问题

Sure, here's the translated Java code for your Scala code:

import java.util.HashMap;
import java.util.Map;
import java.util.Optional;

class Writer {
    private static Map<String, String> options = new HashMap<>();

    public static Optional<String> a() {
        return Optional.ofNullable(options.get("a"));
    }

    public static Optional<String> b() {
        return Optional.ofNullable(options.get("b"));
    }

    public static Optional<String> c() {
        return Optional.ofNullable(options.get("c"));
    }

    public static Writer option(String key, String value) {
        options.put(key, value);
        return Writer.this;
    }

    public static void write() {
        System.out.println(a().orElse("Z"));
        System.out.println(b().orElse("Z"));
        System.out.println(c().orElse("Z"));
    }
}

public class Run {
    public static void main(String[] args) {
        Writer.write();

        Writer.option("a", "A")
              .option("b", "B")
              .option("c", "C")
              .write();
    }
}

Please note that the translation from Scala to Java might not be a straightforward one-to-one mapping, as the languages have different syntax and features. In this translation, I've used Optional for handling the absence of values, and I've adjusted the method and field access to Java conventions.

object Writer {
val options = new scala.collection.mutable.HashMap[String, String]
def a: Option[String] = options.get("a")
def b: Option[String] = options.get("b")
def c: Option[String] = options.get("c")
def option(key: String, value: String): Writer.type = {
options += (key -> value)
this
}
def write() ={
println(a.getOrElse("Z"))
println(b.getOrElse("Z"))
println(c.getOrElse("Z"))
}
}

object Run {
def main(args: Array[String]): Unit = {
Writer
.write()
Writer
.option("a", "A")
.option("b", "B")
.option("c", "C")
.write()
}
}

答案1

得分: 2

Scala的对象就像Java中的单例对象：

import scala.collection.mutable.HashMap

object Writer {
  private val options: HashMap[String, String] = new HashMap[String, String]()

  def a(): Option[String] = {
    options.get("a")
  }

  def b(): Option[String] = {
    options.get("b")
  }

  def c(): Option[String] = {
    options.get("c")
  }

  def option(key: String, value: String): this.type = {
    options(key) = value
    this
  }

  def write(): Unit = {
    println(a().getOrElse("Z"))
    println(b().getOrElse("Z"))
    println(c().getOrElse("Z"))
  }

  def main(args: Array[String]): Unit = {
    Writer
      .option("a", "A")
      .option("b", "B")
      .option("c", "C")
      .write()

    Writer.write() // 与上面的输出相同
  }
}

请注意，Scala中的单例对象使用object关键字定义，其内部成员和方法可以通过点符号访问，类似于Java中的静态成员和方法。

import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
public class Writer {
private Writer(){}
private static Writer instance;
public static Writer getInstance() {
if (instance == null) {
instance = new Writer();
}
return instance;
}
public Map<String, String> options = new HashMap<>();
public Optional<String> a() {
return Optional.ofNullable(options.get("a"));
}
public Optional<String> b() {
return Optional.ofNullable(options.get("b"));
}
public Optional<String> c() {
return Optional.ofNullable(options.get("c"));
}
public Writer option(String key, String value) {
options.put(key, value);
return this;
}
public void write() {
System.out.println(a().orElse("Z"));
System.out.println(b().orElse("Z"));
System.out.println(c().orElse("Z"));
}
public static void main(String[] args) {
Writer.getInstance()
.option("a", "A")
.option("b", "B")
.option("c", "C")
.write();
Writer.getInstance().write(); // same output as above
}
}