java 利用反射修改对象中的list类型字段中的值。

    Grade grade=new Grade();
    Field f=Grade.class.getDeclaredField("name");
    f.setAccessible(true);
    f.set(grade, "三年级一班");

public class Grade {
    private String name;
    private List<Student> students;
    
    public Grade(){}
    public Grade(String name,List<Student> students){
        this.name=name;
        this.students=students;
    }
    public String toString(){
        StringBuilder sb=new StringBuilder();
        for(Student s : students){
            sb.append(s.getNumberid()+"    ");
        }
        return sb.toString();
    }
}

public class Student {
    private String name;
    private int age;
    private String numberid;
    public String getNumberid(){
        return numberid;
    }
}

public class Program {
    public static void main(String[] args) throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InstantiationException{
        Grade grade=new Grade();
        
        Field f=Grade.class.getDeclaredField("name");
        f.setAccessible(true);
        f.set(grade, "三年级一班");
        
        Field field=Grade.class.getDeclaredField("students");
        if(List.class.isAssignableFrom(field.getType())){
            List arraylist=new ArrayList();
            
            Type type=field.getGenericType();
            //这样判断type 是不是参数化类型。 如Collection<String>就是一个参数化类型。
            if(type instanceof ParameterizedType){
                //获取类型的类型参数类型。  你可以去查看jdk帮助文档对ParameterizedType的解释。
                Class clazz=(Class)((ParameterizedType) type).getActualTypeArguments()[0];
                Object obj=clazz.newInstance();
                Field ff=clazz.getDeclaredField("numberid");
                ff.setAccessible(true);
                ff.set(obj, "1001010");
                arraylist.add(obj);
            }
            field.setAccessible(true);
            field.set(grade, arraylist);
        }
        System.out.println(grade);
    }
}