DoublePointer.java

class DoublePointer {
  String s;
  public DoublePointer(String s){
    this.s = s;
  }
}

public class IdentitySwitch {
  public static void main(String[] args) {
    DoublePointer dp = new DoublePointer("unchanged");
    System.out.println(dp.s);
    foo(dp.s);
    System.out.println(dp.s);
  }
  
  public void foo(DoublePointer dp) {
    dp.s = "changed"
  }
}