带有可选字段的 Java 对象

Question

我有一个场景，请看

句子可以是:

String Subject + String Verb + String Object

String Subject + String Verb + String Adverb+ String Object

String Subject + String Verb + String Adjective+ String Object

String Subject + String Verb

我想创建一个 Sentence 类对象。

  Sentence s = new Sentence();
    s.setSubject();
    ...

现在，我可以保留 Sentence 类中的所有字段，但我想确保没有字段必须为空。 我想从我在我创建对象的地方初始化的字段创建任何类型的句子。

eg: 
Sentence s = new Sentence();
s.setSubject();
s.setVerb();
s.setObject();
s.getValue(); // will return sentence value as S+V+O as I have set SVO

Sentence s = new Sentence();
s.setSubject();
s.setVerb();
s.getValue(); // will return sentence value as S+V as I have set SV

等等...我可以在 java 中做这样的事情吗？

基本上，我想避免未初始化的字段和空指针。

编辑

请注意，如果我将字段留空，即 ""或 null ，则形成的句子将类似于

“我没有上学。”或(动词为 null)。

“我正在学校”(动词是空)。

所以，请在回答之前考虑这种情况。

Answer 1

我更喜欢使用构建器模式，让最终用户更清楚地使用并避免错误

    Public class Sentence {

        private String subject;
        private String verb;
        private String adjective;
        private String object;

    //package private to ensure no one can call it outside package, canbe made pvt as well
        Sentence(String subject, String verb, String adjective, String object) {
            this.subject = subject;
            this.verb = verb;
            this.adjective = adjective;
            this.object = object;
        }

        public static class SentenceBuilder{
            private String subject;
            private String verb;
            private String adjective;
            private String object;

            private static final String EMPTY = "";

            private String sanitizeInput(String input){
                if (input==null){
                    return EMPTY;
                }
                return input;
            }

            private String validateInput(String input){
                if(input==null || input.isEmpty()){
                    throw new IllegalArgumentException("cant be null or empty"); 
                }
                return input;
            }

            public SentenceBuilder(String subject, String verb) {
                this.subject = validateInput(subject);
                this.verb = validateInput(verb);
            }

            public SentenceBuilder adjective(String adjective){
                this.adjective = sanitizeInput(adjective);
                return this;
            }

            public SentenceBuilder object(String object){
                this.object = sanitizeInput(object);
                return this;
            }

            public Sentence build(){
                return new Sentence(subject,verb,adjective,object);
            }
        }

        public static void main(String[] args) {
//sample usage            
Sentence sentence = new SentenceBuilder("subject","verb")
                    .adjective("adjective")
                    .object("object")
                    .build();
        }
    }