Java instances - instanceOf keyword usage

/*
 author by w3cschool.cc
 Main.java
 */import java.util.ArrayList;import java.util.Vector;public class Main {public static void main(String[] args) {
   Object testObject = new ArrayList();
      displayObjectClass(testObject);
   }
   public static void displayObjectClass(Object o) {
      if (o instanceof Vector)
      System.out.println("对象是 java.util.Vector 类的实例");
      else if (o instanceof ArrayList)
      System.out.println("对象是 java.util.ArrayList 类的实例");
      else
      System.out.println("对象是 " + o.getClass() + " 类的实例");
   }}

对象是 java.util.ArrayList 类的实例