OnJava8-Examples/collections/ApplesAndOrangesWithoutGenerics.java

// collections/ApplesAndOrangesWithoutGenerics.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Simple collection use (suppressing compiler warnings)
// {ThrowsException}
import java.util.*;

class Apple {
  private static long counter;
  private final long id = counter++;
  public long id() { return id; }
}

class Orange {}

public class ApplesAndOrangesWithoutGenerics {
  @SuppressWarnings("unchecked")
  public static void main(String[] args) {
    ArrayList apples = new ArrayList();
    for(int i = 0; i < 3; i++)
      apples.add(new Apple());
    // No problem adding an Orange to apples:
    apples.add(new Orange());
    for(Object apple : apples) {
      ((Apple) apple).id();
      // Orange is detected only at runtime
    }
  }
}
/* Output:
___[ Error Output ]___
Exception in thread "main"
java.lang.ClassCastException: Orange cannot be cast to
Apple
        at ApplesAndOrangesWithoutGenerics.main(ApplesA
ndOrangesWithoutGenerics.java:23)
*/