ClassCastExcep,该如何处理

ClassCastExcep
package GenericDemo;

import java.util.Iterator;
import java.util.TreeSet;

public class GenericDemo1 {
public static void main(String[] args){
TreeSet<Person1> al1=new TreeSet<Person1>();
al1.add(new Person1("sfdf",23));
al1.add(new Person1("adf",24));
al1.add(new Person1("rfdf",25));
TreeSet<Worker1> al2=new TreeSet<Worker1>();
al1.add(new Worker1("tf",23));
al1.add(new Worker1("4df",24));
al1.add(new Worker1("yfdf",25));
TreeSet<Student1> al3=new TreeSet<Student1>();
al1.add(new Student1("sfdf",23));
al1.add(new Student1("adf",24));
al1.add(new Student1("rfdf",25));
Iterator<Worker1> it=al2.iterator();

while(it.hasNext()){
System.out.println(it.next());
}
}
}
package GenericDemo;

public class Student1 extends Person1 {

public Student1() {
super();
// TODO Auto-generated constructor stub
}

@Override
public String toString() {
return "Student1 [toString()=" + super.toString() + "]";
}

public Student1(String name, int age) {
super(name, age);
// TODO Auto-generated constructor stub
}

}



package GenericDemo;

public class Worker1 extends Person1 {

public Worker1() {
super();
// TODO Auto-generated constructor stub
}

public Worker1(String name, int age) {
super(name, age);
// TODO Auto-generated constructor stub
}

@Override
public String toString() {

return super.toString();
}


}












是的,粘贴粘的..TreeSet<Worker1> al2=new TreeSet<Worker1>();
al1.add(new Worker1("tf",23));
al1.add(new Worker1("4df",24));
al1.add(new Worker1("yfdf",25));
TreeSet<Student1> al3=new TreeSet<Student1>();
al1.add(new Student1("sfdf",23));
al1.add(new Student1("adf",24));
al1.add(new Student1("rfdf",25));
是不是写错了？ClassCaseException 类型转换异常，楼主哪里用到了类型转换，仔细看看。