利用List删除数据有错，怎么解决啊？

import com.etc.entity.Staff;
public class DeleteStaff {
    private static List<Staff> staffList = new ArrayList<Staff>();
    public void deleteSatff(String num) {
        InsertStaff insertStaff = new InsertStaff();
        staffList = insertStaff.getList();
        for (Staff s : staffList) {
            if (s.getNum().equals(num)) {
                staffList.remove(s);
            }
            System.out.println("员工" + s.getName() + "已删除");
        }
    }
}
//这是Staff
public class Staff {
    private String num;
    private String name;
    private String salary;
    public Staff() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Staff(String num, String name, String salary) {
        super();
        this.num = num;
        this.name = name;
        this.salary = salary;
    }
    @Override
    public String toString() {
        return "Staff [num=" + num + ", name=" + name + ", salary=" + salary + "]";
    }
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSalary() {
        return salary;
    }
    public void setSalary(String salary) {
        this.salary = salary;
    }
}