如何检查一个方法是否不为空？

Question

由于我对编程比较陌生，所以我现在不知道如何检查方法是否不为空。在下面的代码中，我需要检查answers.get方法是否不为空，我该如何实现这一点？

public class SharedViewModel extends ViewModel {

private HashMap<Integer, MutableLiveData<String>> answers = new HashMap<>();

public MutableLiveData<String> getAnswer(int questionId) {

    return answers.get(questionId);

}

public void setAnswer(int questionId, String answer) {

    // TODO make sure that answers.get is not null

    answers.get(questionId).setValue(answer);

 }

}

Answer 1

只要在尝试访问该对象或操作它时添加一个null检查即可。answers.get(questionId)public class SharedViewModel extends ViewModel {&nbsp; public void setAnswer(int questionId, String answer) {&nbsp; &nbsp; if(answers.get(questionId)!=null){&nbsp; &nbsp; &nbsp; &nbsp;answers.get(questionId).setValue(answer);&nbsp; &nbsp; &nbsp;}&nbsp; &nbsp;}}如果您使用的是 Java8 及以上版本，您还可以使用//nonNull will return true if object is not nullif(Objects.nonNull(answers.get(questionId))){&nbsp; &nbsp;answers.get(questionId).setValue(answer);}&nbsp;

Answer 2

只是为了添加到现有答案和您的待办事项中，您可能需要使用getOrDefault，answers.getOrDefault(questionId,&nbsp;answer);

Answer 3

一般来说你可以这样做：if(methodname(args)!&nbsp;=null&nbsp;)&nbsp;{//statements}&nbsp;;