Java/Language Basics/Intanceof

Finding Out of what Class an Object is Instantiated

 
import java.util.ArrayList;
import java.util.Vector;
public class Main {
  public static void main(String[] args) {
    Object testObject = new Vector();
    if (testObject instanceof Vector)
      System.out.println("Object was an instance of the class java.util.Vector");
    else if (testObject instanceof ArrayList)
      System.out.println("Object was an instance of the class java.util.ArrayList");
    else
      System.out.println("Object was an instance of the " + testObject.getClass());
  }
}
//Object was an instance of the class java.util.Vector

Get a class of an object

 
 
import java.util.ArrayList;
import java.util.List;
public class Main {
  public static void main(String[] args) {
    Person p = new Person("A");
    Animal a = new Animal("B");
    Thing t = new Thing("C");
    String text = "hello";
    Integer number = 1000;
    List<Object> list = new ArrayList<Object>();
    list.add(p);
    list.add(a);
    list.add(t);
    list.add(text);
    list.add(number);
    for (int i = 0; i < list.size(); i++) {
      Object o = list.get(i);
      if (o instanceof Person) {
        System.out.println("My name is " + ((Person) o).getName());
      } else if (o instanceof Animal) {
        System.out.println("I live in " + ((Animal) o).getHabitat());
      } else if (o instanceof Thing) {
        System.out.println("My color is " + ((Thing) o).getColor());
      } else if (o instanceof String) {
        System.out.println("My text is " + o.toString());
      } else if (o instanceof Integer) {
        System.out.println("My value is " + ((Integer) o));
      }
    }
  }
}
class Person {
  private String name;
  public Person(String name) {
    this.name = name;
  }
  public String getName() {
    return name;
  }
}
class Animal {
  private String habitat;
  public Animal(String habitat) {
    this.habitat = habitat;
  }
  public String getHabitat() {
    return habitat;
  }
}
class Thing {
  private String color;
  public Thing(String color) {
    this.color = color;
  }
  public String getColor() {
    return color;
  }
}

The difference between instanceof and class

 
// : c10:FamilyVsExactType.java
// The difference between instanceof and class
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class Base {
}
class Derived extends Base {
}
public class FamilyVsExactType {
  static void test(Object x) {
    System.out.println("Testing x of type " + x.getClass());
    System.out.println("x instanceof Base " + (x instanceof Base));
    System.out.println("x instanceof Derived " + (x instanceof Derived));
    System.out.println("Base.isInstance(x) " + Base.class.isInstance(x));
    System.out.println("Derived.isInstance(x) "
        + Derived.class.isInstance(x));
    System.out.println("x.getClass() == Base.class "
        + (x.getClass() == Base.class));
    System.out.println("x.getClass() == Derived.class "
        + (x.getClass() == Derived.class));
    System.out.println("x.getClass().equals(Base.class)) "
        + (x.getClass().equals(Base.class)));
    System.out.println("x.getClass().equals(Derived.class)) "
        + (x.getClass().equals(Derived.class)));
  }
  public static void main(String[] args) {
    test(new Base());
    test(new Derived());
  }
} ///:~