4);
field.set(point1, newValue);
}
toStringMethod.invoke(point1);
}
}
class ReflectPoint {
private int x;
public int y;
public String str1 = "football";
public String str2 = "basketball";
public String str3 = "itcast";
public ReflectPoint(int x, int y) {
super();
this.x = x;
this.y = y;
}
/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return str1+":"+str2+":"+str3;
}
}

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