代码中有的地方看不懂啊 - 黑马程序员技术交流社区

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class ReflectTest {
public static void main(String[] args)throws Exception {
String str = "abcde";
Constructor constructor = String.class.getConstructor(StringBuffer.class);
String str2 = (String)constructor.newInstance(new StringBuffer("abcdef"));
System.out.println(str.charAt(3));
ReflectPoint rp1 = new ReflectPoint(7,8);
Field fieldy = rp1.getClass().getField("y");
System.out.println(fieldy.get(rp1));
Field fieldx = rp1.getClass().getDeclaredField("x");
fieldx.setAccessible(true);
System.out.println(fieldx.get(rp1));
changeStringValue(rp1);
System.out.println(rp1);
Method methodCharAt = String.class.getMethod("charAt",int.class);
System.out.println(methodCharAt.invoke(str, 1));
System.out.println(methodCharAt.invoke(str, new Object[]{3}));
String startClassName = args[0];
//这里老是报错，可是明明是按照张孝祥老师的代码写的啊，而且怎么检查都没看出哪里错了
Method mainMethod = Class.forName(startClassName).getMethod("main",String[].class);
mainMethod.invoke(null,(Object)new String[]{"dsa","xzvdd","13124"});
mainMethod.invoke(null,new Object[]{new String[]{"dsa","xzvdd","13124"}});
}
public static void changeStringValue(Object obj) throws Exception{
Field[] fields = obj.getClass().getFields();
for(Field field : fields){
if(field.getType() == String.class){
String oldvalue = (String)field.get(obj);
String newvalue = oldvalue.replace('b', 'a');
field.set(obj, newvalue);//这里是将新的字符串重新赋给obj吗？
}
}
}
}
class TestArguments{
public static void main(String[] args){
for(String arg : args){
System.out.println(arg);
}
}
}
public class ReflectPoint {
public String str1 = "baeioahi";
public String str2 = "bjoabjaboaiaobbbba";
public String str3 = "rwqwrqwqw";
@Override
public String toString() {
return "ReflectPoint [str1=" + str1 + ", str2=" + str2 + ", str3=" + str3 + "]";
}
}

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