Assessment: Writing Classes 1

Section 9.8 Assessment: Writing Classes 1

Subgoals for Writing a Class.

Pick a name for the class, is usually a noun
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Differentiate class-level static vs. instance/object-level variables
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Differentiate class-level static vs. instance/object behaviors/methods
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Define instance variables (that you want to be interrelated)
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1. Name
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2. Data Type
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3. private
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Define class variables static as needed
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1. Name
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2. Data Type
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3. public / private / final
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Create constructor (behavior) that creates initial state of object
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1. Overloaded constructor (with as many parameters)
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2. public
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3. Same name as class
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4. No return type
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5. Default - no parameters
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6. Logic - initialize all variables
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7. Repeat as needed, adding parameters
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Create 1 accessor and 1 mutator behaviors per attribute
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1. Accessors
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  1. Name is get_<attr_name>
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  2. Public
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  3. Return type same data type as attribute
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  4. No parameters
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  5. Logic - return value
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2. Mutators
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  1. Name is set_<attr_name>
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  2. Public
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  3. Return type is void
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  4. Parameter is same data type as attribute
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  5. Logic validates input parameter and sets attribute value
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Write toString method
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1. public
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2. Returns String
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3. No parameters
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4. Logic - convert needed attributes to a format that can be printed
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Write equals method
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1. public
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2. Returns boolean
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3. Parameter - instance of the class
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4. Logic - compare attributes for equity
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Create additional methods as needed
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Exercises Exercises

1.

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." );
      }
   }

   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.

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public Coins( )
public Coins(int newQuarters, int newDimes, int newNickels, int newPennies)
public double total( )
public double convert( double rate )
public NewCoins()

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2.

Q2: Consider the following class definition.

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/* 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." );
      }
   }

   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.

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Coins
getQuarters, getDimes, getNickels, getPennies
setQuarters, setDimes, setNickels, setPennies
moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
total, convert

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3.

Q3: Consider the following class definition.

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/* 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." );
      }
   }

   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.

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Coins
getQuarters, getDimes, getNickels, getPennies
setQuarters, setDimes, setNickels, setPennies
moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
total, convert

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4.

Q4: Consider the following class definition.

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/* 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." );
      }
   }

   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?

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quarters, dimes, nickels, pennies
getQuarters, getDimes, getNickels, getPennies
setQuarters, setDimes, setNickels, setPennies
moneyFromQuarters, moneyFromDimes, moneyFromNickels, moneyFromPennies
total, convert

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