lecture 4

Animal foo = new Dog(); // ok

override heiachy

dog[] is animal[]

final no sub class

String is final

Dog dog = new Animal() // cannot go up
Dog dog = new GoldenRetriver // ok
GoldenRetriver cc = new Dog() // no
Goldenretriver goldenrever = (Goldenretrive) dog // depends on if dog is GoldenRetriver

Abstract class

super

invoke super constructor

 public class Cat extends Animal {
      @Override protected String makeNoise(){
      
  }
}

• attempt to assign weaker access privileges' was public (cannot override it in animal)

@Override public String makeNoise(){
    return "meow"
}

Abstract

 public abstract class Animal{
   public abstract String makeNoise();
}

Abstract class you might not need the implementation

Object class

getClass()  
 // returns the Class class instance
hashcode()  
// a hash code value for this object

private final String name
@Override public boolean equals(Object obj) {
      if (this == obj) {
          return true;
      }
      if ((obj == null ) || (getClass() != obj.getClass()) {
         return false;
      }
      // for every propery under consideration for equality, check  
        Dog that = (Dog) obj
       return (nam ==  null ? that.name == null : name.equals(that.name));
}

@Override public int hashCode() {
      int result = this.id == null ? 0 : id.hashCode();
      result = 31 (prime number) * result + (dateTime == null ? 0 : dateTime.hashCode());
      return result;
      //return (this.name == null ? 0 : this.name.hashCode());
}

if equals gethashCode must be the same