渗透程序中的错误：线程“ main”中的异常java.lang.ArrayIndexOutOfBoundsException：0

Question

Hello I encountered this error while trying to run this program and I cannot figure out what's wrong with it:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at PercolationStats.main

and here is the code:

/****************************************************************
  * Compilation:  javac PercolationStats.java
  * Execution:    java PercolationStats N T
  * Dependencies: Percolation.java, StdStats.java, StdRandom.java,
  *               StdOut.java
  * 
  * % java PercolationStats 20 1000
  *      mean                    = 0.591100
  *      stddev                  = 0.046068
  *      95% confidence interval = 0.582071, 0.600129
  * 
  * % java PercolationStats 200 100
  *      mean                    = 0.593257
  *      stddev                  = 0.016242
  *      95% confidence interval = 0.592251, 0.594264
  * 
  ***************************************************************/

public class PercolationStats { 

    private int experimentsCount; 
    private Percolation pr; 
    private double[] fractions; 

    public PercolationStats(int N, int T) { 
        if (N <= 0 || T <= 0) { 
            throw new IllegalArgumentException("Given N <= 0 || T <= 0"); 
        } 

        experimentsCount = T; 
        fractions = new double[experimentsCount]; 
        for (int expNum = 0; expNum < experimentsCount; expNum++) { 
            pr = new Percolation(N); 
            int openedSites = 0; 
            while (!pr.percolates()) { 
              int i = StdRandom.uniform(1, N + 1); 
                int j = StdRandom.uniform(1, N + 1); 
                if (!pr.isOpen(i, j)) { 
                    pr.open(i, j); 
                    openedSites++; 
                } 
            } 
            double fraction = (double) openedSites / (N * N); 
            fractions[expNum] = fraction; 
        } 
    } 

    public double mean() { 
        return StdStats.mean(fractions); 
    } 

    public double stddev() { 
        return StdStats.stddev(fractions); 
    } 

    public double confidenceLo() { 
        return mean() - ((1.96 * stddev()) / Math.sqrt(experimentsCount)); 
    } 

    public double confidenceHi() { 
        return mean() + ((1.96 * stddev()) / Math.sqrt(experimentsCount)); 
    } 

    public static void main(String[] args) { 
        int N = Integer.parseInt(args[0]); 
        int T = Integer.parseInt(args[1]); 
        PercolationStats ps = new PercolationStats(N, T); 
        String confidence = ps.confidenceLo() + ", " + ps.confidenceHi(); 
        StdOut.println("mean                    = " + ps.mean()); 
        StdOut.println("stddev                  = " + ps.stddev()); 
        StdOut.println("95% confidence interval = " + confidence); 
    } 
}

Answer 1

This looks like some fairly carefully written code from another source.

Where it is almost certainly failing is that it is expecting you to provide some arguments to the program. You can see how to do this in the comments at the top of the code. Try running it with

java PercolationStats 20 1000

and see what happens.

If you're running this from inside eclipse, you can set the arguments in the run configuration.