An example of the utility of private[this]

example.scala

class Regular {
  private var i = 0
  
  def inc() {
    i += 1
  }

  def get = i
}

class Special {
  private[this] var i = 0
  
  def inc() {
    i += 1
  }

  def get = i
}

Regular.java

//decompiled with JD-GUI
import scala.ScalaObject;
import scala.reflect.ScalaSignature;

@ScalaSignature(bytes="\006\00192A!\001\002\001\013\t9!+Z4vY\006\024(\"A\002\002\017q*W\016\035;z}\r\0011c\001\001\007\035A\021q\001D\007\002\021)\021\021BC\001\005Y\006twMC\001\f\003\021Q\027M^1\n\0055A!AB(cU\026\034G\017\005\002\020%5\t\001CC\001\022\003\025\0318-\0317b\023\t\031\002CA\006TG\006d\027m\0242kK\016$\b\"B\013\001\t\0031\022A\002\037j]&$h\bF\001\030!\tA\002!D\001\003\021\035Q\002\0011A\005\nm\t\021![\013\0029A\021q\"H\005\003=A\0211!\0238u\021\035\001\003\0011A\005\n\005\nQ![0%KF$\"AI\023\021\005=\031\023B\001\023\021\005\021)f.\033;\t\017\031z\022\021!a\0019\005\031\001\020J\031\t\r!\002\001\025)\003\035\003\tI\007\005C\003+\001\021\0051&A\002j]\016$\022A\t\005\006[\001!\taG\001\004O\026$\b")
public class Regular
  implements ScalaObject
{
  private int i = 0;

  private int i() { return this.i; } 
  private void i_$eq(int paramInt) { this.i = paramInt; }

  public void inc() {
    i_$eq(i() + 1);
  }
  public int get() {
    return i();
  }
}

Regular.javap

Compiled from "example.scala"
public class Regular extends java.lang.Object implements scala.ScalaObject{
public void inc();
  Code:
   0:	aload_0
   1:	aload_0
   2:	invokespecial	#17; //Method i:()I
   5:	iconst_1
   6:	iadd
   7:	invokespecial	#19; //Method i_$eq:(I)V
   10:	return

public int get();
  Code:
   0:	aload_0
   1:	invokespecial	#17; //Method i:()I
   4:	ireturn

public Regular();
  Code:
   0:	aload_0
   1:	invokespecial	#25; //Method java/lang/Object."<init>":()V
   4:	aload_0
   5:	iconst_0
   6:	putfield	#11; //Field i:I
   9:	return

}

Special.java

// decompiled with JD-GUI
import scala.ScalaObject;
import scala.reflect.ScalaSignature;

@ScalaSignature(bytes="\006\001\0352A!\001\002\001\013\t91\013]3dS\006d'\"A\002\002\017q*W\016\035;z}\r\0011c\001\001\007\035A\021q\001D\007\002\021)\021\021BC\001\005Y\006twMC\001\f\003\021Q\027M^1\n\0055A!AB(cU\026\034G\017\005\002\020%5\t\001CC\001\022\003\025\0318-\0317b\023\t\031\002CA\006TG\006d\027m\0242kK\016$\b\"B\013\001\t\0031\022A\002\037j]&$h\bF\001\030!\tA\002!D\001\003\021\031Q\002\001)Q\0057\005\t\021\016\005\002\0209%\021Q\004\005\002\004\023:$\b\"B\020\001\t\003\001\023aA5oGR\t\021\005\005\002\020E%\0211\005\005\002\005+:LG\017C\003&\001\021\005a%A\002hKR,\022a\007")
public class Special
  implements ScalaObject
{
  private int i = 0;

  public void inc() {
    this.i += 1;
  }
  public int get() {
    return this.i;
  }
}

Special.javap

Compiled from "example.scala"
public class Special extends java.lang.Object implements scala.ScalaObject{
public void inc();
  Code:
   0:	aload_0
   1:	aload_0
   2:	getfield	#12; //Field i:I
   5:	iconst_1
   6:	iadd
   7:	putfield	#12; //Field i:I
   10:	return

public int get();
  Code:
   0:	aload_0
   1:	getfield	#12; //Field i:I
   4:	ireturn

public Special();
  Code:
   0:	aload_0
   1:	invokespecial	#19; //Method java/lang/Object."<init>":()V
   4:	aload_0
   5:	iconst_0
   6:	putfield	#12; //Field i:I
   9:	return

}