Inheritance

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What we’ll cover

Class inheritance

Object Class

Object Methods

Super and Final Keywords

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Terminology

• Subclass - a class that inherits some of its behavior from another class
• Superclass - the class from which a subclass inherits
• Parent/child class - synonyms for superclass and subclass; slightly imprecise Note: the parent/child/ancestor/descendant metaphor is very common, despite being somewhat misleading.

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Class inheritance

• classes can inherit the interfaces of classes and extend their feature set
• this is achieved with the extends keyword
• If B extends A then B has all of A’s public and protected members and methods
• package access only within the same package

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Inheritance is an “is a” or “is like a” relationship

• An SUV is a Vehicle
• A corgi is a Dog

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Example: SUV

public class Vehicle{
  public void start(){...}
}

class SUV extends Vehicle{
  public void drive(){
    start();
    ...
  }
}

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Example: Corgi

class Dog{public void wag(){...}}
public class Corgi extends Dog{
  public static void main(String[] args){
    Corgi bucket = new Corgi();
    bucket.wag();
  }
}

Full example

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Upcasting

• Objects can be treated as instances of any superclass in the class hierarchy

public class App{
 public static void main(String[] args){
  Dog pembroke = new Corgi();
  pembroke.wag();
  }
}