字符串截取

public class Teacher implements Serializable {


private static final long serialVersionUID = 1L;
private Integer id;
private String tname;
private String tnumber;
private String tsubject;
         //省略get  set
}
public String getTstrs() {

StringBuilder sb = new StringBuilder();
String sbs=new String();

                  Set<Teacher> teacher=new HashSet<Teacher>();
                  for(Teacher t:teacher){
sb.append(",");
sb.append(t.getTname());
sbs=sb.substring(1);//截取字符串
}
return sbs;
}