start is the first term, terms is the number of terms in the sequence, and step is the common difference. matchCount will be used in the equal method, and seq represents the comma separated string version of the sequence.

Constructor #$1-$ Takes a start value $($must be $1$ or greater$),$ number of terms $($must be $3$ or greater$),$ and a value for step $($must be $1$ or greater$).$ If an invalid value is passed in$,$ an IllegalArgumentException will be thrown with the message Invalid parameter and further initialization will not take place. If all the arguments are valid, it initializes the corresponding instance variables and assigns a value to seq $($see output for details$).$

Constructor #$2-$ Takes a start value $($must be $1$ or greater$)$ and a value for step $($must be $1$ or greater$).$ If an invalid value is passed in$,$ an IllegalArgumentException will be thrown with the message Invalid parameter and further initialization will not take place. If all the arguments are valid, it assumes the number of terms is five and assigns a value to seq $($see output for details$).$

Copy Constructor $-$ Define a copy constructor for the class.

getStep $-$ Get method for step.

setStep $-$ Set method for step. An IllegalArgumentException will be thrown with the message Invalid parameter and further initialization will not take place if an attempt is made to make step be an integer less than $1.$ Do not forget to update seq to match the new step value.

getMatchCount $-$ Get method for matchCount.

setMatchCount $-$ Set method for number of matchCount. An IllegalArgumentException will be thrown with the message Invalid parameter and further initialization will not take place if an attempt is made to make matchCount be an integer less than $1.$