Java Interfaces and UML

Implement the following class hierarchy on paper. You do not need to fill in the method bodies or include comments.

Solutions:

public interface Tossable
{
    void toss();
}

public abstract class Ball implements Tossable
{
    private String brandName;
    
    public Ball(String brandName)
    {
    }
    
    public String getBrandName()
    {
    }
    
    public abstract void toss();
    
    public abstract void bounce(); 
}

public class Baseball extends Ball
{

    public Baseball(String brandName)
    {
    }

    public void toss()
    {
    }

    public void bounce()
    {
    }

}

public class Football extends Ball
{

    public Football(String brandName)
    {      
    }
    
    public void toss()
    {
    }

    public void bounce()
    {
    }
}

public class Rock implements Tossable
{
    
    public void toss()
    {        
    }
    
}

Answer the following questions:

• How are abstract classes and interfaces the same?
• Both may include abstract method declarations that inheriting/implementing classes must override.
• Neither can be instantiated.
• Both can be used as types in variable declarations.
• How are abstract classes and interfaces different?
• Classes may inherit from at most one abstract class, while classes may implement any number of interfaces.
• Abstract classes may include method implementations, while interfaces may only include abstract method declarations.
• Fill in the following table with one of three values.
  • ✓ - An object of the indicated type could be stored in a variable of the indicated type.
  • X - An object of the indicated type could not be stored in a variable of the indicated type.
  • — - It is not possible to instantiate an object of the indicated type.

  		Variable Type
  		Throwable	Ball	Rock	Baseball	Football
  Object Type	Throwable	—	—	—	—	—
  	Ball	—	—	—	—	—
  	Rock	✓	X	✓	X	X
  	Baseball	✓	✓	X	✓	X
  	Football	✓	✓	X	X	✓