Java 8 stream join and return multiple values

I'm porting a piece of code from .NET to Java and stumbled upon a scenario where I want to use stream to map & reduce.

class Content
{
  private String propA, propB, propC;
  Content(String a, String b, String c)
  {
    propA = a; propB = b; propC = c;
  }
  public String getA() { return propA; }
  public String getB() { return propB; }
  public String getC() { return propC; }
}

List<Content> contentList = new ArrayList();
contentList.add(new Content("A1", "B1", "C1"));
contentList.add(new Content("A2", "B2", "C2"));
contentList.add(new Content("A3", "B3", "C3"));

I want to write a function that can stream through the contents of contentlist and return a class with result

content { propA = "A1, A2, A3", propB = "B1, B2, B3", propC = "C1, C2, C3" }

I'm fairly new to Java so you might find some code that resembles more like C# than java