POJO在Scala中

Question

我有以下2个Java类

public class DataPoint<T> {

    public long timeStampMs;
    public T value;

    public DataPoint() {}

    public DataPoint(long timeStampMs, T value) {
        this.timeStampMs = timeStampMs;
        this.value = value;
    }

    public <R> DataPoint<R> withNewValue(R newValue){
        return new DataPoint(this.timeStampMs, newValue);
    }
    public KeyedDataPoint withKey(String key){
        return new KeyedDataPoint(key, this.timeStampMs, this.value);
    }
}

和

public class KeyedDataPoint<T> extends DataPoint<T>{

    public String key;

    public KeyedDataPoint() {}

    public KeyedDataPoint(String key, long timeStampMs, T value) {
        super(timeStampMs, value);
        this.key = key;
    }

    public <R> KeyedDataPoint<R> withNewValue(R newValue){
        return new KeyedDataPoint(this.key, this.timeStampMs, newValue);
    }

}

我需要翻译成Scala：

class DataPoint[T] (@BeanProperty val timeStampMs: Long, @BeanProperty val value: T) {
    def withNewValue[R](value: R): DataPoint[R] = new DataPoint[R](timeStampMs, value)
    def withKey(key: String): KeyedDataPoint[T] = new KeyedDataPoint(key, timeStampMs, value)
}

class KeyedDataPoint[T](@BeanProperty val key: String,
                        @BeanProperty override val timeStampMs: Long,
                        @BeanProperty override val value: T) extends DataPoint (timeStampMs, value) {
}

这些类需要符合POJO的条件，但是我不知道如何获得它。如果我提供一个无参数的主要构造函数，那么我不知道如何提供多个args辅助构造函数，反之亦然...如果我将主要构造函数留给几个参数，那么我将不知道如何提供无参数构造函数要求符合POJO。有帮助吗？

Answer 1

class Foo(s: String) {
    // alternative no-arg constructor (with different signature from primary)
    def this() {
        this("Default value from auxiliary constructor")
    }
}

请参考here

Answer 2

class KeyedDataPoint[T](@BeanProperty val key: String,
                        @BeanProperty override val timeStampMs: Long,
                        @BeanProperty override val value: Option[T]) extends DataPoint (timeStampMs, value) {
}  

class DataPoint[T] (@BeanProperty val timeStampMs: Long, @BeanProperty val value: Option[T]) {
    def this() {
      this(0, None);
    }  
    def withNewValue[R](value: Option[R]): DataPoint[R] = new DataPoint(timeStampMs, value)
    def withKey(key: String): KeyedDataPoint[T] = new KeyedDataPoint(key, timeStampMs, value)
}