Unit 2

What is an object in Java?

• An object is a template for how to make new programs in Java.

• An object is something that contains both state and behavior.

• An object is a single part of a computer program.

• An object is a list of variables.

Which of the following best describes the relationship between a class and an object?

• A class definition specifies the attributes and behavior of every object that will be made.

• An object definition specifies the attributes and behavior of every class that will be made.

• A class specifies the attributes and behaviors for exactly one object.

• Every object can choose which attributes and behavior it wants to keep from the class definition.

Every class definition has each of the following EXCEPT

• A name

• Defined attributes

• Defined behaviors to manipulate the state of the objects

• Defined objects as copies of the class

public class Pineapple

{

private boolean isRipe;

private String color;

private double weight;

// Rest of class goes here

}

• Every Pineapple object will be yellow

• Every Pineapple object must choose which attributes it wants.

• Every Pineapple object will have the same attributes.

• It is impossible to know what attributes the Pineapple objects will have since the attributes are not listed here.

What is a constructor in Java?

• A constructor is something that holds the private state of an instance.

• A constructor allows us to create a new instance of a class, usually initializing instance variables.

• A constructor is a method with instructions on how to use a class.

• A constructor is a syntax rule in Java for placing curly brackets.

public class Card

{

private String suit;

private int value; //13 values for each suit in deck (0 to 12)

public Card (String cardSuit, int cardValue)

{

/* implementation */

}

// Rest of the class goes here

}

• cardSuit = suit;

  cardValue = value;

• Card = new Card (cardSuit, cardValue);

• suit = cardSuit;

  value = cardValue;

• suit = "Hearts";

  value = 3;

/**

* The Shark class describes a shark.

*

* Every shark has a region where it lives and an age.

*

*/

public class Shark

{

// Attributes

private String habitat;

private int age;

public Shark(String region, int sharkAge)

{

habitat = region;

age = sharkAge;

}

}

• habitat

• String

• Shark

• sharkAge

What is the purpose of overloading a class’ constructor?

• It allows the user to create more than one object from the class.

• It allows the user to make different types of objects from a single class type.

• It allows the user to set the values of different combinations of the instance variables when the object is created.

• It allows the user to call different constructors for the same object to initialize different instance variables.

Which of the following is NOT part of the constructor signature?

• Which instance variables are initialized

• The parameter types

• The order of the parameters

• The name of the constructor

Which of the following is NOT a valid way to overload this constructor? For brevity, only the signature is given.

Pineapple(String color)

• Pineapple()

• Pineapple(String color, int age)

• Pineapple(int age, String species)

• FancyPineapple(String color, int age)