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Trying to convert this formula into an arithmetic expression in Java

I'm trying to take user input in the form of myMonthlyPayment, myAnnualInterestRate, and myPrincipal in order to calculate the number of months needed to pay off debt by using The formula I've attached to this post. What I have in eclipse for the formula right now is:
monthsNeeded = ((Math.log(myMonthlyPayment) - Math.log(myMonthlyPayment)
- ((myAnnualInterestRate / 1200.0) * myPrincipal))
/ ((Math.log(myAnnualInterestRate) / 1200.0) + 1.0));
I should be getting an output of 79 months with the inputs I'm using but instead I'm getting -62. I know the formula is correct, I'm almost positive I've made a mistake somewhere in the translation of it into Java. If someone could point it out that would be greatly appreciated!

So I've fixed it, with a sample input and output.
I didn't put much effort into making this code beautiful but you can see that even separating it into 3 parts using method extraction (although I didn't know how to name them, lacking the domain knowledge) made the code easier to understand.
public class Example {
public static void main(String[] args) {
double myMonthlyPayment = 2000;
double myAnnualInterestRate = 5;
double myPrincipal = 200000;
System.out.println(a(myMonthlyPayment));
System.out.println(b(myPrincipal, myAnnualInterestRate, myMonthlyPayment));
System.out.println(c(myAnnualInterestRate));
double monthsNeeded = (a(myMonthlyPayment) - b(myPrincipal, myAnnualInterestRate, myMonthlyPayment))
/ c(myAnnualInterestRate);
System.out.println(monthsNeeded);
}
private static double c(double myAnnualInterestRate) {
return Math.log((myAnnualInterestRate / 1200.0) + 1);
}
private static double b(double myPrinicipal, double myAnnualInterestRate, double myMonthlyPayment) {
return Math.log(myMonthlyPayment - (myAnnualInterestRate / 1200.0) * myPrinicipal);
}
private static double a(double myMonthlyPayment) {
return Math.log(myMonthlyPayment);
}
}

I think this is what you're looking for:
monthsNeeded = (Math.log(myMonthlyPayment) - Math.log(myMonthlyPayment - myAnnualInterestRate / 1200d * myPrincipal)) / Math.log(myAnnualInterestRate / 1200d + 1);
It seems that, in your solution, you weren't calculating your myAnnualInterestRate/1200*myPrincipal inside your second Math.log(...). You had also left some calculations outside of Math.log(...) in the bottom half of your equation.
If you have an equation that does an operation inside a natural log, when you convert that equation to Java code, the operation needs to still be done, inside the natural log:
ln(someNumber + 10)
would be converted to:
Math.log(someNumber + 10),
NOT:
Math.log(someNumber) + 10
Hope this helps and good luck. :)

Setter can't modify the field properly

I am encountering a problem when creating a program to solve simple kinematics.
I run the program and find out the fields haven't been modified properly . Here is
the scrap of my program that initialise the object and setting the variables.
public class LinearConstantAcceleration1DKinematics {
private double distance;
private double speed;
private double acceleration;
private double time;
public LinearConstantAcceleration1DKinematics() {
/* initialize the object */
distance = 0;
speed = 0;
acceleration = 0;
time = 0;
}
public void setS(double s) {
this.distance = s;
}
//continue with 3 more setters which is created in the same way ,i have omitted them here
public double getU(){
double u_ans;
u_ans = (distance - 1/2 *acceleration*time*time )/time;
return u_ans;
}
}
And here is the main that uses the methods
LinearConstantAcceleration1DKinematics kinematics = new LinearConstantAcceleration1DKinematics();
kinematics.setS(175);
kinematics.setA(10);
kinematics.setT(5);
System.out.printf(%f\n", kinematics.getU());
The result is 35 which is incorrect.Many thanks for your help.

This has absolutely nothing to do with setter methods -- your division is wrong since 1 / 2 does int division and returns 0 resulting in the equation calculating simply distance / time.
Change to:
u_ans = (distance - 1.0 / 2.0 * acceleration * time * time) / time;
Lesson to learn: don't assume where the error is -- test it. Use a debugger or println statements to check the states of your variables as your program runs.

Trying to make a simple falling ball program

This is what I have so far. It tells me that I have a syntax error on the lines marked below, saying that it expected a "{" and a "}" respectively, without the double quotes around them. Any suggestions?
public class attempt1 {
//use Euler-Richardson algorithm
//defining the initial conditions
double v0=30;
double theta=40;
double x0=0;
double y0=0;
double v0x=v0*Math.cos(Math.toRadians(theta));
double v0y=v0*Math.sin(Math.toRadians(theta));
double dt= .01;
double ax=0;
double ay=-9.8;
double x=0;
double y=0; //this line here, on the semi-colon
while (y>=0) {
double vx= v0x+1/2*ax*dt;
double vy= v0y+1/2*ay*dt;
double x= x0+1/2*vx*dt;
double y= y0+1/2*vy*dt;
if (y<=0){System.out.println(x);}
}
} //and right over here, on the brace itself

You are trying to run statements inside a class body. They should be in a method. like this:
public class Attempt1{
private void doSomething(){
//example code
int a = 1 + 1;
while (a < 2) {
//do random stuff
}
}
}
Right now you have something similar to this:
public class Attempt1 {
//while{...} <---- WRONG!
}
Statements should be in a method (sometimes called function) at all times.
You can however put variables outside a method. This will make them accessible for all methods in that class.
You should check out some starting tutorials like the one Oracle gives:
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/

implementation formula volume of a sphere with Java and JUnit?

I have to make an implementation to calculate volume of a sphere to be checked with JUnit test, but there are some errors. The formula is correct, but when I test it, it doesn't work :
class VolumeSphere.java
public class VolumeSphere {
public static double volsph(double j) {
double volume;
double const = 1.33;
double phi = 3.14;
volume = const * phi * (j * j * j);
return volume;
}
}
and then this the test file :
VolumeSphereTest.java
import junit.framework.*;
public class VolumeSphereTest extends TestCase {
public VolumeSphereTest(String name) {
super(name);
}
public void testSimple() {
assertEquals(33.4096, VolumeSphere.volsph(2.0));
}
}
when I run the JUnit test, it's said "Expected: (33.4096) but was: (33.4096000005)."
So, what should I do? Thankyou in advance for the help!

The problem is that 33.4096 isn't exactly represented by a double, nor is 1.33, and nor is 3.14. Moreover, the multiplication introduces its own errors. Therefore, the assertEquals needs to be replaced by something that basically means "assert that the value is very close to what we expect".
JUnit has assertEquals(expectedValue, actualValue, errorPermitted) for comparing doubles, which is what you should use here.
In general, double is a poor choice of data type for doing exact arithmetic with numbers expressed as decimals, because it stores binary representations of numbers. If you want accuracy with exact decimals, use BigDecimal instead.

const is a keyword and can't be a name of a variable - pick a different name for your variable.

The problem is that the answer isn't exactly the value you let the JUnit test compare to. The answer is 33.409600000000005 instead of 33.4096. To remedy this, you could use assertEquals(33.4096, VolumeSphere.volsph(2.0), 0.0001);.
This will allow all answers within a difference of 0.0001 around 33.4096. Therefor in this case it will allow 33.4095 to 33.4097.
Also, instead of using double phi = 3.14, you could use Math.PI, which inserts the more significant value of constant pi.

call method that rounds java

OK so I can't understand why it says the method isn't being used locally.... The private String formatNumber() method is saying this.
Basically what I need to do is have a method that returns the circumference
- another method that rounds numbers to 2 decimal places and returns a string
- and another method that returns the formatted version of circumference...
It's not hard to see what I'm trying to do, but it gives me the above stated error and I can't figure it out.
//figures out circumference
public double getCircumference(){
circumference = 2 * Math.PI * radius;
return circumference;
}
//takes string and turns back into a double
public double getFormattedCircumference(){
double x = Double.parseDouble(format);
return x;
}
//this method is giving the error of not being used locally...
//method takes double and turns to string so that it can be formatted and it
has to be a string
private String formatNumber(double x){
x = circumference;
NumberFormat number = NumberFormat.getNumberInstance();
number.setMaximumFractionDigits(2);
String format = number.format(x);
return format;
}

You've declared the private method but you've not used it in your current code anywhere and so the compiler is warning you of this (check your program to see if you're calling this method anywhere).
Incidentally, what you're seeing is a warning not an error. Your code should still compile, and the program will still run (if there are no errors present).
Edit 1
You've a serious problem with the method, and maybe more than one, in that it takes in a double parameter and then promptly discards it. Why? If you want to format the number that is passed in as a parameter, then you don't want to discard that parameter. Also, do you want to make this method public so that it can be called by objects outside of this class? Also, will the method have state or will it be stateless? Will it use the fields of the class, or will it only format the number passed into it. If the latter, than it should be a static method.

I got it all figured out. I was making it harder than it actually was.
//figures out circumference
public double getCircumference(){
circumference = 2 * Math.PI * radius;
return circumference;
}
public String getFormattedCircumference(){
return formatNumber(getCircumference());
}
//formats to two decimal places.
private String formatNumber(double x){
NumberFormat number = NumberFormat.getNumberInstance();
number.setMaximumFractionDigits(2);
String format = number.format(x);
return format;
}