Chapter 4 Java
True or False: Every Java class has at least 1 constructor
True: if you don't define one the compiler gives a no-args constructor that initializes all instance variables to default values (0 for #s, null for objects, false for boolean)
True or False: A class may have more than one constructor.
True; A class may have many different constructors.
True or False: The programmer gives names to objects in his program.
True; A programmer may give his objects any name.
What are accessor methods/accessors/getters?
public methods that return the values of an object's private fields so that an object of a different class can access those values
Several compiled java classes may be collected in one ________
.jar file
What are three benefits of encapsulation?
1. The fields of a class can be made read-only or write-only. 2. A class can have total control over what is stored in its field. 3. The users of a class do not know how the class stores its data. A class can change the data type of a field and users of the class do not need to change any of their code.
What is inheritance?
Can create a new class by extending an existing one.
True or False: A Java program is allowed to create only one object of each class.
False; An infinite number of objects may exist.
True or False: The import statement tells the compiler which other classes use this class.
False; It tells the compiler where it can find classes used by this class.
True or False: Every class has a method called "main".
False; No, you can have classes with different methods.
True or False: A subclass inherits all those constructors of its superclass that are not defined explicitly in the subclass.
False; constructors aren't inherited.
In Java every class extends the library class _______ by default.
Object
True or False: Fields of a class are usually declared "private".
True
A subclass does not inherit ________
constructors
What's a CRC card?
index card that gives basic, informal description of a class: name, key responsibilities of objects, collaborators (other classes this class depends on)
If void is in a method's header it means that ________
the method does not return a value Ex: main
What does it mean when a method is declared static?
That method belongs to a class as a whole, not to any particular object of that class.
What is the IS-A relationship between objects?
an object of a subclass IS-A object of its superclass
What are setters/modifiers?
methods that set the values of private fields
A subclass inherits all the ______ & _______ of its superclass.
methods, fields
True or False: The name of a class in Java must be the same as the name of its source file. (excluding the extension ".java")
True; A class cannot have a different name than the source file.
True or False: A Java program may have as many classes as necessary.
True; You can have an infinite number of classes in a Java program.
True or False: An object has to be created before it can be used.
True; You can't use something that doesn't exist.
True or False: The names of classes are case-sensitive.
True; You must use the correct case when naming classes.
True or False: A subclass inherits all the fields and public methods of its superclass.
True; a subclass does inherit all the fields and public methods.