如何连续调用一个方法两次？

Question

我有一个代码，在我的 class 中，我希望能够像 qns.answer(5).answer(7) 一样调用方法答案两次。但是现在当我如下调用方法答案时，我得到错误找不到符号。

例如：

Question qns = new Question("How many apples are there in the bag?")
qns ==> How many apples are there in the bag?: My answer is 0.

qns.answer(12)
==> How many apples are there in the bag?: My answer is 12.

qns.answer(12).answer(4)
==> How many apples are there in the bag?: My answer is 4.

qns
qns ==> How many apples are there in the bag?: My answer is 0.

class Question {
    private final String question;
    private final int correctAns;

    public Question(String question, int correctAns) {
        this.question = question;
        this.correctAns = correctAns
    }

    public String answer(int myAns) {
        return String.format("%s: My answer is %d.", this.question, myAns);
    }

    @Override
    public String toString() {
        return String.format("%s: My answer is 0.", this.question);
    }
}

如果您能就如何解决这个问题提供一些指导，我们将不胜感激。

Answer 1

Question可以有一个额外的字段来存储答案，你也可以写一个新的构造函数来初始化那个字段。

private final int currentAns;

public Question(String question, int correctAns, int currentAns) {
    this.question = question;
    this.correctAns = correctAns;
    this.currentAns = currentAns;
}

public Question(String question, int correctAns) {
    this(question, correctAns, 0);
}

// toString can now use currentAns!
@Override
public String toString() {
    return String.format("%s: My answer is %d.", this.question, currentAns);
}

然后在 answer 方法中，您可以 return 一个新的 Question 指定答案为 currentAns:

public Question answer(int myAns) {
    return new Question(question, correctAns, myAns);
}

现在您可以链接多个 ans 调用。如果在它的末尾调用toString（无论是隐式还是显式），就可以得到想要的字符串。

JShell 中的示例：

jshell> Question qns = new Question("How many apples are there in the bag?", 1);

qns ==> How many apples are there in the bag?: My answer is 0.

jshell> qns.answer(12);
 ==> How many apples are there in the bag?: My answer is 12.

jshell> qns.answer(12).answer(4);
 ==> How many apples are there in the bag?: My answer is 4.

jshell> qns
qns ==> How many apples are there in the bag?: My answer is 0.

Answer 2

如果你想在一个对象上多次调用相同或不同的方法（=chaining），你需要return this in方法。

既然你试图实现的目标真的不清楚，我会提出一些建议：

class Question {
    private final String question;
    private final int correctAns;

    private static String format(String quest, int ans) {
        return String.format("%s: My answer is %d.", quest, ans);
    }

    public Question(String question) {
        this.question = question;
        this.correctAns = 0;
    }

    public String answer(int myAns) {
        this.correctAns = myAns;
        System.out.println("" + this);
        return this;
    }

    @Override
    public String toString() {
        return format(this.question, this.correctAns);
    }
}

这样您就可以在链中调用 answer()，因为它 return 是对象本身 (this)。

如何连续调用一个方法两次？

How to call a method twice in a row?

java

methods

class