java - 如何使java流畅界面中的方法首先弹出？

Question

这是我第一次提问，如果我弄乱了一些东西，我很抱歉。我有一个任务是使用 Java 流畅的接口(interface)来实现邮件。我必须有字段:发件人、收件人、主题。

问题是，我无法让“From”作为第一个且唯一的出现。例子:MailBuilder 构建器 = new MailBuilder();builder.from("Stiliyan").to("Alexander").subject("欢迎加入");

但是当我输入第一个点“.”时他们都出现了。 (例如 builder.to("a").from("b")..)

简而言之:builder.(此处必须仅出现“from”).to(“无忧”)...”

Here is MailBuilder.java

So here after "." must appear ONLY from method

Answer 1

那么每个构建器方法的声明返回类型不能相同。不过，您仍然可以返回相同的构建器实例。例如:

interface IFromBuilder {
    IToBuilder from(String from);
}

interface IToBuilder {
    IMailBuilder to(String to);
}

interface IMailBuilder {
    Mail build();
}

class MailBuilder implements IFromBuilder, IToBuilder, IMailBuilder {

    private String from;
    private String to;

    @Override
    public IToBuilder from(String from) {
        this.from = from;
        return this;
    }

    @Override
    public IMailBuilder to(String to) {
        this.to = to;
        return this;
    }

    @Override
    public Mail build() {
        return new Mail(from, to);
    }
}

class Mail {
    private final String from;
    private final String to;

    public Mail(String from, String to) {
        this.from = from;
        this.to = to;
    }

    public static IFromBuilder newBuilder() {
        return new MailBuilder();
    }
}


public class Demo {
    public static void main(String[] args) {
        Mail mail = Mail.newBuilder().from("sender@a.com").to("receiver@b.com").build();
    }
}