8.4. Assessment: Writing Classes 1¶
Subgoals for Writing a Class 3/4
Name it
Differentiate class-level (static) vs. instance/object-level variables
Differentiate class-level (static) vs. instance/object behaviors/methods
Define class variables (static) as needed ‘
Name
Data Type
public / private / final
Define instance variables (that you want to be interrelated)
Name
Data Type
private
Create constructor (behavior) that creates initial state of object
public
Same name as class
No return type
Default - no parameters
Logic - initialize all variables
Repeat as needed, adding parameters
Create 1 accessor and 1 mutator behaviors per attribute
Accessors
Name is get_<attr_name>
Public
Return type same data type as attribute
No parameters
Logic - return value
Mutators
Name is set_<attr_name>
Public
Return type is void
Parameter is same data type as attribute
Logic validates input parameter and sets attribute value
- public Coins( )
- public Coins(int newQuarters, int newDimes, int newNickels, int newPennies)
- public double total( )
- public double convert( double rate )
- public NewCoins()
- Coins
- getQuarters, getDimes, getNickels, getPennies
- setQuarters, setDimes, setNickels, setPennies
- moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
- total, convert
- Coins
- getQuarters, getDimes, getNickels, getPennies
- setQuarters, setDimes, setNickels, setPennies
- moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
- total, convert
- quarters, dimes, nickels, pennies
- getQuarters, getDimes, getNickels, getPennies
- setQuarters, setDimes, setNickels, setPennies
- moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
- total, convert
- Coins
- getQuarters, getDimes, getNickels, getPennies
- setQuarters, setDimes, setNickels, setPennies
- moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
- total, convert
Q1: Consider the following class defintion.
/* Coins Class */
public class Coins {
private int quarters;
private int dimes;
private int nickels;
private int pennies;
public Coins(int newQuarters, int newDimes, int newNickels, int newPennies) {
setQuarters( newQuarters );
setDimes( newDimes );
setNickels( newNickels );
setPennies( newPennies );
}
public Coins( ) {
setQuarters( 0 );
setDimes( 0 );
setNickels( 0 );
setPennies( 0 );
}
public int getQuarters( ) {
return quarters;
}
public void setQuarters( int newQuarters ) {
if ( newQuarters >= 0 )
quarters = newQuarters;
else {
System.out.println( "The number of quarters cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getDimes( ) {
return dimes;
}
public void setDimes( int newDimes ) {
if ( newDimes >= 0 )
dimes = newDimes;
else {
System.out.println( "The number of dimes cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getNickels( ) {
return nickels;
}
public void setNickels( int newNickels ) {
if ( newNickels >= 0 )
nickels = newNickels;
else {
System.out.println( "The number of nickels cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getPennies( ) {
return pennies;
}
public void setPennies( int newPennies ) {
if ( newPennies >= 0 )
pennies = newPennies;
else {
System.out.println( "The number of pennies cannot be negative." );
System.out.println( "Value not changed." );
}
}
public String toString( ) {
return( "quarters: " + quarters + "; dimes: " + dimes
+ "; nickels: " + nickels + "; pennies:" + pennies );
}
public boolean equals( Coins c ) {
return ( quarters == c.quarters && dimes == c.dimes
&& nickels == c.nickels && pennies == c.pennies );
}
private double moneyFromQuarters( ) {
return ( quarters * .25 );
}
private double moneyFromDimes( ) {
return ( dimes * .1 );
}
private double moneyFromNickels( ) {
return ( nickels * .05 );
}
private double moneyFromPennies( ) {
return ( pennies * .01 );
}
public double total( ) {
return moneyFromQuarters + moneyFromDimes + moneyFromNickels + moneyFromPennies;
}
public double convert( double rate ) {
return total * rate;
}
}
Identify all the constructors from the given class definition above. Choose all that apply.
Q2: Consider the following class definition.
/* Coins Class */
public class Coins {
private int quarters;
private int dimes;
private int nickels;
private int pennies;
public Coins(int newQuarters, int newDimes, int newNickels, int newPennies) {
setQuarters( newQuarters );
setDimes( newDimes );
setNickels( newNickels );
setPennies( newPennies );
}
public Coins( ) {
setQuarters( 0 );
setDimes( 0 );
setNickels( 0 );
setPennies( 0 );
}
public int getQuarters( ) {
return quarters;
}
public void setQuarters( int newQuarters ) {
if ( newQuarters >= 0 )
quarters = newQuarters;
else {
System.out.println( "The number of quarters cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getDimes( ) {
return dimes;
}
public void setDimes( int newDimes ) {
if ( newDimes >= 0 )
dimes = newDimes;
else {
System.out.println( "The number of dimes cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getNickels( ) {
return nickels;
}
public void setNickels( int newNickels ) {
if ( newNickels >= 0 )
nickels = newNickels;
else {
System.out.println( "The number of nickels cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getPennies( ) {
return pennies;
}
public void setPennies( int newPennies ) {
if ( newPennies >= 0 )
pennies = newPennies;
else {
System.out.println( "The number of pennies cannot be negative." );
System.out.println( "Value not changed." );
}
}
public String toString( ) {
return( "quarters: " + quarters + "; dimes: " + dimes
+ "; nickels: " + nickels + "; pennies:" + pennies );
}
public boolean equals( Coins c ) {
return ( quarters == c.quarters && dimes == c.dimes
&& nickels == c.nickels && pennies == c.pennies );
}
private double moneyFromQuarters( ) {
return ( quarters * .25 );
}
private double moneyFromDimes( ) {
return ( dimes * .1 );
}
private double moneyFromNickels( ) {
return ( nickels * .05 );
}
private double moneyFromPennies( ) {
return ( pennies * .01 );
}
public double total( ) {
return moneyFromQuarters + moneyFromDimes + moneyFromNickels + moneyFromPennies;
}
public double convert( double rate ) {
return total * rate;
}
}
Identify the accessor/getter methods.
Q3: Consider the following class definition.
/* Coins Class */
public class Coins {
private int quarters;
private int dimes;
private int nickels;
private int pennies;
public Coins(int newQuarters, int newDimes, int newNickels, int newPennies) {
setQuarters( newQuarters );
setDimes( newDimes );
setNickels( newNickels );
setPennies( newPennies );
}
public Coins( ) {
setQuarters( 0 );
setDimes( 0 );
setNickels( 0 );
setPennies( 0 );
}
public int getQuarters( ) {
return quarters;
}
public void setQuarters( int newQuarters ) {
if ( newQuarters >= 0 )
quarters = newQuarters;
else {
System.out.println( "The number of quarters cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getDimes( ) {
return dimes;
}
public void setDimes( int newDimes ) {
if ( newDimes >= 0 )
dimes = newDimes;
else {
System.out.println( "The number of dimes cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getNickels( ) {
return nickels;
}
public void setNickels( int newNickels ) {
if ( newNickels >= 0 )
nickels = newNickels;
else {
System.out.println( "The number of nickels cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getPennies( ) {
return pennies;
}
public void setPennies( int newPennies ) {
if ( newPennies >= 0 )
pennies = newPennies;
else {
System.out.println( "The number of pennies cannot be negative." );
System.out.println( "Value not changed." );
}
}
public String toString( ) {
return( "quarters: " + quarters + "; dimes: " + dimes
+ "; nickels: " + nickels + "; pennies:" + pennies );
}
public boolean equals( Coins c ) {
return ( quarters == c.quarters && dimes == c.dimes
&& nickels == c.nickels && pennies == c.pennies );
}
private double moneyFromQuarters( ) {
return ( quarters * .25 );
}
private double moneyFromDimes( ) {
return ( dimes * .1 );
}
private double moneyFromNickels( ) {
return ( nickels * .05 );
}
private double moneyFromPennies( ) {
return ( pennies * .01 );
}
public double total( ) {
return moneyFromQuarters + moneyFromDimes + moneyFromNickels + moneyFromPennies;
}
public double convert( double rate ) {
return total * rate;
}
}
Identify the mutator/setter methods.
Q4: Consider the following class definition.
/* Coins Class */
public class Coins {
private int quarters;
private int dimes;
private int nickels;
private int pennies;
public Coins(int newQuarters, int newDimes, int newNickels, int newPennies) {
setQuarters( newQuarters );
setDimes( newDimes );
setNickels( newNickels );
setPennies( newPennies );
}
public Coins( ) {
setQuarters( 0 );
setDimes( 0 );
setNickels( 0 );
setPennies( 0 );
}
public int getQuarters( ) {
return quarters;
}
public void setQuarters( int newQuarters ) {
if ( newQuarters >= 0 )
quarters = newQuarters;
else {
System.out.println( "The number of quarters cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getDimes( ) {
return dimes;
}
public void setDimes( int newDimes ) {
if ( newDimes >= 0 )
dimes = newDimes;
else {
System.out.println( "The number of dimes cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getNickels( ) {
return nickels;
}
public void setNickels( int newNickels ) {
if ( newNickels >= 0 )
nickels = newNickels;
else {
System.out.println( "The number of nickels cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getPennies( ) {
return pennies;
}
public void setPennies( int newPennies ) {
if ( newPennies >= 0 )
pennies = newPennies;
else {
System.out.println( "The number of pennies cannot be negative." );
System.out.println( "Value not changed." );
}
}
public String toString( ) {
return( "quarters: " + quarters + "; dimes: " + dimes
+ "; nickels: " + nickels + "; pennies:" + pennies );
}
public boolean equals( Coins c ) {
return ( quarters == c.quarters && dimes == c.dimes
&& nickels == c.nickels && pennies == c.pennies );
}
private double moneyFromQuarters( ) {
return ( quarters * .25 );
}
private double moneyFromDimes( ) {
return ( dimes * .1 );
}
private double moneyFromNickels( ) {
return ( nickels * .05 );
}
private double moneyFromPennies( ) {
return ( pennies * .01 );
}
public double total( ) {
return moneyFromQuarters + moneyFromDimes + moneyFromNickels + moneyFromPennies;
}
public double convert( double rate ) {
return total * rate;
}
}
Which of the choices lists attributes
of the given class?
Q5: Consider the following class definiton.
/* Coins Class */
public class Coins {
private int quarters;
private int dimes;
private int nickels;
private int pennies;
public Coins(int newQuarters, int newDimes, int newNickels, int newPennies) {
setQuarters( newQuarters );
setDimes( newDimes );
setNickels( newNickels );
setPennies( newPennies );
}
public Coins( ) {
setQuarters( 0 );
setDimes( 0 );
setNickels( 0 );
setPennies( 0 );
}
public int getQuarters( ) {
return quarters;
}
public void setQuarters( int newQuarters ) {
if ( newQuarters >= 0 )
quarters = newQuarters;
else {
System.out.println( "The number of quarters cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getDimes( ) {
return dimes;
}
public void setDimes( int newDimes ) {
if ( newDimes >= 0 )
dimes = newDimes;
else {
System.out.println( "The number of dimes cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getNickels( ) {
return nickels;
}
public void setNickels( int newNickels ) {
if ( newNickels >= 0 )
nickels = newNickels;
else {
System.out.println( "The number of nickels cannot be negative." );
System.out.println( "Value not changed." );
}
}
public int getPennies( ) {
return pennies;
}
public void setPennies( int newPennies ) {
if ( newPennies >= 0 )
pennies = newPennies;
else {
System.out.println( "The number of pennies cannot be negative." );
System.out.println( "Value not changed." );
}
}
public String toString( ) {
return( "quarters: " + quarters + "; dimes: " + dimes
+ "; nickels: " + nickels + "; pennies:" + pennies );
}
public boolean equals( Coins c ) {
return ( quarters == c.quarters && dimes == c.dimes
&& nickels == c.nickels && pennies == c.pennies );
}
private double moneyFromQuarters( ) {
return ( quarters * .25 );
}
private double moneyFromDimes( ) {
return ( dimes * .1 );
}
private double moneyFromNickels( ) {
return ( nickels * .05 );
}
private double moneyFromPennies( ) {
return ( pennies * .01 );
}
public double total( ) {
return moneyFromQuarters + moneyFromDimes + moneyFromNickels + moneyFromPennies;
}
public double convert( double rate ) {
return total * rate;
}
}
Identify the helper or auxiliary methods.