Java Error 'error: cannot find symbol'

Question

I am in the process of learning Java. Below is the program that I've been trying to compile, but cannot figure out why 'x' in line 38 provides the following error: 'cannot find symbol'. Any help would be greatly appreciated.

import java.util.Scanner;
class metropolis_HW2_7 {
 static int count = 0;
 public static void main(String[] args) {
 double a = 0.;
 double b = Math.PI;
 Scanner sc = new Scanner(System.in);
 while (true) {
 System.out.println(" Number of bins?");
 int nbin = sc.nextInt();
 if (nbin < 1)
 System.exit(0);
 double[] bin = new double[nbin];
 System.out.println(" Number of histories to run?");
 int N = sc.nextInt();
 double dx = (b - a) / nbin;
 for (int i = 0; i < N; i++) {
 if (count == 0) {
 double squiggle1 = Math.PI * Math.random();
 double squiggle2 = Math.PI * Math.random();
 double y_1 = 2 * squiggle1 + Math.sin(squiggle1);
 double y_2 = 2 * squiggle2 + Math.sin(squiggle2);
 if (y_2 < y_1) {
 squiggle1 = squiggle2;
 double x = squiggle2;
 } else {
 squiggle1 = squiggle1;
 double x = squiggle2 / squiggle1;
 }
 count++;
 } else {
 double squiggle1;
 double x = Sample(squiggle1);
 }
 int binNumber = (int) ((x - a) / dx);
 bin[binNumber] += 1.;
 }
 double x = a - dx / 2.;
 for (int i = 0; i < nbin; i++) {
 x += dx;
 bin[i] /= N * dx;
 System.out.printf(" Bin %15ドルd Sample for x = %27ドル.5f is %37ドル.5f vs %47ドル.5f Ratio (%5$f) \n", i, x, bin[i], PDF(x), bin[i] / PDF(x));
 }
 }
 }
 static double Sample(double squiggle1) {
 double squiggle2 = Math.PI * Math.random();
 double y_1 = 2 * squiggle1 + Math.sin(squiggle1);
 double y_2 = 2 * squiggle2 + Math.sin(squiggle2);
 if (y_2 < y_1) {
 squiggle1 = squiggle2;
 return squiggle2;
 } else {
 squiggle1 = squiggle1;
 return squiggle2 / squiggle1;
 }
 count++;
 }
 static double PDF(double x) {
 return (2 * x + Math.sin(x)) / (Math.pow(Math.PI, 2) + 2);
 }
}

• maneesh: Crossposted at coderanch.com/t/645832/java/java/…

Answer 1

Variables only exist inside the scope (between { and }) they're declared in. You have three different variables called x, and none of them exist when the line int binNumber=(int)((x-a)/dx); is executed.

Declare a variable outside the if statements, and then assign it inside it, something like this: (I've removed most of your code to make this example clearer; obvious you still need it)

double x;
if (count==0) {
 if (y_2<y_1) {
 x=squiggle2;
 } else {
 x=squiggle2/squiggle1;
 }
} else {
 x=Sample(squiggle1);
}
int binNumber=(int)((x-a)/dx);

Answer 2

Declare double x variable globally.You are declared in else part thats why it could not find the variable.

Scope variable Example:

 int a = 80; // Create a global variable "a"
void setup() {
 size(640, 360);
 background(0);
 stroke(255);
 noLoop();
}
void draw() {
 // Draw a line using the global variable "a"
 line(a, 0, a, height);
 // Create a new variable "a" local to the for() statement 
 for (int a = 120; a < 200; a += 2) {
 line(a, 0, a, height);
 }
 // Create a new variable "a" local to the draw() function
 int a = 300;
 // Draw a line using the new local variable "a"
 line(a, 0, a, height); 
 // Make a call to the custom function drawAnotherLine()
 drawAnotherLine();
 // Make a call to the custom function setYetAnotherLine()
 drawYetAnotherLine();
}
void drawAnotherLine() {
 // Create a new variable "a" local to this method
 int a = 320;
 // Draw a line using the local variable "a"
 line(a, 0, a, height);
}
void drawYetAnotherLine() {
 // Because no new local variable "a" is set, 
 // this line draws using the original global
 // variable "a", which is set to the value 80.
 line(a+2, 0, a+2, height);
}

Answer 3

The variable x is not declared in the scope in which it is used at that line. You are defining and assigning the double x inside two different if-blocks. Try declaring the variable in a broader scope (say, before the if-block, then assign it locally. Then it will be accessible in all 3 places.

Here's a simple example to explain what I mean:

void method()
{
 if (2 > 1)
 double x = 2;
 else
 double x = 3;
 System.out.println(x); //ERROR, because x is out of scope
}

So change it to

void method()
{
 double x = 0;
 if (2 > 1)
 x = 2;
 else
 x = 3;
 System.out.println(x); //No error; x is referenced in the same scope in which it is declared
}