Question

Homework help in Java:
Java Au Naturel Chapter 6 exercise 6.5
I need help on how to revise the GrowthRates class to compound monthly.
Chapter is attached and class code in comments w exercise

Answer 1

Exercise 6.5 Revise GrowthRates to compound monthly. For instance, if the rate is 6% multiply by 1.005 each month, then tell the number of years and months to double.

Answer 2

@Kainui @ganeshie8 @Mimi_x3

Answer 3

these guys should know java

Answer 4

GrowthRates class

public class GrowthRates
{
/** Calculate time to double your money at a given rate. */

public GrowthRates()
{ String input = JOptionPane.showInputDialog ("Annual rate? 0 if done:");

double rate = Double.parseDouble (input);
while (rate > 0.0)
{ JOptionPane.showMessageDialog (null, "It takes " + yearsToDouble (rate) + " years for \nyour money to double.");
input = JOptionPane.showInputDialog ("Another rate (0 when done) :");
rate = Double.parseDouble (input);
}

}

/** Precondition: interestRate is positive. */
public int yearsToDouble (double interestRate)
{ double balance = 1.0;
int count = 0;
while (balance < 2.0)
{ balance = balance * (1.0 + interestRate / 100.0);
count++;
}

return count;
}
}

Answer 5

You can type ``` before and after a block of code to make it look a lot nicer:
```
public class GrowthRates
{
/** Calculate time to double your money at a given rate. */

public GrowthRates()
{ String input = JOptionPane.showInputDialog ("Annual rate? 0 if done:");

double rate = Double.parseDouble (input);
while (rate > 0.0)
{ JOptionPane.showMessageDialog (null, "It takes " + yearsToDouble (rate) + " years for \nyour money to double.");
input = JOptionPane.showInputDialog ("Another rate (0 when done) :");
rate = Double.parseDouble (input);
}

}

/** Precondition: interestRate is positive. */
public int yearsToDouble (double interestRate)
{ double balance = 1.0;
int count = 0;
while (balance < 2.0)
{ balance = balance * (1.0 + interestRate / 100.0);
count++;
}

return count;
}
}
```

So can you show me what you've tried?

Answer 6

so far, I did research and tried to understand what is means to compound monthly

Answer 7

it sounds like the exercise wants this, meaning that the interest is added to the total

Answer 8

Well honestly I don't know much or anything about financial stuff, I can really only help you on the Java side of this question.

Answer 9

So I decided to revise the appropriate method.

/** Precondition: interestRate is positive. */
/** Exercise 6.5
* Revising this method
*/
public int yearsToDouble (double interestRate)
{ double balance = 1.0;
int count = 0;
while (balance < 2.0)
{ balance = balance * (1.0 + interestRate / 100.0);
count++;
}

if (interestRate == 6) // if the rate is equal to 6 percent
{ balance = balance * (1.0 + interestRate * 1.005);
count++;
}
return count;
}

Answer 10

Hmm I don't think this will solve your problem, since it is more general than just altering the individual value of when the interest rate is 6. For instance, the relationship between 6% and 1.005 is that 1.005 is 100% + (6%)/12

So it's taking that 6% and dividing it by every month in the year and now as opposed to compounding the interest in a single year.

Answer 11

Okay,
How do you think I should type it, so that the program tells how many months for the money to double ?

For 6 % specifically it takes 13 years to double. I am confused on "tell the number of year and months to double. Does it mean how many months in 13 years or how many ears and months altogether it takes for the money to double?

Answer 12

So now, I altered the code more

public GrowthRatesV2()
{ String input = JOptionPane.showInputDialog ("Annual rate? 0 if done:");

double rate = Double.parseDouble (input);
double months1 = 30 * yearsToDouble (rate);
double months2 = 31 *yearsToDouble (rate);
double months = months1 = months2;
while (rate > 0.0)
{ JOptionPane.showMessageDialog (null, "It takes " + yearsToDouble (rate) + " years for \nyour money to double." + months + " months ");
input = JOptionPane.showInputDialog ("Another rate (0 when done) :");
rate = Double.parseDouble (input);

// double months1 = 30 * yearsToDouble (rate);
// double months2 = 31 *yearsToDouble (rate);
// double months = months1 || months2;

if (months1 >= 30)
if (months1 == 31)
JOptionPane.showMessageDialog (null, " It also takes " + months2 + " months for your money to double. ");

}

}

/** Precondition: interestRate is positive. */

/** Exercise 6.5
* Revising this method
*/
public int yearsToDouble (double interestRate)
{ double balance = 1.0;
int count = 0;

while (balance < 2.0)
{ balance = balance * (1.0 + interestRate / 100.0);
count++;
}

if (interestRate == 6) // if the rate is equal to 6 percent
{ balance = balance * (1.0 + interestRate * 1.005);
count++;
}
return count;
}