findbyID 返回可选。 将此 object 设置为另一个 object 会导致错误

Question

    
    public String addStudyProgram(){
        
        Optional<StudyProgram> program = studyProgramRepository.findById(1);        

            Student student = new Student();        
            student.setStudentName("Mushashi");
            
            student.setProgram(program);    // error The method setProgram(StudyProgram) in the type Student is not applicable for the arguments (Optional<StudyProgram>)   
        
        return "Done";
    }

student and program are DTO, if i change setProgram(StudyProgram) method to setProgram(Optional) then it interfere with database scheme. what will be the solution?

Answer 1

program is Optional, use program.get() for getting object value: student.setProgram(program.get());

Answer 2

Optional<Object> is not the actual Object . You can use obj.get() if you're sure that the value is present in the Optional . To avoid such an occurrence and be null safe, you can use obj.orElse(defaultValue) which will return the defaultValue as an Object instance.