WrClasses-WE4-P2

Section 10.11 WrClasses-WE4-P2

Subgoals for Writing a Class.

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

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Subsection 10.11.1

Exercises Exercises

1.

Q51: Identify all constructors.

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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." );
        }
    }

    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;
    }
}

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2.

Q52: Identify all accessor/getter methods.

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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." );
        }
    }

    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;
    }
}

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3.

Q53: Identify all mutator/setter methods.

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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." );
        }
    }

    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;
    }
}

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4.

Q54: Identify the attributes.

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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." );
        }
    }

    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;
    }
}

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5.

Q55: Identify the helper or auxiliary methods. Often any method that doesn’t fall into another category (constructor, accessor, mutator, toString, equals) is considered a helper or auxiliary method.

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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." );
        }
    }

    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;
    }
}

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