Covert short code scala to java

Question
1

please help me , convert short code scala to java , i’m newbie in scala

protected def readBytes: Array[Byte] = {
val n = read
(0 until n).foldLeft(new Array[Byte](n)) {
    case (a, index) => 
      a(index) = read
      a
  }
}
1 Like
2

I’m sorry, but I don’t understand what you are asking help doing. Can you clarify?

3

You didn’t provide a definition of read, I’m assuming it is a method that returns a Byte.

The code looks like an overly convoluted way to create an Array and fill it with values. Unless I’m missing something, it does the same as:

protected def readBytes: Array[Byte] = {

val n = read

val bytes = new Array(n)

var index = 0

while(index < n) {

bytes(index) = read

index += 1

}

bytes

}

My Java is a bit rusty, but I think you want to do something like:

protected byte[] readBytes {

int n = read()

int index = 0

byte[] bytes = new byte[n]

while(index < n) {

bytes[index] = read()

index++

}

return bytes

**}

4

One way to convert Scala code to Java is to compile it and then use a Java decompiler

5

Interesting. Have you done that before on real code? I’m curious about the quality of the resulting Java code. Is it quality code, or is it a mess? Thanks.

6

[…] Is it quality code, or is it a mess? […]

I’d say that mostly depends on the decompiler used. But this method is as well demonstrated in “Progamming in Scala”.

7

Not sure if literal conversion is needed but here are simple implementations:

Java:

        Scanner source = null; // replace this with proper source
        byte[] array = new byte[source.nextInt()];
        for (int i = 0; i < array.length; i++) {
            array[i] = source.nextByte();
        }

Scala:

    val source: Scanner = null // replace this with proper source
    val array = Array.fill(source.nextInt)(source.nextByte)
8

Well here’s what I got from IntelliJ…

Original code:

class TestRead {
  def read: Byte = ???
  protected def readBytes: Array[Byte] = {
    val n = read
    (0 until n).foldLeft(new Array[Byte](n)) {
      case (a, index) =>
        a(index) = read
        a
    }
  }
}

For some reason I couldn’t see the class files in the project explorer so I had to open it in the OS file browser and drag it onto the IntelliJ window. Then it showed the usual decompiled scala outline:

package chesednow.people.views
class TestRead() extends scala.AnyRef {
  def read : scala.Byte = { /* compiled code */ }
  protected def readBytes : scala.Array[scala.Byte] = { /* compiled code */ }
}

From there I was able to right click and select Decompile Scala to Java. The final result is this:

//decompiled from TestRead.class
package chesednow.people.views;

import java.lang.invoke.SerializedLambda;
import scala.MatchError;
import scala.Tuple2;
import scala.Predef.;
import scala.reflect.ScalaSignature;
import scala.runtime.BoxesRunTime;

@ScalaSignature(
   bytes = "\u0006\u0001\u00052A\u0001B\u0003\u0001\u0019!)1\u0003\u0001C\u0001)!)q\u0003\u0001C\u00011!)A\u0004\u0001C\t;\tAA+Z:u%\u0016\fGM\u0003\u0002\u0007\u000f\u0005)a/[3xg*\u0011\u0001\"C\u0001\u0007a\u0016|\u0007\u000f\\3\u000b\u0003)\t\u0011b\u00195fg\u0016$gn\\<\u0004\u0001M\u0011\u0001!\u0004\t\u0003\u001dEi\u0011a\u0004\u0006\u0002!\u0005)1oY1mC&\u0011!c\u0004\u0002\u0007\u0003:L(+\u001a4\u0002\rqJg.\u001b;?)\u0005)\u0002C\u0001\f\u0001\u001b\u0005)\u0011\u0001\u0002:fC\u0012,\u0012!\u0007\t\u0003\u001diI!aG\b\u0003\t\tKH/Z\u0001\ne\u0016\fGMQ=uKN,\u0012A\b\t\u0004\u001d}I\u0012B\u0001\u0011\u0010\u0005\u0015\t%O]1z\u0001"
)
public class TestRead {
   public byte read() {
      throw .MODULE$.$qmark$qmark$qmark();
   }

   public byte[] readBytes() {
      byte n = this.read();
      return (byte[])scala.runtime.RichInt..MODULE$.until$extension0(.MODULE$.intWrapper(0), n).foldLeft(new byte[n], (x0$1, x1$1) -> {
         return $anonfun$readBytes$1(this, x0$1, BoxesRunTime.unboxToInt(x1$1));
      });
   }

   // $FF: synthetic method
   public static final byte[] $anonfun$readBytes$1(final TestRead $this, final byte[] x0$1, final int x1$1) {
      Tuple2 var4 = new Tuple2(x0$1, BoxesRunTime.boxToInteger(x1$1));
      if (var4 != null) {
         byte[] a = (byte[])var4._1();
         int index = var4._2$mcI$sp();
         a[index] = $this.read();
         return a;
      } else {
         throw new MatchError(var4);
      }
   }

   // $FF: synthetic method
   private static Object $deserializeLambda$(SerializedLambda var0) {
      return var0.lambdaDeserialize<invokedynamic>(var0);
   }
}
9

thanks it work for me :smiley: