public class BaseBt {
    public BaseBt() {
        System.out.println("BaseBt构造");
    }
    public void disPlay(){
        System.out.println("BaseBt");
    }
}

public class CircularBt  extends BaseBt{
    public void disPlay(){
        System.out.println("CircularBt");
    }
}

public class SquareBt extends BaseBt{
    public void disPlay(){
        System.out.println("SquareBt");
    }
}

public class TriangleBt extends BaseBt{
    public void disPlay(){
        System.out.println("TriangleBt");
    }
}

package button;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
/**
 * @ProjectName: ArcfaceDemo
 * @Package: button
 * @ClassName: txttest
 * @Description: java类作用描述
 * @Author: 作者名
 * @CreateDate: 2021/9/28 0028 下午 10:43
 * @UpdateUser: 更新者：
 * @UpdateDate: 2021/9/28 0028 下午 10:43
 */
public class txttest {
    /**
     * 读取txt文件的内容
     * @param file 想要读取的文件对象
     * @return 返回文件内容
     */
    ///C:\butType.txt
    public static String txt2String(File file){
        StringBuilder result = new StringBuilder();
        try{
            BufferedReader br = new BufferedReader(new FileReader(file));//构造一个BufferedReader类来读取文件
            String s = null;
            while((s = br.readLine())!=null){//使用readLine方法，一次读一行
//                result.append(System.lineSeparator()+s);
                result.append(s);
            }
            br.close();
        }catch(Exception e){
            e.printStackTrace();
        }
        return result.toString();
    }
    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        File file = new File("C:\butType.txt");
        String byTypeClass=txt2String(file);
        System.out.println(byTypeClass);
        BaseBt baseBt = (BaseBt) Class.forName(byTypeClass).newInstance();
        baseBt.disPlay();
    }
}

使用Class.forName(byTypeClass).newInstance();过程中总是不行，一定要进行debug；发现路径不对；对了/n;