Scala 和java

1、scala语法中将java的接口当作类去使用

@FunctionalInterface
@Public
public interface ReduceFunction extends Function, Serializable {
    T reduce(T var1, T var2) throws Exception;
}

class MyReduceFunction extends ReduceFunction[SensorReading] {
  override def reduce(t: SensorReading, t1: SensorReading): SensorReading = {
    SensorReading(t.id, t1.timestamp, t.temperature.min(t1.temperature))
  }
}


ReduceFunction的接口需要继承才能使用

@PublicEvolving
public interface ValueState extends State {
    T value() throws IOException;

    void update(T var1) throws IOException;
}


将ValueState作为类的类型使用
  var lastValueState: ValueState[Double] = _

2、Unit代表返回为空

  override def open(parameters: Configuration): Unit = {
    lastValueState = getRuntimeContext.getState(new ValueStateDescriptor[Double]("tempState", classOf[Double]))
  }