oracle PLS-000103如何解决此错误

Question

private String studentId;

public void setStudentId(String studentId){


if(studentId != null && studentId.trim().length() > 0 && studentId != " " ){
    if(studentId.charAt(0) == 'a'){
        this.name = studentId;
}
}
else{
    System.out.println("Error. NOt Valid.");
}