Chapter 7

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Chapter 7

Inheritance

This activity contains 15 questions.

"class Aggregate" is incorrect. Choose the correct line so that this program prints:

Granite: weight=25.0 value=4 numKind=7

public class Inherit {

	class Stone {
		protected float weight = 13;
		protected int   value  = 4;
	}

	class Aggregate {
		protected int numKind;
	}

	class Granite extends Aggregate {
		Granite() {
			weight = 25; numKind = 7;
		}
		public String toString() {
			return "Granite: weight=" 
			   + weight + " value=" 
			   + value  + " numKind="
			   + numKind;
		}
	}

	Inherit() {
		Granite g = new Granite();
		System.out.println(g);
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

Incorrect code... Just changing the class declaration for Aggregate won't fix itclass Aggregate extends Object {class Aggregate extends Granite {class Aggregate extends Stone {

Say you want to access a variable or method in a base class, from a derived class, but it is marked private. Which statement is true?

No problem. Since the derived class inherits base class variables and methods, just use the name of the variable or methodYou'd have to create an accessor or mutator in order to access the variable (or method) - there is no other way to access itNo problem. Just use super to access it from the derived classNo problem. Just mark it static and it will become visible

What can you say about this code?

class Speaker {
	void speak() {
		System.out.println("Woof, woof!");
	}
	int age = 3;
}

public class Inherit {

	class Dog extends Speaker {
		protected String name;
	}

	class MyDog extends Dog {
		MyDog() { name = "Lassie"; }
		public void speak() {
			System.out.println(
			  "My name is " + name);
			System.out.println(
			  "My age is " + age);
			}
		}

	Inherit() { new MyDog().speak(); }

	public static void main(String[] args) {
		new Inherit();
	}
}

MyDog should extend Speaker, not Dog.The code prints: Woof, woof!It prints two lines:
My name is Lassie
My age is 3Syntax error: This code won't compile or run

What is printed?

public class Inherit {

	class Stone {
		protected float weight = 13;
		protected int   value  = 4;
		public String toString() {
			return "Stone";
		}
	}

	class Granite extends Stone {
		Granite() { weight = 25; }
		public String toString() {
			return "Granite: weight=" 
			   + weight + " value=" + value;
		}
	}

	class Mica extends Stone {
		Mica() { value = 7; }
		public String toString() {
			return "Mica:    weight=" 
			   + weight + " value=" + value;
		}
	}

	Inherit() {
		Granite g = new Granite();
		Mica    q = new Mica();
		System.out.println(g);
		System.out.println(q);
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

Granite: weight=25.0 value=4
Mica: weight=13.0 value=4Granite: weight=13.0 value=4
Mica: weight=13.0 value=7Granite: weight=13.0 value=4
Mica: weight=13.0 value=4Granite: weight=25.0 value=4
Mica: weight=13.0 value=7

What is printed?

class Speaker {
	void speak() {
		System.out.println("Growl!");
	}
}

public class Inherit {

	class Dog extends Speaker {
		public void speak() {
			System.out.println("Woof!");
		}
	}

	class Cat extends Speaker {
		public void speak() {
			System.out.println("Meow!");
		}
	}

	Inherit() {
		Speaker c = new Dog();
		Speaker d = new Cat();
		c.speak();
		d.speak();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

Meow!
Woof! Meow!
Meow! Woof!
Woof! Woof!
Meow!

What is printed?

public class Inherit {

	class Animal {
		private int numEyes = 1;
		private int numFeet = 2;

		Animal() { }

		Animal(int numEyes) {
			this.numEyes = numEyes;
		}

		Animal(int numEyes, int numFeet) {
			this(numEyes);
			this.numFeet = numFeet;
		}

		public String toString() {
			return
				" numEyes=" + numEyes +
				" numFeet=" + numFeet;
		}
	}

	Inherit() {
		Animal a1 = new Animal();
		Animal a2 = new Animal(5);
		Animal a3 = new Animal(4, 6);
		System.out.println(a1);
		System.out.println(a2);
		System.out.println(a3);
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

numEyes=1 numFeet=2
numEyes=1 numFeet=2
numEyes=1 numFeet=2numEyes=1 numFeet=2
numEyes=4 numFeet=6
numEyes=4 numFeet=6numEyes=1 numFeet=2
numEyes=5 numFeet=2
numEyes=4 numFeet=6numEyes=5 numFeet=2
numEyes=5 numFeet=2
numEyes=4 numFeet=6

What is printed?

public class Inherit {

	class Speaker {
		public void speak() {
			System.out.println("Growl!");
		}
	}

	class Cat extends Speaker {
		public void speak() {
			System.out.println("Woof!");
		}
	}

	class Dog extends Speaker {
		public void speak() {
			System.out.println("Meow!");
		}
	}

	Inherit() {
		Speaker d = new Dog();
		Speaker c = new Cat();
		d.speak();
		c.speak();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

Woof!
Woof! Woof!
Meow! Meow!
Woof! Meow!
Meow!

What is printed?

public class Inherit {

	class Stone {
		protected float weight = 13;
		protected int   value  = 4;
		public String toString() {
			return "Stone";
		}
	}

	class Granite extends Stone {
		private int value = 9;
		public String toString() {
			return "Granite: weight=" 
			   + weight + " value=" + value;
		}
		public void report() {
			System.out.println(
				"Stone's value=" 
				+ super.value);
		}
	}

	Inherit() {
		Granite g = new Granite();
		System.out.println(g);
		g.report();
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

Granite: weight=13.0 value=4
Stone's value=4Granite: weight=9 value=9
Stone's value=4Granite: weight=13.0 value=9
Stone's value=4Granite: weight=13.0 value=9
Stone's value=9

What is printed?

public class Inherit {

	class Stone {
		Stone() { }
		Stone(int value) {
			this.value = value;
		}
		protected float weight = 13;
		protected int value = 4;
		public String toString() {
			return "Stone";
		}
	}

	class Granite extends Stone {
		Granite() { weight = 25; }
		Granite(int value) {
			super(7);  weight = 19;
		}
		public String toString() {
			return "Granite: weight=" 
			   + weight + " value=" + value;
		}
	}

	Inherit() {
		Granite g2 = new Granite();
		Granite g3 = new Granite(7);
		System.out.println(g2);
		System.out.println(g3);
	}

	public static void main(String[] args) {
		new Inherit();
	}
}

Granite: weight=25.0 value=4
Granite: weight=25.0 value=4Granite: weight=25.0 value=4
Granite: weight=19.0 value=4Granite: weight=25.0 value=4
Granite: weight=25.0 value=7Granite: weight=25.0 value=4
Granite: weight=19.0 value=7

What statement(s) are true?

static variables and methods always are inherited, even if they're marked private
static variables and methods only are inherited if no public, protected, or private modifier is used for them
static variables and methods only are inherited if they're not declared private
static variables and methods follow different rules regarding their visibility in inheritance situations

Statements (b) and (c) are trueOnly statement (c) is trueStatements (b), (c) and (d) are all true.Statements (a) and (c) are true

When does an instance variable (or a method) have package (or friendly) access?

An instance variable (or method) has package access when you omit all modifiers, except, perhaps staticAn instance variable (or method) has package access when you use any of the modifiers, public, protected, or privateAn instance variable (or method) has package access when you use the protected modifierAn instance variable (or method) has package access when you use the public modifier

Which statement(s) are true?

You can use super to access a base method that has been overridden
You can use this to access a base method that has been overridden
You can use super to access a private base method
You can use this to access a private base method

Only statement (b) is trueOnly statement (a) is trueOnly statements (a) and (c) are trueOnly statements (a) and (b) are true

Which statements are true?

Friendly access is the same as default access
Package access is the same as friendly access
Private variables and methods can be inherited by derived classes
Protected methods can be inherited by derived classes, but no protected variables can be
A private method can be accessed outside its class, so long as the class itself is declared to be public

All the statements are trueTrue statements: (a), (b), (c), and (e).True statements: (a) and (b)True statements: (a), (b), and (c).

Which statements are true?

Overriding is just another term for overloading
Overloading only can be done within an inheritance structure
Overriding only can be done within an inheritance structure
You can overload a constructor
You can override a constructor

All the statements are trueOnly statement (d) is trueOnly statements (c) and (d) are trueTrue statements: (b), (c), (d), and (e)

Why should you use the getClass method within a definition of an equals method rather than instanceOf?

getClass should be used because it works correctly in cases where one argument is derived from the otherUsing getClass is more efficient at runtime than instanceOfThere really isn't any strong reason for preferring getClass to instanceOf - it's a matter of taste or styleThat's backwards! You should use instanceOf, not getClass when overriding equals

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Chapter 7

Say you want to access a variable or method in a base class, from a derived class, but it is marked private. Which statement is true?

When does an instance variable (or a method) have package (or friendly) access?

Which statements are true? Overriding is just another term for overloading Overloading only can be done within an inheritance structure Overriding only can be done within an inheritance structure You can overload a constructor You can override a constructor

Why should you use the getClass method within a definition of an equals method rather than instanceOf?

Which statements are true?

Overriding is just another term for overloading
Overloading only can be done within an inheritance structure
Overriding only can be done within an inheritance structure
You can overload a constructor
You can override a constructor