Objectives

• Further understanding of object oriented programming

Declaring new types

Class declarations are one of the ways of defining new types in Java. For this laboratory, we will create two classes that both represent time values for a 24 hours period. The valid operations are as follows.

• int getHours(): returns the number of hours
• int getMinutes(): returns the number of minutes
• int getSeconds(): returns the number of seconds
• String toString(): returns a String representation
• boolean equals(Time other): returns true if and only if other designates an object that has the same content as this one
• void increase(): increases this time by one second
• Time plus(Time other): returns a new time object who value represents the sum of this time and that of other
• boolean before(Time other): returns true if and only if this time object represents a time value that is before that of other

Note: at the end of this laboratory, you will submit the content of a directory called l3_123456, where 123456 has been substituted by your student id. You might as well create the directory now and save all the files that you will be creating into that directory.

1 Time1

Consult the declaration of the class Time1.

• Time1.java

Modify the declaration of the class Time1 and implement the following two methods.

• Time1 plus(Time1 other): returns a new time object who value represents the sum of this time and that of other
• boolean before(Time1 other): returns true if and only if this time object represents a time value that is before that of other

Create a new class called Utils1 containing the following two class methods:

• boolean isIncreasing(Time1[] ts): returns true if and only if the elements of the array designated by the formal parameter ts are in increasing order of time.
• void main(String[] args):
  1. The method obtains 3 integer values from the command line (see Laboratory 1)
  2. It declares a reference variable t of type Time1
  3. It creates a Time1 object using the integer values read from the command line and assigns the reference to the variable t
  4. The method declares a reference variable times to designate an array of time objects
  5. Create an array for 5 time objects, store the reference of that array into the variable times
  6. Assign t to times[0]
  7. For positions 1 to 4 of the array designated by times, times[i] is times[i-1] plus t.
  8. Finally, print the result of calling the method isIncreasing using times

2 Time2

Let’s consider an alternative way of representing time values. Create a new class called Time2. Instead of having three instance variables (hours, minutes and seconds) like Time1, Time2 has a single instance variable, timeInSeconds. For instance, the time value 2:5:10 will be represented as

The maximum value for the variable timeInSeconds is the total number of seconds for a 24 hours period minus 1.

• Write a class called Time2 that implements all the methods that are implemented by the class Time1.

Note: Just like Time1, the constructor of the class Time2 has three parameters, hours, minutes, and seconds.

Copy the file Utils1.java to Utils2.java and make all the necessary changes so that Utils2 uses Time2 objects instead of Time1 objects.

3 Quiz (1 mark)

Knowing that the instance variable timeInSeconds of the class Time2 has been declared to be private. The following implementation of the method equals, within the class Time2, is valid. True or False.

Answer the question on Blackboard Learn:

• https://uottawa.blackboard.com/

Last Modified: January 29, 2015