Homework
Java Chapter 5
5.1
1. What is the difference between a class and an object?
 A class is a software that describes the characteristics of similar objects and an
object is a run-time entity that contains data and responds to messages
2. What happens to an object’s memory storage when it is no longer referenced by a
variable?
 It is purged from the memory
3. List the three important characteristics of an object.
 Behavior
 State
 Identity
4. Describe the client-server relationship.
 The client knows only the interface of the server and sends messages to it
5. What is the interface of a class?
 The lists of methods supported by the server
5.2
1. What are mutators and accessors? Give examples.
 Mutators are methods that change an object’s state- s1.setName (“Bill”);
 Accessors access the object’s state to see if the mutator works- str =
s1.getName();
2. List two visibility modifiers and describe when they are used.
 private
 public
3. What is a constructor method?
 Methods that indicate how to initialize a new object
4. Why do we include a toString method with a new user-defined class?
 To obtain the object’s string representation
5. How can two variables refer to the same object? Give an example.
 By assigning a variable to a variable-s1 = s2
6. Explain the difference between a primitive type and a reference type and give an
example of each.
 Primitives are simple(int, double, char, etc.) while reference types are more
complex(all classes)
7. What is the null value?
 A value given to an object that has had its memory reclaimed by the garbage
collection of the computer
8. What is a null pointer exception? Give an example.
 When something is set to null and then tries to run but it can’t because the object
that is going to be used is set to null
 Ex- String str = null;
System.out.println(str.length());
9. How does a default constructor differ from other constructors?
 It has empty parameter lists
10. How does java handle the initialization of instance variables if no constructors are
provided?
 It provides a primitive default constructor
5.4
1. Explain the difference between formal parameters and actual parameters.
 Formal parameters-listed in a method’s definition
 Values passed to a method when it is invoked
2. How does java transmit data by means of parameters?
 The variable is stored in a formal parameter and then transferred to an instance
variable
3. Define a method sum. This method expects two integers as parameters and returns the
sum of the numbers ranging from the first integer to the second one.
 It assigns the method the result of adding two integers together and returns the
value
4. What is the purpose of local variables?
 Temporary working storage data in a method
5.5
1. What are the lifetimes of an instance variable, a local variable, and a parameter?
 Instance variable- all the methods in the defining class
 Local variable- The body of the method that declares it
 Parameter- The body of the method that declares it
2. What is shadowing? Give an example and describe the bad things that shadowing
might cause to happen in a program.
 Assigning a local variable the same name as a global variable
 Ex- public void setName(fishing)
{
this.fishing = fishing;
……
}
 It increases the chances of making a coding error
3.
a/ List the instance variable, parameters, and local variables in this code.
 Instance variable- int x & int y
 Parameters- private int a, b
 Local variables- int c, d
b/ Describe the scope of each variable or parameter.
 Int x, y- in the body of the method public void aMutator method
 Int a, b- in the body of the method public class SomeClass
 Int c, d- for the temporary storage of what they are assigned
c/ Describe the lifetime of each variable or parameter.
 Int x, y- for the duration of the public void aMutator method


Int a, b- for the durationg of public class SomeClass
Int c, d- for the temporary storage of what they are assigned